2011 Vol. 33 No. zk1
Abstract：
Landslides are usually reinforced by anti-slide piles, and a very important problem is to determine the reasonable position of the anti-slide piles in the slope. It is considered that the optional position of the anti-slide piles is the position which can make the largest safety factor of the landslides. Based on the deformation field obtained by variable modulus of strength reduction method, this study finds that when the anti-slide piles setting in the position which has the largest displacement of the landslides can get the maximum safety factor, therefore, a reasonable location of the reinforcement by means of the anti-slide piles can be determined through the deformation field. The proposed method is convenient and reasonable. The results obtained can be a reference value to determine the location of the anti-slide piles.
Landslides are usually reinforced by anti-slide piles, and a very important problem is to determine the reasonable position of the anti-slide piles in the slope. It is considered that the optional position of the anti-slide piles is the position which can make the largest safety factor of the landslides. Based on the deformation field obtained by variable modulus of strength reduction method, this study finds that when the anti-slide piles setting in the position which has the largest displacement of the landslides can get the maximum safety factor, therefore, a reasonable location of the reinforcement by means of the anti-slide piles can be determined through the deformation field. The proposed method is convenient and reasonable. The results obtained can be a reference value to determine the location of the anti-slide piles.
Abstract：
Loess is a typical structural soil, and its seismic subsidence is mainly due to the internal microstructure and external load. Seismic subsidence of loess is a congregated macroscopical phenomenon of microstructure with the external load in different time and space. The distribution of loess particles and pores is obtained through electron microscope scanning experiments. The structural damage model is established by means of the statistical microscopic damage mechanics and structural mechanics. It explains the inherent damage mechanism of seismic subsidence, and the complete constitutive relation is obtained. The results indicate that the seismic subsidence of loess results from the damage of particular trellis pores and particles falling into trellis pores. It appears that there's a great relation between the seismic subsidence of loess and the dynamic stress and the distribution of particles and pores.
Loess is a typical structural soil, and its seismic subsidence is mainly due to the internal microstructure and external load. Seismic subsidence of loess is a congregated macroscopical phenomenon of microstructure with the external load in different time and space. The distribution of loess particles and pores is obtained through electron microscope scanning experiments. The structural damage model is established by means of the statistical microscopic damage mechanics and structural mechanics. It explains the inherent damage mechanism of seismic subsidence, and the complete constitutive relation is obtained. The results indicate that the seismic subsidence of loess results from the damage of particular trellis pores and particles falling into trellis pores. It appears that there's a great relation between the seismic subsidence of loess and the dynamic stress and the distribution of particles and pores.
Abstract：
In the conventional methods for calculating the ultimate bearing capacity of subsoil, the surcharge soil is taken as a surcharging load, and the strength of the soil burying the foundation is not considered. In order to consider the ratio of the bearing capacity provided by the soil strength of the surcharge soil, the bearing capacity of subsoil is calculated by means of both the finite element method (FEM) and the conventional method. The bearing capacity provided by the surcharge soil is then estimated by comparing the results calculated by the FEM and those by the conventional method.
In the conventional methods for calculating the ultimate bearing capacity of subsoil, the surcharge soil is taken as a surcharging load, and the strength of the soil burying the foundation is not considered. In order to consider the ratio of the bearing capacity provided by the soil strength of the surcharge soil, the bearing capacity of subsoil is calculated by means of both the finite element method (FEM) and the conventional method. The bearing capacity provided by the surcharge soil is then estimated by comparing the results calculated by the FEM and those by the conventional method.
Abstract：
Desulphogypsum soil cemedine is a new type of soil cementing agent. Based on a large number of lab tests on the stabilized soil cemented with ordinary portland cement and desulphogypsum soil cemedine respectively, the data on unconfined compressive strength, shearing strength, compressive modulus and permeability coefficient of these two kinds of stabilized soil are provided. By contrasting and analyzing the data, it shows that the stabilized soil cemented with desulphogypsum soil cemedine is much better than that stabilized with ordinary portland cement in compressive strength and shear strength, and the property of compressibility and permeability can satisfy the engineering demand. Meanwhile, the relationships among strength, curing age, mixing ratio and water content are verified, and the mechanism is also analyzed. It is demanstrated that the desulphogypsum soil cemedine used to deep mixing piles is suitable for engineering especially in soft soil regions with high moisture content.
Desulphogypsum soil cemedine is a new type of soil cementing agent. Based on a large number of lab tests on the stabilized soil cemented with ordinary portland cement and desulphogypsum soil cemedine respectively, the data on unconfined compressive strength, shearing strength, compressive modulus and permeability coefficient of these two kinds of stabilized soil are provided. By contrasting and analyzing the data, it shows that the stabilized soil cemented with desulphogypsum soil cemedine is much better than that stabilized with ordinary portland cement in compressive strength and shear strength, and the property of compressibility and permeability can satisfy the engineering demand. Meanwhile, the relationships among strength, curing age, mixing ratio and water content are verified, and the mechanism is also analyzed. It is demanstrated that the desulphogypsum soil cemedine used to deep mixing piles is suitable for engineering especially in soft soil regions with high moisture content.
Abstract：
Taocha-Shahe main canal, which is a fully excavated canal of Phase I of Middle Route Project of South-to-North Water Diversion, has a high slope and high-level groundwater. The effect of drainage system in the slope is vital to the safety of the slope and concrete linings. The seepage fields under different conditions are simulated by means of the finite element method associated with drainage designs of the slope. It follows from comparison of the simulated results that the influences on the seepage fields may be neglected while the distance from the boundary of groundwater to the slope is over 600 meters and the altitude of bottom boundary is lower than 75 meters. The sand filter layer under the concrete linings plays an important role in the drainage effects, or there should be 5 layers of drainage pipes to maintain the drainage effects if no sand filter layer exists. The research results provide important references for the design of the slope drainage system.
Taocha-Shahe main canal, which is a fully excavated canal of Phase I of Middle Route Project of South-to-North Water Diversion, has a high slope and high-level groundwater. The effect of drainage system in the slope is vital to the safety of the slope and concrete linings. The seepage fields under different conditions are simulated by means of the finite element method associated with drainage designs of the slope. It follows from comparison of the simulated results that the influences on the seepage fields may be neglected while the distance from the boundary of groundwater to the slope is over 600 meters and the altitude of bottom boundary is lower than 75 meters. The sand filter layer under the concrete linings plays an important role in the drainage effects, or there should be 5 layers of drainage pipes to maintain the drainage effects if no sand filter layer exists. The research results provide important references for the design of the slope drainage system.
Abstract：
In the construction of modern high rockfill dams, the key technologies concerning the design and construction of high rockfill dams mainly include: selection and application of dam construction materials, foundation treatment measures and the interaction of seepage control structures and dam, dam deformation control and prevention of local structure damages. For high earth core rockfill dams, the main consideration of materials is the application of gravel soil. For concrete faced rockfill dams, the key issue is rockfill deformation control and coordination. For construction of rockfill dams in future, the dam construction scale will be very huge and the construction conditions will be more and more complicated. Great challenges will be faced in geotechnical engineering. Among these, the engineering properties of rockfill (mainly particles breakage and long-term deformation), constitutive models of rockfill and gravel soils, back analysis of the parameters of dam construction materials, hydraulic fracture of earth core are the main geotechnical problems for construction of high rockfill dams.
In the construction of modern high rockfill dams, the key technologies concerning the design and construction of high rockfill dams mainly include: selection and application of dam construction materials, foundation treatment measures and the interaction of seepage control structures and dam, dam deformation control and prevention of local structure damages. For high earth core rockfill dams, the main consideration of materials is the application of gravel soil. For concrete faced rockfill dams, the key issue is rockfill deformation control and coordination. For construction of rockfill dams in future, the dam construction scale will be very huge and the construction conditions will be more and more complicated. Great challenges will be faced in geotechnical engineering. Among these, the engineering properties of rockfill (mainly particles breakage and long-term deformation), constitutive models of rockfill and gravel soils, back analysis of the parameters of dam construction materials, hydraulic fracture of earth core are the main geotechnical problems for construction of high rockfill dams.
Abstract：
The mechanical equilibrium problem in shield tunneling is analytically analyzed. The equilibrium equation between thrust force of shield machine and tunneling resistance is proposed. Taking account of the coupled reaction between shield machine and soils, a new mechanism model for controlling the earth pressure acting on the headchamber is presented. The optimal procure is developed for controlling the earth pressure acting on the headchamber. The numerical simulation shows that the controlling time will take about 20 s while the rotation speed of screw conveyor is singly adjusted, and the controlling time will take about 10 s while the rotation speed of screw conveyor and thrust force are simultaneously adjusted. The effectiveness and preciseness of the proposed model are verified by numerical results.
The mechanical equilibrium problem in shield tunneling is analytically analyzed. The equilibrium equation between thrust force of shield machine and tunneling resistance is proposed. Taking account of the coupled reaction between shield machine and soils, a new mechanism model for controlling the earth pressure acting on the headchamber is presented. The optimal procure is developed for controlling the earth pressure acting on the headchamber. The numerical simulation shows that the controlling time will take about 20 s while the rotation speed of screw conveyor is singly adjusted, and the controlling time will take about 10 s while the rotation speed of screw conveyor and thrust force are simultaneously adjusted. The effectiveness and preciseness of the proposed model are verified by numerical results.
Abstract：
An improved Hvorslev envelope-based three-dimensional elastoplastic constitutive model was proposed by Yao et al. (2008) for overconsolidated clays. The return mapping algorithm is adopted in order to implement the constitutive model into a finite element analysis software ABAQUS through the user material subroutine interface. By coupling the model with the Biot’s consolidation theory, coupled analyses of the localized deformation on overconsolidated clay specimens under undrained boundary conditions in triaxial compression and extension and plane strain stress states are performed. The numerical results show that the same stress paths are seen for the elements inside and outside the shear band. The elements in the vicinities of the shear band behave volume contracted, while the elements inside the shear band keep shear dilatancy during shear. The shear dilatancy is accompanied by the development of the shear band, and negative pore pressure appears inside the shear band and their vicinities. The changes in the pore water pressure and volumetric strain in the plane strain are between triaxial compression and extension stresses, but shear bands early occur in the plane strain.
An improved Hvorslev envelope-based three-dimensional elastoplastic constitutive model was proposed by Yao et al. (2008) for overconsolidated clays. The return mapping algorithm is adopted in order to implement the constitutive model into a finite element analysis software ABAQUS through the user material subroutine interface. By coupling the model with the Biot’s consolidation theory, coupled analyses of the localized deformation on overconsolidated clay specimens under undrained boundary conditions in triaxial compression and extension and plane strain stress states are performed. The numerical results show that the same stress paths are seen for the elements inside and outside the shear band. The elements in the vicinities of the shear band behave volume contracted, while the elements inside the shear band keep shear dilatancy during shear. The shear dilatancy is accompanied by the development of the shear band, and negative pore pressure appears inside the shear band and their vicinities. The changes in the pore water pressure and volumetric strain in the plane strain are between triaxial compression and extension stresses, but shear bands early occur in the plane strain.
Abstract：
The capillary water can reduce the strength of the silty subgrade and affect the durability and usability of the pavement. The key of treating silty subgrade is to reduce and control the action of the capillary water. Three methods, solidification method, geotextile speration method and butter layer method, are applied for treating the silty subgrade by means of the capillary model test and the field test. The model test results reveal that the effect of the lime-soil cured for 45 days adding composite geomembrane is similar to that of the gravel cushion and coarse sand cushion. The field test results indicate that the effect of the gravel cushion and the coarse sand cushion isolating capillary water is better than that of the composite geomembrane and the 3% cement-soil cushion; and that of the 5% lime-soil is the worst. Based on the two test results and practical engineering, the method of lime-soil adding composite geomembrane is recommended to treat the capillary water in silty subgrade.These two tests results can be the basis of the engineering design.
The capillary water can reduce the strength of the silty subgrade and affect the durability and usability of the pavement. The key of treating silty subgrade is to reduce and control the action of the capillary water. Three methods, solidification method, geotextile speration method and butter layer method, are applied for treating the silty subgrade by means of the capillary model test and the field test. The model test results reveal that the effect of the lime-soil cured for 45 days adding composite geomembrane is similar to that of the gravel cushion and coarse sand cushion. The field test results indicate that the effect of the gravel cushion and the coarse sand cushion isolating capillary water is better than that of the composite geomembrane and the 3% cement-soil cushion; and that of the 5% lime-soil is the worst. Based on the two test results and practical engineering, the method of lime-soil adding composite geomembrane is recommended to treat the capillary water in silty subgrade.These two tests results can be the basis of the engineering design.
Abstract：
The tailings dam is a special rock and soil engineering, and it is also a man-made mine industrial structure with high potential energy debris flow. The stability of the tailings dam decides the security of tailings pond. The researches on stability of the tailings dam is the forefront topic in geotechnical engineering field that is difficult to work out. Its structural features, geometric shapes, service mode, environmental media and mechanical behavior are considered. Its special nature and complexity of the tailings dam are summarized. The technical approaches for the safety management of the tailings dam are proposed, which is the on-line automatic monitoring and early warning information. It can provide a strong theoretical basis for the security monitoring and management of the tailings dam. The on-line automatic monitoring system for the tailings dam has full implementation of the information. It is applied in Lingnan Gold Mine, Xiadian Gold Mine and Hedong Gold Mine in Zhaoyuan, Shandong Province, and achieves good effectiveness.
The tailings dam is a special rock and soil engineering, and it is also a man-made mine industrial structure with high potential energy debris flow. The stability of the tailings dam decides the security of tailings pond. The researches on stability of the tailings dam is the forefront topic in geotechnical engineering field that is difficult to work out. Its structural features, geometric shapes, service mode, environmental media and mechanical behavior are considered. Its special nature and complexity of the tailings dam are summarized. The technical approaches for the safety management of the tailings dam are proposed, which is the on-line automatic monitoring and early warning information. It can provide a strong theoretical basis for the security monitoring and management of the tailings dam. The on-line automatic monitoring system for the tailings dam has full implementation of the information. It is applied in Lingnan Gold Mine, Xiadian Gold Mine and Hedong Gold Mine in Zhaoyuan, Shandong Province, and achieves good effectiveness.
Abstract：
Seismic slope dynamic response and the deformation mechanism are the premises of analyzing the dynamic stability of slopes. The response regulation of a bedding rock slope under the seismic action is discussed by using the three-dimensional finite difference software FLAC3D. The deformation mechanism is analyzed through the plastic zone, displacement time-histories as well as changes of shear strain increment of key elements. The calculation shows that, under the seismic action, the amplification coefficients of the horizontal and vertical peak accelerations of the bedding rock slopes increase with the increasing elevation and come to the maximum at the structural plane and the top of the slope; those at the top of the slope increase with the decrease of the distance from the slope surface and come to the maximum at the structural plane; the rock mass has vertical amplification effect on the input seismic waves and its filtering effect is inferior to the soil slope; the deformation damage of rock slopes mainly comes from the weak structural plane, formed by upper tension failure and bottom shear failure; the research also gives the methods of determining the position of the sliding surface of bedding rock slope’s and the judgment of slope instability. The results of the research have certain significance to analyzing the stability of bedding rock slopes and seismic design.
Seismic slope dynamic response and the deformation mechanism are the premises of analyzing the dynamic stability of slopes. The response regulation of a bedding rock slope under the seismic action is discussed by using the three-dimensional finite difference software FLAC3D. The deformation mechanism is analyzed through the plastic zone, displacement time-histories as well as changes of shear strain increment of key elements. The calculation shows that, under the seismic action, the amplification coefficients of the horizontal and vertical peak accelerations of the bedding rock slopes increase with the increasing elevation and come to the maximum at the structural plane and the top of the slope; those at the top of the slope increase with the decrease of the distance from the slope surface and come to the maximum at the structural plane; the rock mass has vertical amplification effect on the input seismic waves and its filtering effect is inferior to the soil slope; the deformation damage of rock slopes mainly comes from the weak structural plane, formed by upper tension failure and bottom shear failure; the research also gives the methods of determining the position of the sliding surface of bedding rock slope’s and the judgment of slope instability. The results of the research have certain significance to analyzing the stability of bedding rock slopes and seismic design.
Abstract：
Considering the characteristics of frost heaving and thawing of permafrost ， combining with the only supporting structure of L-type retaining wall used in the section from Golmud to Lhasa , Qinghai-Tibet Railway , the ground temperature, earth pressure and frost heaving forces and level deformation are tested. Due to the excavation and construction disturbance, the ground heat balance of the natural state is damaged. All the test indices are affected by cyclic ground temperature. But as an open project engineering structure, as long as there are no new disturbances, this balance is to gradually form a stable state, or to recover. In addition, the earth pressure and frozen-heave force should be revised by the actual deformation.
Considering the characteristics of frost heaving and thawing of permafrost ， combining with the only supporting structure of L-type retaining wall used in the section from Golmud to Lhasa , Qinghai-Tibet Railway , the ground temperature, earth pressure and frost heaving forces and level deformation are tested. Due to the excavation and construction disturbance, the ground heat balance of the natural state is damaged. All the test indices are affected by cyclic ground temperature. But as an open project engineering structure, as long as there are no new disturbances, this balance is to gradually form a stable state, or to recover. In addition, the earth pressure and frozen-heave force should be revised by the actual deformation.
Abstract：
The stress, deformation and seepage status of Shuibuya high concrete face rockfill dam (CFRD) are estimated according to its monitoring data since completed three years ago. The radial basis function neural network (RBF-ANN) is adopted to get constitutive model parameters based on the measured displacement data. The inversion results of Shuibuya CRFD show that the calculated settlements fit well with the measured ones, and the dam deformation is within a reasonable range and tends to be stable.
The stress, deformation and seepage status of Shuibuya high concrete face rockfill dam (CFRD) are estimated according to its monitoring data since completed three years ago. The radial basis function neural network (RBF-ANN) is adopted to get constitutive model parameters based on the measured displacement data. The inversion results of Shuibuya CRFD show that the calculated settlements fit well with the measured ones, and the dam deformation is within a reasonable range and tends to be stable.
Abstract：
The regional groundwater level is affected by several factors and highly nonlinear. Aiming at unstable change and highly nonlinear characteristics of the regional groundwater level, the grey Markov chain model is presented by means of combining the grey system theory with the dispersed Markov chain theory. The mean and standard deviations of information series are taken as the classification standard of precipitation states. The variance of the regional groundwater level for the past 14 years in the irrigating areas is classified into five classes according to the precipitation data. The predication results show that the model is feasible.
The regional groundwater level is affected by several factors and highly nonlinear. Aiming at unstable change and highly nonlinear characteristics of the regional groundwater level, the grey Markov chain model is presented by means of combining the grey system theory with the dispersed Markov chain theory. The mean and standard deviations of information series are taken as the classification standard of precipitation states. The variance of the regional groundwater level for the past 14 years in the irrigating areas is classified into five classes according to the precipitation data. The predication results show that the model is feasible.
Abstract：
Expansive soil (rock) has special engineering features. The canal slope of expansive soil is instable. It is difficult to deal with the canal slopes of expansive soil. The level of monitoring technology is higher. The selection, layout and laying technology of monitoring equipments as well as the monitoring methods of horizontal displacement, water content, suction, pore water pressure, earth pressure in the canal slopes of expansive soil (rock) are summarized. The stability monitoring of canal slopes shows that the damage of canal slopes of expansive soil (rock) is caused by crack and/or expansion. The monitoring of protection treatment shows that replacement ballasting treatment measure is effective in shallow instability of canal slopes, and water content decreases and fluctuates sensitively with the initial water content being affected by atmosphere. The relationship between suction and water content, the relationship between pore water pressure and water level, variation of earth pressure and other monitoring results are also studied .
Expansive soil (rock) has special engineering features. The canal slope of expansive soil is instable. It is difficult to deal with the canal slopes of expansive soil. The level of monitoring technology is higher. The selection, layout and laying technology of monitoring equipments as well as the monitoring methods of horizontal displacement, water content, suction, pore water pressure, earth pressure in the canal slopes of expansive soil (rock) are summarized. The stability monitoring of canal slopes shows that the damage of canal slopes of expansive soil (rock) is caused by crack and/or expansion. The monitoring of protection treatment shows that replacement ballasting treatment measure is effective in shallow instability of canal slopes, and water content decreases and fluctuates sensitively with the initial water content being affected by atmosphere. The relationship between suction and water content, the relationship between pore water pressure and water level, variation of earth pressure and other monitoring results are also studied .
Abstract：
A new true tri-axial apparatus has been developed by Shao Shengjun et al working in Xi’an University of Technology. In order to measure the mechanics property of unsaturated soils under the condition of three dimension principal stresses, the airproof framework of sample was improved by changing the shape of sample’s latex membrane and bottom and top plate of sample. Through adding the measuring instrument of porous water pressure and air pressure, the metric suction of unsaturated soils can be measured in the process of true tri-axial compression of unsaturated soils. The true tri-axial experiment of remold loess with water content 18%, dry density 1.35 g/cm3 was carried out under the condition of controlling the middle principal stress ratio b. The stress and strain curves of remold loess were obtained respectively under different confined pressure ( =50 kPa, 100 kPa, 150 kPa and 200 kPa) and middle principal stress ratio (b=0, 0.25, 0.5, 0.75 and 1.0). Based on the Bishop effective stress shear strength formula, the matric suction parameter of remold loess with water content 21% was determined by the direct shear tests. Appling the Bishop effective stress formula, the true tri-axial effective stress state at failure was described respectively on the and plane. The shear strength changing with uniform effective stress is linear approximately.
A new true tri-axial apparatus has been developed by Shao Shengjun et al working in Xi’an University of Technology. In order to measure the mechanics property of unsaturated soils under the condition of three dimension principal stresses, the airproof framework of sample was improved by changing the shape of sample’s latex membrane and bottom and top plate of sample. Through adding the measuring instrument of porous water pressure and air pressure, the metric suction of unsaturated soils can be measured in the process of true tri-axial compression of unsaturated soils. The true tri-axial experiment of remold loess with water content 18%, dry density 1.35 g/cm3 was carried out under the condition of controlling the middle principal stress ratio b. The stress and strain curves of remold loess were obtained respectively under different confined pressure ( =50 kPa, 100 kPa, 150 kPa and 200 kPa) and middle principal stress ratio (b=0, 0.25, 0.5, 0.75 and 1.0). Based on the Bishop effective stress shear strength formula, the matric suction parameter of remold loess with water content 21% was determined by the direct shear tests. Appling the Bishop effective stress formula, the true tri-axial effective stress state at failure was described respectively on the and plane. The shear strength changing with uniform effective stress is linear approximately.
Abstract：
Pile group foundations with elevated piles will be one of the most popular foundation types for large offshore wind turbines in the next few decades in China. Design of wind turbine foundations is of great importance for offshore wind farms, with the following several key issues involved: ① analysis of mechanical behaviors and deformation mechanisms of foundations under complicated combined loading; ② determination approach of foundation stiffness; ③ dynamic response analysis of foundations subjected to vessel collisions. A unified static and dynamic analysis model for elevated pile group foundations for offshore wind turbines is presented to address these issues mentioned above. Comparison between the calculated results and the test ones show that the present model can give good prediction on both small and large lateral deflection of piles, as well as the deformation of pile group foundations subjected to multi-axis complex loads. By introducing reasonable damping coefficients, the proposed model is also effective for vibration analysis of pile group foundations subjected to dynamic loads such as vessel impact loads.
Pile group foundations with elevated piles will be one of the most popular foundation types for large offshore wind turbines in the next few decades in China. Design of wind turbine foundations is of great importance for offshore wind farms, with the following several key issues involved: ① analysis of mechanical behaviors and deformation mechanisms of foundations under complicated combined loading; ② determination approach of foundation stiffness; ③ dynamic response analysis of foundations subjected to vessel collisions. A unified static and dynamic analysis model for elevated pile group foundations for offshore wind turbines is presented to address these issues mentioned above. Comparison between the calculated results and the test ones show that the present model can give good prediction on both small and large lateral deflection of piles, as well as the deformation of pile group foundations subjected to multi-axis complex loads. By introducing reasonable damping coefficients, the proposed model is also effective for vibration analysis of pile group foundations subjected to dynamic loads such as vessel impact loads.
Abstract：
The key technical problem of shallow treatment of super-soft ground is how to make the mud drainage consolidation as soon as possible, which has high water content and little bearing capacity. The traditional vacuum preloading process which is used for strengthening general soft ground is improved. A new vacuum preloading construction method without sand cushion, which fits reinforcement of the shallow foundation of fresh hydraulic fill mud, is proposed, and it is studied by field tests in Wenzhou Private Economic Development Zone. The transmission of vacuum pressure, surface settlement and pore pressure dissipation are studied. By comparing the physical and mechanical indicators as well as bearing capacity between reinforced foundation and fresh hydraulic fill mud, the results show that the consolidation effect of hydraulic fill layer is evident which meets the load requirements of the follow-up construction. A practical calculation method for increasing soil strength and bearing capacity, which fits the shallow treatment of super-soft ground, is proposed. It is successfully used to predict the reinforcing effects of large processing area.
The key technical problem of shallow treatment of super-soft ground is how to make the mud drainage consolidation as soon as possible, which has high water content and little bearing capacity. The traditional vacuum preloading process which is used for strengthening general soft ground is improved. A new vacuum preloading construction method without sand cushion, which fits reinforcement of the shallow foundation of fresh hydraulic fill mud, is proposed, and it is studied by field tests in Wenzhou Private Economic Development Zone. The transmission of vacuum pressure, surface settlement and pore pressure dissipation are studied. By comparing the physical and mechanical indicators as well as bearing capacity between reinforced foundation and fresh hydraulic fill mud, the results show that the consolidation effect of hydraulic fill layer is evident which meets the load requirements of the follow-up construction. A practical calculation method for increasing soil strength and bearing capacity, which fits the shallow treatment of super-soft ground, is proposed. It is successfully used to predict the reinforcing effects of large processing area.
Abstract：
Different seismic loads have important effect on loess subsidence. By means of the triaxial testing equipment, which is used to load random waves on specimen axially, undisturbed loess subsidence is comparatively studied under different seismic loads, and the effect of different seismic load on characters of loess subsidence is analyzed. The test indicates that the rasidual deformation of loess increases with the increase of dynamic stress under random seismic load or sine wave load, but the increase tendencies of them are different, which show that the characters of loess subsidence vary obviously under different seismic loads, and the effect of different seismic loads on the critical dynamic stress of loess subsidence is different, that is the critical dynamic stress is larger under the random seismic load than under sine wave load, and the effect of the random seismic load with different predominant periods, peaks and durations is also different, that is, the loess subsidence has relation with the predominant period, peak and duration of the random seismic load, and the effect of the predominant period is quite obvious.
Different seismic loads have important effect on loess subsidence. By means of the triaxial testing equipment, which is used to load random waves on specimen axially, undisturbed loess subsidence is comparatively studied under different seismic loads, and the effect of different seismic load on characters of loess subsidence is analyzed. The test indicates that the rasidual deformation of loess increases with the increase of dynamic stress under random seismic load or sine wave load, but the increase tendencies of them are different, which show that the characters of loess subsidence vary obviously under different seismic loads, and the effect of different seismic loads on the critical dynamic stress of loess subsidence is different, that is the critical dynamic stress is larger under the random seismic load than under sine wave load, and the effect of the random seismic load with different predominant periods, peaks and durations is also different, that is, the loess subsidence has relation with the predominant period, peak and duration of the random seismic load, and the effect of the predominant period is quite obvious.
Abstract：
Numerical model is adopted to simulate the soil arching effect of passive piles due to the lateral displacement of soil and some results of soil arching effect of passive piles are obtained. Based on the soil movement and stress transfer approach, soil pressure of the passive piles is calculated considering the soil arching effect at the passive side of piles and active wedge model at the active side of piles. Considering the real soil layer and soil arching effect in the passive side of piles and the stress transfer of pile shaft into the soil by means of dynamic strain wedge at the active side of piles, a global equilibrium equation is established and solved by use of the finite difference method. Finally, the proposed method is verified by an engineering example.
Numerical model is adopted to simulate the soil arching effect of passive piles due to the lateral displacement of soil and some results of soil arching effect of passive piles are obtained. Based on the soil movement and stress transfer approach, soil pressure of the passive piles is calculated considering the soil arching effect at the passive side of piles and active wedge model at the active side of piles. Considering the real soil layer and soil arching effect in the passive side of piles and the stress transfer of pile shaft into the soil by means of dynamic strain wedge at the active side of piles, a global equilibrium equation is established and solved by use of the finite difference method. Finally, the proposed method is verified by an engineering example.
Abstract：
The base post-grouting is used to improve the base resistance of piles, and the mechanism of base post-grouting in super-long piles needs to be a deep studied. In order to study the bearing capacity, static load tests are carried out on super-long bored piles employed in great bridges. The differences of the bearing capacity of super-long piled before and after base grouting are analyzed. Based on the test results, it is found that the bearing capacity of piles is increased by over 10 percent after base grouting. The frictional resistance at the lower part of piles increases significantly. As the load increases, the role of base grouting is more obvious. A comparative study between the field measured and calculated increments of the bearing capacity is made. The results indicate that the calculated increments of domestic standards are smaller than the field measured increments, and some calculated increments are over-conservative.
The base post-grouting is used to improve the base resistance of piles, and the mechanism of base post-grouting in super-long piles needs to be a deep studied. In order to study the bearing capacity, static load tests are carried out on super-long bored piles employed in great bridges. The differences of the bearing capacity of super-long piled before and after base grouting are analyzed. Based on the test results, it is found that the bearing capacity of piles is increased by over 10 percent after base grouting. The frictional resistance at the lower part of piles increases significantly. As the load increases, the role of base grouting is more obvious. A comparative study between the field measured and calculated increments of the bearing capacity is made. The results indicate that the calculated increments of domestic standards are smaller than the field measured increments, and some calculated increments are over-conservative.
Abstract：
The impact rolling is a kind of new technology in the area of ground treatment. Compared with the traditional rolling machines, it is more effective, the cost is lower, and it can treat thicker soil, especially it has obvious advantages in soft groud treatment. A new railway is under construction ， most of which are embankment on soft ground soil. The bearing capacity of the shallow natural foundation is less than 150 kPa, and it should be treated. Based on the pilot projects, the process and parameters of ground treatment are studied, and effects of ground treatment are tested. The conclusions may provide technical supports for the application of impact rolling in treatment of the whole line.
The impact rolling is a kind of new technology in the area of ground treatment. Compared with the traditional rolling machines, it is more effective, the cost is lower, and it can treat thicker soil, especially it has obvious advantages in soft groud treatment. A new railway is under construction ， most of which are embankment on soft ground soil. The bearing capacity of the shallow natural foundation is less than 150 kPa, and it should be treated. Based on the pilot projects, the process and parameters of ground treatment are studied, and effects of ground treatment are tested. The conclusions may provide technical supports for the application of impact rolling in treatment of the whole line.
Abstract：
The pile-net composite foundation with large diameter rigid piles is used in the tank for the first time. The design, simulation and optimization of the pile-net composite foundation are discussed. According to the calculation of the rigid pile-net composite foundation, it can substantially reduce the settlement and differential settlement of the tank base. On the basis of the preloading settlement monitoring, it is revealed that the results of three-dimensional finite element method are close to the actual test results. Soil pressure cells are installed on the top of the pile bearing stage and in soil between piles. According to the actual monitoring, the sharing ratio between piles and soil is calculated. Large-diameter rigid pile-net composite foundation, compared to the traditional pile-raft foundation, can save more than 60% of investment and more than 50% of time.
The pile-net composite foundation with large diameter rigid piles is used in the tank for the first time. The design, simulation and optimization of the pile-net composite foundation are discussed. According to the calculation of the rigid pile-net composite foundation, it can substantially reduce the settlement and differential settlement of the tank base. On the basis of the preloading settlement monitoring, it is revealed that the results of three-dimensional finite element method are close to the actual test results. Soil pressure cells are installed on the top of the pile bearing stage and in soil between piles. According to the actual monitoring, the sharing ratio between piles and soil is calculated. Large-diameter rigid pile-net composite foundation, compared to the traditional pile-raft foundation, can save more than 60% of investment and more than 50% of time.
Abstract：
The post-construction settlement of soft-soil roadbed is a serious hidden trouble to expressway. It is critical to control the deformation of soft-soil roadbed to optimize the construction speed and roadbed plan, to improve the construction quality and to ensure the project operation. The common prediction methods for post-construction settlement of soft-soil roadbed of expressway are qualitatively compared and analyzed. These methods include the Poisson,s model, grey model, genetic algorithm, neural network method, three-point method, curve fitting method and SFIA method. Finally, the SFIA method is selected to calculate the settlements of the second expressway of Beijing to Tianjin and the second expressway of Beijing International Airport. The calculated results are close to the actual values. For prediction of the post-construction settlement, soft-soil roadbed of expressway the roadbed construction process should be simulated, and the nonlinear soil modulus should be employed according to different construction loads.
The post-construction settlement of soft-soil roadbed is a serious hidden trouble to expressway. It is critical to control the deformation of soft-soil roadbed to optimize the construction speed and roadbed plan, to improve the construction quality and to ensure the project operation. The common prediction methods for post-construction settlement of soft-soil roadbed of expressway are qualitatively compared and analyzed. These methods include the Poisson,s model, grey model, genetic algorithm, neural network method, three-point method, curve fitting method and SFIA method. Finally, the SFIA method is selected to calculate the settlements of the second expressway of Beijing to Tianjin and the second expressway of Beijing International Airport. The calculated results are close to the actual values. For prediction of the post-construction settlement, soft-soil roadbed of expressway the roadbed construction process should be simulated, and the nonlinear soil modulus should be employed according to different construction loads.
Abstract：
Based on the reconstruction project of Tianjin-Tanggu Expressway, the subgrade bearing capacity of composite foundation with pipe piles is calculated. The Terzaghi's theory is verified, and the Terzaghi's theoretical formula is modified for application in composite pipe piles. Through the analysis of the typical elements, the stress model of pile-soil under rigid foundation is derived. Finally, it is demonstrated that the results from this solution are in accordance with the design ones of a project. So the proposed method can reflect the working behaviors of foundation treatment of pipes pile in Tianjin area. It supplements the application of composite foundation with pipe piles and prospects for the model.
Based on the reconstruction project of Tianjin-Tanggu Expressway, the subgrade bearing capacity of composite foundation with pipe piles is calculated. The Terzaghi's theory is verified, and the Terzaghi's theoretical formula is modified for application in composite pipe piles. Through the analysis of the typical elements, the stress model of pile-soil under rigid foundation is derived. Finally, it is demonstrated that the results from this solution are in accordance with the design ones of a project. So the proposed method can reflect the working behaviors of foundation treatment of pipes pile in Tianjin area. It supplements the application of composite foundation with pipe piles and prospects for the model.
Abstract：
The underground space project of Chen Clan Academy Cultural Square adjacent to world cultural heritage and urban rail transit lines is characterized by large excavation face, complex geological conditions and limited construction period. Based on the design and construction principles of safety, feasibility and rationality, different support structures for foundation pit are analyzed and compared. The top-down construction method featured with spun digging pile-lining wall interaction and basement floor system working as the horizontal interior bracing is elaborately designed. Through discussing uncertainties of the foundation pit, the reliability index on the basis of deformation of support structures is established, and the failure probability of support structures is calculated by Monte-Carlo FEM. The project is carried out safely and on schedule, satisfying the requirements put forward with the purpose of ensuring the 2010 Asian Games successfully held. It is indicated that pile-wall interaction with adverse construction as well as the relevant design parameters is reasonable and adequate to the support structures for the foundation pit of Chen Clan Academy Cultural Square.
The underground space project of Chen Clan Academy Cultural Square adjacent to world cultural heritage and urban rail transit lines is characterized by large excavation face, complex geological conditions and limited construction period. Based on the design and construction principles of safety, feasibility and rationality, different support structures for foundation pit are analyzed and compared. The top-down construction method featured with spun digging pile-lining wall interaction and basement floor system working as the horizontal interior bracing is elaborately designed. Through discussing uncertainties of the foundation pit, the reliability index on the basis of deformation of support structures is established, and the failure probability of support structures is calculated by Monte-Carlo FEM. The project is carried out safely and on schedule, satisfying the requirements put forward with the purpose of ensuring the 2010 Asian Games successfully held. It is indicated that pile-wall interaction with adverse construction as well as the relevant design parameters is reasonable and adequate to the support structures for the foundation pit of Chen Clan Academy Cultural Square.
Abstract：
The Tertiary and Cretaceous red-bed soft rock, widely spread in Changsha, Zhuzhou and Xiangtan, is composed of argillaceous gravellystone, silty mudstone and mudstone with the features of weak diagenetic process and susceptiable to weathering and easily be disingtegrated. The characteristics and corrosion mechanism of red bed in Tiyugongyuan Station in Changsha Metro Line No. 2 are studied based on the geological environment, distribution of soil strata, lithology characteristics and the substance by means of explorating, testing, X-ray technique, electricre sistivity and detecting resistivity . The results show that the development and distribution of corrosion in red bed are mainly influnced by the lithology features, geologic structure and groundwater. The construction risk of corrosion is analyzed, and the corresponding measures are put forward. It provides reference to the specific project and is of great significance for the construction of Changsha-Zhuzhou-Xiangtan economic integration.
The Tertiary and Cretaceous red-bed soft rock, widely spread in Changsha, Zhuzhou and Xiangtan, is composed of argillaceous gravellystone, silty mudstone and mudstone with the features of weak diagenetic process and susceptiable to weathering and easily be disingtegrated. The characteristics and corrosion mechanism of red bed in Tiyugongyuan Station in Changsha Metro Line No. 2 are studied based on the geological environment, distribution of soil strata, lithology characteristics and the substance by means of explorating, testing, X-ray technique, electricre sistivity and detecting resistivity . The results show that the development and distribution of corrosion in red bed are mainly influnced by the lithology features, geologic structure and groundwater. The construction risk of corrosion is analyzed, and the corresponding measures are put forward. It provides reference to the specific project and is of great significance for the construction of Changsha-Zhuzhou-Xiangtan economic integration.
Abstract：
At present, geotechnical engineers comprehensively study the stability and deformation and failure mechanism of natural steeply dipping bedding rock slopes, but it is not enough for the steeply dipping bedding high slopes under excavation works. Here, the researches on the slope structure character and deformation and failure mechanism of steeply dipping bedding high slope diseases are performed based on a treatment project for a actual steeply dipping bedding high slope. First of all, the character of deformation and failure for the slope and the slope structural features about steeply dipping bedding high slope disease are summarized. And then the stability factors, deformation and failure modes, stress state of the slope and four stages modes of deformation and failure of the steeply dipping bedding high slope disease are analyzed. On this basis, the deformation and failure mechanism of the steeply dipping bedding high slope disease is proposed. The results show that the slope structure of steeply dipping bedding high slope disease determines the development of deformation and failure mechanism, meanwhile under the effect of the external trigger factors, including excavation unloading and rainfall and so on, it will result in the slope damaged by the mode of bedding slip - crushing (collapse) sheared.
At present, geotechnical engineers comprehensively study the stability and deformation and failure mechanism of natural steeply dipping bedding rock slopes, but it is not enough for the steeply dipping bedding high slopes under excavation works. Here, the researches on the slope structure character and deformation and failure mechanism of steeply dipping bedding high slope diseases are performed based on a treatment project for a actual steeply dipping bedding high slope. First of all, the character of deformation and failure for the slope and the slope structural features about steeply dipping bedding high slope disease are summarized. And then the stability factors, deformation and failure modes, stress state of the slope and four stages modes of deformation and failure of the steeply dipping bedding high slope disease are analyzed. On this basis, the deformation and failure mechanism of the steeply dipping bedding high slope disease is proposed. The results show that the slope structure of steeply dipping bedding high slope disease determines the development of deformation and failure mechanism, meanwhile under the effect of the external trigger factors, including excavation unloading and rainfall and so on, it will result in the slope damaged by the mode of bedding slip - crushing (collapse) sheared.
Abstract：
The north abandoned lobe of the Yellow River Delta has become a kind of typical beach strongly eroded by waves after the Yellow River estuary changing to Qingshuigou flow path. However, the relationships between evolution characteristics and influencing factors of the beach erosion are not very clear to us. Accurate data about beach evolution were achieved by ten in-situ measurements which were taken from the abandoned lobe beach in the north of the Yellow River Delta from December 2008 to December 2009 meanwhile the weather and hydrology data were also collected. Based on these data, the beach evolution character and the relationships among influencing factors such as waves, storm tides, sea-level-rising, sea-ice and so on are analyzed. The results show that: (1) the north line of Yellow River Delta is at a strong-eroding state that the erosion rate can reach almost 56.6 cm per day and the erosion takes on a seasonal characteristic that the erosion is much stronger in spring and autumn; (2) the beach erosion-deposition process has a close connection with the hydrodynamic conditions that erosion and deposition appear alternately and a strong deposition can be caused by a storm tide surge; (3) sea level has the biggest rising rate while the beach erosion is not so obvious through which we can tell that the sea level rising has a little effect on beach erosion; (4) the sea ices which have a hydrodynamics-weakening function contribute a protective role in the beach; (5) the erosion-deposition process is not synchronous and does not just simply obey the law “erosion in winter and deposition in summer”.
The north abandoned lobe of the Yellow River Delta has become a kind of typical beach strongly eroded by waves after the Yellow River estuary changing to Qingshuigou flow path. However, the relationships between evolution characteristics and influencing factors of the beach erosion are not very clear to us. Accurate data about beach evolution were achieved by ten in-situ measurements which were taken from the abandoned lobe beach in the north of the Yellow River Delta from December 2008 to December 2009 meanwhile the weather and hydrology data were also collected. Based on these data, the beach evolution character and the relationships among influencing factors such as waves, storm tides, sea-level-rising, sea-ice and so on are analyzed. The results show that: (1) the north line of Yellow River Delta is at a strong-eroding state that the erosion rate can reach almost 56.6 cm per day and the erosion takes on a seasonal characteristic that the erosion is much stronger in spring and autumn; (2) the beach erosion-deposition process has a close connection with the hydrodynamic conditions that erosion and deposition appear alternately and a strong deposition can be caused by a storm tide surge; (3) sea level has the biggest rising rate while the beach erosion is not so obvious through which we can tell that the sea level rising has a little effect on beach erosion; (4) the sea ices which have a hydrodynamics-weakening function contribute a protective role in the beach; (5) the erosion-deposition process is not synchronous and does not just simply obey the law “erosion in winter and deposition in summer”.
2011, 33(zk1): 163-169.
Abstract：
The landslides of loess districts restrict the local economic development seriously. In order to reduce the loss caused by landslides, it is necessary to reinforce the analysis and prediction on loess slopes. The stability of high loess slopes is controlled by water content of slopes because of the water sensitivity of loess. In view of that, based on various influencing factors of loess slopes, a model is presented to predict the stability of loess slopes by simulating water content. Firstly, based on the graphic method, an automatic table lookup program is developed to generate numerous representative slope data, by using these data, a predicting model is established based on the modified genetic Neural Networks. Then the model is validated to be of high precision by simulating the training data and test data. Finally, taking two engineering cases for example, the application of the model in predicting the stability of slopes with different initial states is introduced. By comparing with the values of graphic method, the results show that the predicted results agree with the expected results, indicating that the model has wide applicability in Guanzhong area.
The landslides of loess districts restrict the local economic development seriously. In order to reduce the loss caused by landslides, it is necessary to reinforce the analysis and prediction on loess slopes. The stability of high loess slopes is controlled by water content of slopes because of the water sensitivity of loess. In view of that, based on various influencing factors of loess slopes, a model is presented to predict the stability of loess slopes by simulating water content. Firstly, based on the graphic method, an automatic table lookup program is developed to generate numerous representative slope data, by using these data, a predicting model is established based on the modified genetic Neural Networks. Then the model is validated to be of high precision by simulating the training data and test data. Finally, taking two engineering cases for example, the application of the model in predicting the stability of slopes with different initial states is introduced. By comparing with the values of graphic method, the results show that the predicted results agree with the expected results, indicating that the model has wide applicability in Guanzhong area.
Abstract：
Most researches related to loess mechanical properties highlight loess foundations and slopes, while little attention has been paid to loess tunnels. Several typical characteristics of loess both as a special soil and surrounding rock of loess tunnels, such as sensitivity to water content, failure at small strain, anisotropy, loess joints and its impact on stability of loess, are studied from the perspective of stability of tunnel and underground engineering. It is concluded that the existing methods and results associated with mechanical behaviours of loess can’t take the actual characteristics of loess into account when the loess behaves as surrounding rock of deep-buried tunnels. The necessary tests and corresponding methods are suggested mainly aimed at the surrounding rock classification of loess tunnels.
Most researches related to loess mechanical properties highlight loess foundations and slopes, while little attention has been paid to loess tunnels. Several typical characteristics of loess both as a special soil and surrounding rock of loess tunnels, such as sensitivity to water content, failure at small strain, anisotropy, loess joints and its impact on stability of loess, are studied from the perspective of stability of tunnel and underground engineering. It is concluded that the existing methods and results associated with mechanical behaviours of loess can’t take the actual characteristics of loess into account when the loess behaves as surrounding rock of deep-buried tunnels. The necessary tests and corresponding methods are suggested mainly aimed at the surrounding rock classification of loess tunnels.
2011, 33(zk1): 177-181.
Abstract：
A large-scale triaxial testing programme on materials of Jishixia Dam is presented by utilizing the 2000 kN static and dynamic triaxial apparatus in Tsinghua University. Firstly the main function and properties of the large-scale triaxial apparatus are expatiated, as well as the test materials and test method. A total of 6 groups of tests are conducted on main and sub rockfill materials of Jishixia Dam to study the stress-strain and volume-strain relation with different dry densities. The influences of porosity on the mechanics and deformation properties of rockfills are discussed. The results about the deformation behavior of rockfills are expected to provide experimental basis for engineering construction.
A large-scale triaxial testing programme on materials of Jishixia Dam is presented by utilizing the 2000 kN static and dynamic triaxial apparatus in Tsinghua University. Firstly the main function and properties of the large-scale triaxial apparatus are expatiated, as well as the test materials and test method. A total of 6 groups of tests are conducted on main and sub rockfill materials of Jishixia Dam to study the stress-strain and volume-strain relation with different dry densities. The influences of porosity on the mechanics and deformation properties of rockfills are discussed. The results about the deformation behavior of rockfills are expected to provide experimental basis for engineering construction.
Abstract：
With the construction and development of some large important projects, such as high-rise buildings, subways, earth dams and so on, deep foundation pit has been a critical question in geotechnical engineering. In unloading condition, the mechanical properties for a specified soil are the basis of determining parameters required to simulating analysis and design of deep foundation pit. For long time, parameters of shear strength of soil used in the design of foundation pit are obtained by means of the normal triaxial loading tests. Unloading condition in the excavation process is usually ignored. The research advances in soil behaviors under excavation unloading reported in the literature are reviewed. The research findings are summarized from the conventional triaxial unloading tests,<> K0 consolidated triaxial unloading tests and true triaxial tests. The existing problems and potential research topics in this field are put forward.
With the construction and development of some large important projects, such as high-rise buildings, subways, earth dams and so on, deep foundation pit has been a critical question in geotechnical engineering. In unloading condition, the mechanical properties for a specified soil are the basis of determining parameters required to simulating analysis and design of deep foundation pit. For long time, parameters of shear strength of soil used in the design of foundation pit are obtained by means of the normal triaxial loading tests. Unloading condition in the excavation process is usually ignored. The research advances in soil behaviors under excavation unloading reported in the literature are reviewed. The research findings are summarized from the conventional triaxial unloading tests,<> K0 consolidated triaxial unloading tests and true triaxial tests. The existing problems and potential research topics in this field are put forward.
Abstract：
The Hopfield neural network, with associative memory function, is used in the stability classification of adjoining rock of underground engineering. Five indexes, including rock quality designation ( RQD), uniaxial compressive strength ( Rw ), integrality coefficient ( K v ), strength coefficient of structural plane ( K f ) and seepage measurement of groundwater ( ω ), are selected as the factors which affect the classification. The function provided by matlab toolbox is used to build a network and for stimulation. After memorizing the standard of classification, a Hopfield network is established for the stability classification of adjoining rock of underground engineering. Then the network is used in the classification of the measured samples of two projects, Manwan Hydropower Station and Guangzhou Pumped Storage Power Station, to detect the classification ability of the network. The research shows that the classification results based on the Hopfield network are reliable. The network has a fast convergence rate and high practicability.
The Hopfield neural network, with associative memory function, is used in the stability classification of adjoining rock of underground engineering. Five indexes, including rock quality designation ( RQD), uniaxial compressive strength ( Rw ), integrality coefficient ( K v ), strength coefficient of structural plane ( K f ) and seepage measurement of groundwater ( ω ), are selected as the factors which affect the classification. The function provided by matlab toolbox is used to build a network and for stimulation. After memorizing the standard of classification, a Hopfield network is established for the stability classification of adjoining rock of underground engineering. Then the network is used in the classification of the measured samples of two projects, Manwan Hydropower Station and Guangzhou Pumped Storage Power Station, to detect the classification ability of the network. The research shows that the classification results based on the Hopfield network are reliable. The network has a fast convergence rate and high practicability.
Abstract：
In order to identify risk factors during the process of tunnel construction effectively, expert investigation method and analytic hierarchy process are combined to identify the risk in construction of large-span and shallow-buried highway tunnels based on the review of disadvantages of traditional risk recognition methods. The risk hierarchical structure for construction of Maoshan Mountain tunnel is established by using the analytic hierarchy process, and six basic risk events including surrounding rock instability, landslide of tunnel portal, overbreak, lining damage and leaking, tunnel top surface subsidence and influence of waste residue site on environment are obtained. The synthetic weight of each basic risk event is calculated, and the weight of surrounding rock instability related to the construction risk is close to 0.5. Therefore effective risk control measures are advised. It is concluded that analytic hierarchy process can act as a risk recognition model for construction of large-span and shallow-buried highway tunnels.
In order to identify risk factors during the process of tunnel construction effectively, expert investigation method and analytic hierarchy process are combined to identify the risk in construction of large-span and shallow-buried highway tunnels based on the review of disadvantages of traditional risk recognition methods. The risk hierarchical structure for construction of Maoshan Mountain tunnel is established by using the analytic hierarchy process, and six basic risk events including surrounding rock instability, landslide of tunnel portal, overbreak, lining damage and leaking, tunnel top surface subsidence and influence of waste residue site on environment are obtained. The synthetic weight of each basic risk event is calculated, and the weight of surrounding rock instability related to the construction risk is close to 0.5. Therefore effective risk control measures are advised. It is concluded that analytic hierarchy process can act as a risk recognition model for construction of large-span and shallow-buried highway tunnels.
Abstract：
A computational method to obtain displacement of soil slopes is presented. It is suggested how to determine the warning displacement and ultimate displacement. The main points of the method are: 1) for the local strength reduction method to obtain displacement fields of slopes under different strength reduction factors, it only reduces the strength of soils in the key region that is determinate to the slope stability, while the strength of other soils keep unchanged; 2) as a more accurate model, the variable modulus elasto-plastic model is used as constitutive model; 3) the reduced factor-displacement curve is divided into three deformation stages: the uniform deformation stage, the accelerated deformation stage and the unstable deformation stage. The displacement at the intersection point of the uniform and the accelerated deformation stages is considered to be warning displacement, and that of the accelerated and the unstable deformation stages is considered to be the ultimate displacement. Finally, the method is used in the analysis of an actual landslide. According to the reduction factor-displacement curve of the landslide, the reduction strength is very close to the strength of soils by in-situ push-shear tests, which illustrates that the proposed method is feasible to compute the displacement of soil slopes.
A computational method to obtain displacement of soil slopes is presented. It is suggested how to determine the warning displacement and ultimate displacement. The main points of the method are: 1) for the local strength reduction method to obtain displacement fields of slopes under different strength reduction factors, it only reduces the strength of soils in the key region that is determinate to the slope stability, while the strength of other soils keep unchanged; 2) as a more accurate model, the variable modulus elasto-plastic model is used as constitutive model; 3) the reduced factor-displacement curve is divided into three deformation stages: the uniform deformation stage, the accelerated deformation stage and the unstable deformation stage. The displacement at the intersection point of the uniform and the accelerated deformation stages is considered to be warning displacement, and that of the accelerated and the unstable deformation stages is considered to be the ultimate displacement. Finally, the method is used in the analysis of an actual landslide. According to the reduction factor-displacement curve of the landslide, the reduction strength is very close to the strength of soils by in-situ push-shear tests, which illustrates that the proposed method is feasible to compute the displacement of soil slopes.
Abstract：
The main difference of stability evaluation between the mountainous highway exhibition subgrade and the ordinary subgrade lies in the interacting distortion of various highway subgrades. Namely the partial subgrade deformation initiates the deformations of nearby subgrade and even the entire subgrade around a mountainous section. Meanwhile the interaction matrix especially qualifies to solve complex questions concernign interactions and mutual coupling of various factors. The interaction matrix is introduced to establish a stability evaluation method which is possible to consider the basic parameters of highway exhibition subgrade and the mutual influence among variables, that is the coordinated method of highway exhibition. This method is used to evaluate the stability of a highway exhibition subgrade and slope system that contains two roads. In the overall evaluation all informations about engineering design, construction and operation of this system are considered. The method considers influences of each parameter on the overall system and the contribution of parametric interaction to the overall system.
The main difference of stability evaluation between the mountainous highway exhibition subgrade and the ordinary subgrade lies in the interacting distortion of various highway subgrades. Namely the partial subgrade deformation initiates the deformations of nearby subgrade and even the entire subgrade around a mountainous section. Meanwhile the interaction matrix especially qualifies to solve complex questions concernign interactions and mutual coupling of various factors. The interaction matrix is introduced to establish a stability evaluation method which is possible to consider the basic parameters of highway exhibition subgrade and the mutual influence among variables, that is the coordinated method of highway exhibition. This method is used to evaluate the stability of a highway exhibition subgrade and slope system that contains two roads. In the overall evaluation all informations about engineering design, construction and operation of this system are considered. The method considers influences of each parameter on the overall system and the contribution of parametric interaction to the overall system.
2011, 33(zk1): 207-210.
Abstract：
Stepped soil-nail wall is formed by setting a platform in the middle part of a typical soil-nail wall. Due to the presence of the platform, the earth pressure distribution of the stepped soil-nail wall is changed, and the stress state and strain of soil are also changed. Compared with those of the typical soil-nail wall, the deformation and soil-nail internal force of the sepped soil-nail wall are smaller, and the stability is higher. Both the position and width of the platform influence the behavior of the stepped soil-nail wall. According to the numerical calculation and engineering experience, for homogenous soil slopes, the position of platform is suggested to be placed at a depth whick is 0.6 times the foundation pit. For the slope with weak interlayer, the flatform is suggested to be set on the top surface of the weak interlayer. The step width is suggested to be not less than 0.1 times the depth of foundation pit. Through a practical engineering example, the general behaviour of both the typical soil-nail wall and the stepped soil-nail are compared. It is demonstrated that both the horizontal displacement and the nail force of the stepped soil-nail wall are smaller than those of the typical soil-nail wall, and the stability of the former is higher.
Stepped soil-nail wall is formed by setting a platform in the middle part of a typical soil-nail wall. Due to the presence of the platform, the earth pressure distribution of the stepped soil-nail wall is changed, and the stress state and strain of soil are also changed. Compared with those of the typical soil-nail wall, the deformation and soil-nail internal force of the sepped soil-nail wall are smaller, and the stability is higher. Both the position and width of the platform influence the behavior of the stepped soil-nail wall. According to the numerical calculation and engineering experience, for homogenous soil slopes, the position of platform is suggested to be placed at a depth whick is 0.6 times the foundation pit. For the slope with weak interlayer, the flatform is suggested to be set on the top surface of the weak interlayer. The step width is suggested to be not less than 0.1 times the depth of foundation pit. Through a practical engineering example, the general behaviour of both the typical soil-nail wall and the stepped soil-nail are compared. It is demonstrated that both the horizontal displacement and the nail force of the stepped soil-nail wall are smaller than those of the typical soil-nail wall, and the stability of the former is higher.
Abstract：
By analyzing the simulated temperature field of frozen-soil foundation with embankment in different structures, the embankment cooling effect and some important factors and their relationship are studied. The factors include embankment structure, temperature in block-stone layer, convection Rayleigh number ( Ra) and the critical Rayleigh number ( Ra c ) of different convection patterns. The research results show that the air convection pattern of block-stone in winter is the most important key factors influencing the cooling effect of embankment, and the block-stone embankment structure in which the air convection patterns are mainly (1,1) and (2,1) in winter has the strongest cooling effect on frozen soil foundation.
By analyzing the simulated temperature field of frozen-soil foundation with embankment in different structures, the embankment cooling effect and some important factors and their relationship are studied. The factors include embankment structure, temperature in block-stone layer, convection Rayleigh number ( Ra) and the critical Rayleigh number ( Ra c ) of different convection patterns. The research results show that the air convection pattern of block-stone in winter is the most important key factors influencing the cooling effect of embankment, and the block-stone embankment structure in which the air convection patterns are mainly (1,1) and (2,1) in winter has the strongest cooling effect on frozen soil foundation.
Abstract：
During the construction of deep foundation pits of subway, because of the engineering geological conditions and environment, the deformation rules of the deep foundation pits greatly differ. A deep foundation pit is taken as an example. Based on the actual monitoring data of the deformation of row pile retaining structures, the deformation rules of the retaining structure s during every construction stage of the deep foundation pit are analyzed by means of numerical simulations. The results indicate that at the beginning of excavating the foundation pit, the curve of retaining piles linearly changes. With the excavation of foundation pit and the erection of steel braces, the curve is in the shape of bow. The maximum horizontal displacement happens at the 2/3 depth of the pit. It can provide the reference for the optimization design and scientific construction of similar deep foundation pits.
During the construction of deep foundation pits of subway, because of the engineering geological conditions and environment, the deformation rules of the deep foundation pits greatly differ. A deep foundation pit is taken as an example. Based on the actual monitoring data of the deformation of row pile retaining structures, the deformation rules of the retaining structure s during every construction stage of the deep foundation pit are analyzed by means of numerical simulations. The results indicate that at the beginning of excavating the foundation pit, the curve of retaining piles linearly changes. With the excavation of foundation pit and the erection of steel braces, the curve is in the shape of bow. The maximum horizontal displacement happens at the 2/3 depth of the pit. It can provide the reference for the optimization design and scientific construction of similar deep foundation pits.
Abstract：
It is necessary to monitor the settlement during construction of highways in the soft clay ground because of its characteristics of high compressibility and low strength. The settlement data during the time of filling and surcharge correspond with the geological data of the thick soft soil. They show that the plan of surcharge is necessary, and the effectiveness of the surcharge is obvious. The data also show both the large soil deformation and the high settlement velocity. Slow convergence have negtive effect on the actual surcharge, and it will lead to large settlement at late stage, which is not corresponding to that of the silty clay with middle to high compressibilities. Therefore, other plans are put forward to meet the control requirements.
It is necessary to monitor the settlement during construction of highways in the soft clay ground because of its characteristics of high compressibility and low strength. The settlement data during the time of filling and surcharge correspond with the geological data of the thick soft soil. They show that the plan of surcharge is necessary, and the effectiveness of the surcharge is obvious. The data also show both the large soil deformation and the high settlement velocity. Slow convergence have negtive effect on the actual surcharge, and it will lead to large settlement at late stage, which is not corresponding to that of the silty clay with middle to high compressibilities. Therefore, other plans are put forward to meet the control requirements.
Abstract：
Based on the field observation of wind-blown sand mothion in "100-kilometer wind area" along the Lanzhou-Urumqi Railway, the fresh gales mainly concentrate in spring and summer. The speed of sand-raising wind is for larger than that in desert regions, approximately 9-class wind. The sand transport capacity increases with the height of the wind, which has a good agreement with the experimental results. The sand transport capacity is up to almost 80% of the total capacity below 2 meters. The results of sand particle size analysis show that the form of wind-blown sand motion is bound and peristalsis below 3 meters, and it is mostly suspending over 3 meters.
Based on the field observation of wind-blown sand mothion in "100-kilometer wind area" along the Lanzhou-Urumqi Railway, the fresh gales mainly concentrate in spring and summer. The speed of sand-raising wind is for larger than that in desert regions, approximately 9-class wind. The sand transport capacity increases with the height of the wind, which has a good agreement with the experimental results. The sand transport capacity is up to almost 80% of the total capacity below 2 meters. The results of sand particle size analysis show that the form of wind-blown sand motion is bound and peristalsis below 3 meters, and it is mostly suspending over 3 meters.
2011, 33(zk1): 227-229.
Abstract：
Researches and applications of low-energy DCM tests in the weak foundations expand the application field of DCM, while making an extra options for soft ground treatment. The low energy DCM is successfully put into practice in the soft soil subgrade. The settlements of the surface and in and outside the test area and the growth and dissipation of pore water pressure at different depths in the test area are monitored. A 1 m2 loading plate is applied, and the shallow bearing capacity of design is verified. The results show that the low-energy DCM mainly affects the engineering properties of shallow soft soil, and the excess pore pressure dissipation lasts about 5 ~ 15 d, which is caused by dynamic compaction. Because of the low level energy, the construction of dynamic compaction has little effect on the surrounding environment. And it can meet the capacity requirements of soft subgrade.
Researches and applications of low-energy DCM tests in the weak foundations expand the application field of DCM, while making an extra options for soft ground treatment. The low energy DCM is successfully put into practice in the soft soil subgrade. The settlements of the surface and in and outside the test area and the growth and dissipation of pore water pressure at different depths in the test area are monitored. A 1 m2 loading plate is applied, and the shallow bearing capacity of design is verified. The results show that the low-energy DCM mainly affects the engineering properties of shallow soft soil, and the excess pore pressure dissipation lasts about 5 ~ 15 d, which is caused by dynamic compaction. Because of the low level energy, the construction of dynamic compaction has little effect on the surrounding environment. And it can meet the capacity requirements of soft subgrade.
Abstract：
The settlement and deformation in the soft foundation of Pengze-Hukou Highway during construction process are taken as the research object. The monitoring programme on the soft foundation is discussed. The observed data of settlement of subgrade show that the filling interval has some effect on the settlement. Analytic results indicate that longer filling interval time will extend the consolidation process of subgrade, but it can reduce the total settlement and the horizontal displacement of embankment toe.
The settlement and deformation in the soft foundation of Pengze-Hukou Highway during construction process are taken as the research object. The monitoring programme on the soft foundation is discussed. The observed data of settlement of subgrade show that the filling interval has some effect on the settlement. Analytic results indicate that longer filling interval time will extend the consolidation process of subgrade, but it can reduce the total settlement and the horizontal displacement of embankment toe.
Abstract：
More and more ultra soft soil improvement projects need to be executed at present in China. Based on some improvements of the traditional vacuum preloading method, a new technology for improving the surface-layer of the ultra soft soil by vacuum preloading is developed. The recyclable three-dimensional drainage cushion made of polythene is used to replace the sand cushion, which solves the laying problem of the sand cushion on the ultra soft soil and can be a solution of the continuous increasing of the cost in vacuum preloading projects owing to the increasing price of the natural sand. The plate of foam plastic is used to construct the float bridge, which provides a steady platform for the transportation of construction materials. The water-stop dike is built along the float bridge, which can also divide the wide area of ultra soft soil ground into several portions for improvement. Woven fabrics and non-woven fabrics are laid on the surface of the ultra soft soil, which can provide the platform for the installation of the prefabricated vertical drain. A typical application project is given to illustrate this technology.
More and more ultra soft soil improvement projects need to be executed at present in China. Based on some improvements of the traditional vacuum preloading method, a new technology for improving the surface-layer of the ultra soft soil by vacuum preloading is developed. The recyclable three-dimensional drainage cushion made of polythene is used to replace the sand cushion, which solves the laying problem of the sand cushion on the ultra soft soil and can be a solution of the continuous increasing of the cost in vacuum preloading projects owing to the increasing price of the natural sand. The plate of foam plastic is used to construct the float bridge, which provides a steady platform for the transportation of construction materials. The water-stop dike is built along the float bridge, which can also divide the wide area of ultra soft soil ground into several portions for improvement. Woven fabrics and non-woven fabrics are laid on the surface of the ultra soft soil, which can provide the platform for the installation of the prefabricated vertical drain. A typical application project is given to illustrate this technology.
Abstract：
The maintenance after the construction of slope reinforcing projects is always a focal and difficult point in the daily maintenance of expressways. As the new patent technologies used in slope reinforcing projects in recent years, the stress detection and compensation after the construction of anchor cables have been gradually adopted in the daily maintenance of slope reinforcing projects. The new two technologies are applied in the left-side slope of an expressway at the range of K3457+744 to K3458+144. It can be used as the reference for the similar projects in the future.
The maintenance after the construction of slope reinforcing projects is always a focal and difficult point in the daily maintenance of expressways. As the new patent technologies used in slope reinforcing projects in recent years, the stress detection and compensation after the construction of anchor cables have been gradually adopted in the daily maintenance of slope reinforcing projects. The new two technologies are applied in the left-side slope of an expressway at the range of K3457+744 to K3458+144. It can be used as the reference for the similar projects in the future.
2011, 33(zk1): 242-245.
Abstract：
According to the original data of dynamic compaction tests, the relation model of settlement and ramming numbers is established. The pattern of settlement changing with ramming numbers is outlined. Based on the dissipative structure theory for deformation of geotechnical materials, the effect of tamping energy on enhancing the orderliness and stability of the backfill layers open system is analyzed in the view of energy. The laws of the effective evolving function denoted by tamping energy changing with increasing ramming numbers are discussed. The results indicate: (1) the laws of single ramming settlement associated with increasing ramming numbers can be divided into two stages; (2) the original thickness of loose backfill layers influences the numbers, which is required to converge the single ramming settlement curve, but has little impact on the ultimate converge value; (3) with the improvement of system orderliness and stability, the tamping energy which accounts for keeping and promoting the system orderliness and stability decreases, while divergence and transfer energy increases, and the system tends to a relatively stable state associated with the tamping energy.
According to the original data of dynamic compaction tests, the relation model of settlement and ramming numbers is established. The pattern of settlement changing with ramming numbers is outlined. Based on the dissipative structure theory for deformation of geotechnical materials, the effect of tamping energy on enhancing the orderliness and stability of the backfill layers open system is analyzed in the view of energy. The laws of the effective evolving function denoted by tamping energy changing with increasing ramming numbers are discussed. The results indicate: (1) the laws of single ramming settlement associated with increasing ramming numbers can be divided into two stages; (2) the original thickness of loose backfill layers influences the numbers, which is required to converge the single ramming settlement curve, but has little impact on the ultimate converge value; (3) with the improvement of system orderliness and stability, the tamping energy which accounts for keeping and promoting the system orderliness and stability decreases, while divergence and transfer energy increases, and the system tends to a relatively stable state associated with the tamping energy.
Abstract：
The dynamic compaction is a common technology for ground treatment. Based on the tests on dynamic compaction vibration at test site of ground treatment project of a company’s second stage filled area, the attenuation relation between acceleration of dynamic compaction vibration and measuring point distance is analyzed. While the attenuation relation between speed of dynamic compaction vibration and measuring point distance is also analyzed. The relation between level of dynamic compaction, vibration acceleration and speed at measuring points are studied. The relation between number of compacting, vibration acceleration and speed at measuring points are also studied. The roles of vibration isolation trenches are evaluated. The test site is divided into different vibration coverage zones (vibration vulnerable zone, basic safe zone, safe zone) according to corresponding standards. The grounds and structures of buildings are combined to put forward the proposals for construction and improvement of dynamic compaction.
The dynamic compaction is a common technology for ground treatment. Based on the tests on dynamic compaction vibration at test site of ground treatment project of a company’s second stage filled area, the attenuation relation between acceleration of dynamic compaction vibration and measuring point distance is analyzed. While the attenuation relation between speed of dynamic compaction vibration and measuring point distance is also analyzed. The relation between level of dynamic compaction, vibration acceleration and speed at measuring points are studied. The relation between number of compacting, vibration acceleration and speed at measuring points are also studied. The roles of vibration isolation trenches are evaluated. The test site is divided into different vibration coverage zones (vibration vulnerable zone, basic safe zone, safe zone) according to corresponding standards. The grounds and structures of buildings are combined to put forward the proposals for construction and improvement of dynamic compaction.
Abstract：
The Qarhan-Golmud Highway of Qinghai Province is located in cold region of Qinghai-Tibet Plateau and salt lake region. The mechanical properties of saline soils varly with moisture and climate, which will influence the project construction. The gravel piles formed by the dynamic compaction replacement are applied in composite foundation of saline soils, and field tests are carried out in this region. It provides methods for determining the coefficients of the capacity and deformation modulus of composite foundation with the gravel piles formed by the dynamic compaction replacement. The calculated values are analyzed, and they meet the met design requirements. At the same time, the strength and working mechanism of pile-soil and settlement reduction of the composite foundation are analyzed after reinforcement. The reinforcement case of dynamic compaction replacement has good reinforcement effects in saline soils of salt lake region, which helps the migration of water and salt and reduces foundation settlement in saline soils.
The Qarhan-Golmud Highway of Qinghai Province is located in cold region of Qinghai-Tibet Plateau and salt lake region. The mechanical properties of saline soils varly with moisture and climate, which will influence the project construction. The gravel piles formed by the dynamic compaction replacement are applied in composite foundation of saline soils, and field tests are carried out in this region. It provides methods for determining the coefficients of the capacity and deformation modulus of composite foundation with the gravel piles formed by the dynamic compaction replacement. The calculated values are analyzed, and they meet the met design requirements. At the same time, the strength and working mechanism of pile-soil and settlement reduction of the composite foundation are analyzed after reinforcement. The reinforcement case of dynamic compaction replacement has good reinforcement effects in saline soils of salt lake region, which helps the migration of water and salt and reduces foundation settlement in saline soils.
Abstract：
The crustal structure beneath the temporary seismic array is imaged with teleseismic receiver functions in Tianshui earthquake-prone area in the northeast margin of Qinghai-Tibet Plateau. The results indicate that the Lueyang-Diebu fault and the north margin of West Qinling Mountains fault are ultra-crust faults which penetrate the Moho and lead to the weakness of impendence-contrast of Moho. The earthquakes in this area often nucleate in the margin region with sharp variety of the velocity, and the huge earthquakes in history might occurred near the asperity resulting from the interaction between faults and Conrad discontinuity at the depth of about 20 km .
The crustal structure beneath the temporary seismic array is imaged with teleseismic receiver functions in Tianshui earthquake-prone area in the northeast margin of Qinghai-Tibet Plateau. The results indicate that the Lueyang-Diebu fault and the north margin of West Qinling Mountains fault are ultra-crust faults which penetrate the Moho and lead to the weakness of impendence-contrast of Moho. The earthquakes in this area often nucleate in the margin region with sharp variety of the velocity, and the huge earthquakes in history might occurred near the asperity resulting from the interaction between faults and Conrad discontinuity at the depth of about 20 km .
2011, 33(zk1): 261-265.
Abstract：
During the construction of remote highways, the disaster of landslide transformed from faulted rock mass often occurs. The landslide translated from the faulted rock mass is quite harmful to highway construction, and the control cost is very high. First, the deforming progress and mechanics, monitoring and stability after transformation are analyzed and discussed. Then the best proposal is adopted and the landslide is successfully controlled. Finally, the valuable experience and lessons are gained, and the inter-transform modes and influencing factors of the ancient faulted rock mass in layered, sheet and tabular anti-dip rock section, transforming into cutting-layer rock landslide, are summarized. It will give important instructions for treating disasters like this during the highway construction in the future.
During the construction of remote highways, the disaster of landslide transformed from faulted rock mass often occurs. The landslide translated from the faulted rock mass is quite harmful to highway construction, and the control cost is very high. First, the deforming progress and mechanics, monitoring and stability after transformation are analyzed and discussed. Then the best proposal is adopted and the landslide is successfully controlled. Finally, the valuable experience and lessons are gained, and the inter-transform modes and influencing factors of the ancient faulted rock mass in layered, sheet and tabular anti-dip rock section, transforming into cutting-layer rock landslide, are summarized. It will give important instructions for treating disasters like this during the highway construction in the future.
Abstract：
The s hield tunneling method is a common construction one for underground tunnel s widely used in soft soils . B ut people still lack adequate knowledge and engineering experience on the reasons and mechanism of soft soil movement and ground settlement caused by the excavation of shield tunneling, which needs further investigation. Hence, take n the excavation of the subway internal tunnel of Hangzhou Metro Line No. 1 for an example, three-dimensional nonlinear finite element simulation and analysis are made on the excavation process of metro tunnel shield by using numerical methods. The curves of ground movement and settlement of soils around the tunnel caused by shield construction are acquired. The variation rules of transverse and longitudinal ground settlements caused by shield construction as well as the trend and distribution of the settlement s at different depths are obtained and analyzed. Some useful conclusions are drawn for the design and construction of metro tunnel s in soft soil area.
The s hield tunneling method is a common construction one for underground tunnel s widely used in soft soils . B ut people still lack adequate knowledge and engineering experience on the reasons and mechanism of soft soil movement and ground settlement caused by the excavation of shield tunneling, which needs further investigation. Hence, take n the excavation of the subway internal tunnel of Hangzhou Metro Line No. 1 for an example, three-dimensional nonlinear finite element simulation and analysis are made on the excavation process of metro tunnel shield by using numerical methods. The curves of ground movement and settlement of soils around the tunnel caused by shield construction are acquired. The variation rules of transverse and longitudinal ground settlements caused by shield construction as well as the trend and distribution of the settlement s at different depths are obtained and analyzed. Some useful conclusions are drawn for the design and construction of metro tunnel s in soft soil area.
Abstract：
Based on the successful engineering practice for the underground garage of a hospital in Shanghai, the design and practice for the underground garage under the congested urban housing environment in Shanghai soft soil area are presented. The garage is close to nine existing buildings including two historical buildings whose protection requirements are extremely high. According to the characteristics of the project, the temporary retaining and bracing system combined with the substructure of the underground garage and the top-down construction method are adopted. Precast diaphragm walls first applied in two-storey underground garage in Shanghai soft soil are used as the temporary retaining wall combined with the exterior wall of the garage . In order to reduce the settlement of buildings caused by deep excavation, protective measures including shut-off screens between the retaining wall and the existing buildings and the pile underpinning technique for the foundation of the existing buildings are applied. The practice shows that the settlement of the buildings meets the requirements through adopting the above-mentioned technical measures, and the safety of the surrounding environment is ensured. This project provides a reference for other similar underground space development projects in Shanghai area.
Based on the successful engineering practice for the underground garage of a hospital in Shanghai, the design and practice for the underground garage under the congested urban housing environment in Shanghai soft soil area are presented. The garage is close to nine existing buildings including two historical buildings whose protection requirements are extremely high. According to the characteristics of the project, the temporary retaining and bracing system combined with the substructure of the underground garage and the top-down construction method are adopted. Precast diaphragm walls first applied in two-storey underground garage in Shanghai soft soil are used as the temporary retaining wall combined with the exterior wall of the garage . In order to reduce the settlement of buildings caused by deep excavation, protective measures including shut-off screens between the retaining wall and the existing buildings and the pile underpinning technique for the foundation of the existing buildings are applied. The practice shows that the settlement of the buildings meets the requirements through adopting the above-mentioned technical measures, and the safety of the surrounding environment is ensured. This project provides a reference for other similar underground space development projects in Shanghai area.
Abstract：
When the metro is in operation, there are increasing longitudinal nonuniform settlements of shield tunnels due to various interior and exterior causes. Therefore, some expansion of shield tunnel segment joints develops in varying degree and the water resistance deteriorates. By using the 4th order B-spline interpolation curve to fit monitoring data and calculate additional longitudinal curvature, the degree of nonuniform settlements can be accurately reflected. Then considering the additional curvature radius, geometrical dimension of segment and longitudinal stiffness ratio, that means aleatory uncertainty and epistemic uncertainty are all considered, an interval Monte Carlo method at different levels of significance is developed to estimate the probability of shield tunnel segment joint failure. Grading the upper bound of the failure probability using four level assessments can directly reflect the operational performance of the segment joints. Inspection and evaluation results are compared and show good consistency. It is proved that the proposed method can provide guidance for the maintenance of shield tunnels in soft soils.
When the metro is in operation, there are increasing longitudinal nonuniform settlements of shield tunnels due to various interior and exterior causes. Therefore, some expansion of shield tunnel segment joints develops in varying degree and the water resistance deteriorates. By using the 4th order B-spline interpolation curve to fit monitoring data and calculate additional longitudinal curvature, the degree of nonuniform settlements can be accurately reflected. Then considering the additional curvature radius, geometrical dimension of segment and longitudinal stiffness ratio, that means aleatory uncertainty and epistemic uncertainty are all considered, an interval Monte Carlo method at different levels of significance is developed to estimate the probability of shield tunnel segment joint failure. Grading the upper bound of the failure probability using four level assessments can directly reflect the operational performance of the segment joints. Inspection and evaluation results are compared and show good consistency. It is proved that the proposed method can provide guidance for the maintenance of shield tunnels in soft soils.
2011, 33(zk1): 284-291.
Abstract：
Based on a deep foundation pit of metro in Beijing, the geological conditions of the proposed field, structural types and construction process are introduced. According to the monitoring results in the construction process, the variations of the displacement of fender piles, axial force of the steel supports and surface settlement are analyzed. The results of the numerical simulation are compared with those of finite element software, and they are almost consistent. Through further researches, the effects of pit size, embedded depth of the piles and construction condition on the deformation rules of deep foundation pit are obtained. It can provide a reference for the design and construction of deep foundation pits under this type of support.
Based on a deep foundation pit of metro in Beijing, the geological conditions of the proposed field, structural types and construction process are introduced. According to the monitoring results in the construction process, the variations of the displacement of fender piles, axial force of the steel supports and surface settlement are analyzed. The results of the numerical simulation are compared with those of finite element software, and they are almost consistent. Through further researches, the effects of pit size, embedded depth of the piles and construction condition on the deformation rules of deep foundation pit are obtained. It can provide a reference for the design and construction of deep foundation pits under this type of support.
Abstract：
The microstructure fractal of sliding zone soil of Suoertou landslide is studied. The sliding zone soil is tested for physical-mechanical properties through the laboratory tests, then by use of the scan electronic microscope technique (SEM), the image-processing-analysis and computer-vision technique, the microstructure fractal parameters of soil pores are extracted based on the fractal geometry and the perimeter-area method. The influences of the threshold and magnification on the quantitative results of soil microstructure are investigated, and the standard of image processing is determined according to them. The results show that the sliding zone soil of Suoertou landslide is marked by fractal. Finally the relationship among fractal dimension, void ratio and shear strength of soil is expounded, indicating that the shear strength increases and the void ratio decreases with the increase of the fractal dimension, and vice versa. It provides a reference basis for forecasting the mechanical behaviors of soil by its microstructure fractal parameters.
The microstructure fractal of sliding zone soil of Suoertou landslide is studied. The sliding zone soil is tested for physical-mechanical properties through the laboratory tests, then by use of the scan electronic microscope technique (SEM), the image-processing-analysis and computer-vision technique, the microstructure fractal parameters of soil pores are extracted based on the fractal geometry and the perimeter-area method. The influences of the threshold and magnification on the quantitative results of soil microstructure are investigated, and the standard of image processing is determined according to them. The results show that the sliding zone soil of Suoertou landslide is marked by fractal. Finally the relationship among fractal dimension, void ratio and shear strength of soil is expounded, indicating that the shear strength increases and the void ratio decreases with the increase of the fractal dimension, and vice versa. It provides a reference basis for forecasting the mechanical behaviors of soil by its microstructure fractal parameters.
2011, 33(zk1): 298-301.
Abstract：
The California bearing ratio (CBR) is an important index to evaluate the performances of the subgrade and pavement materials in expressways. Generally, the CBR<> value of clay is not enough for design and construction. Lime is an effective and commonly used admixture that can remarkably improve the physical and mechanical properties and strength of the clay. In order to study the influence of lime content on the CBR value, series of physical and mechanical tests on the clay from an expressway in Jiangsu are carried out. Based on the tests results, the influences of the lime content on the physical and mechanical properties of the clay are analyzed. The variaton rules of the CBR value and the main influence factors are also discussed.
The California bearing ratio (CBR) is an important index to evaluate the performances of the subgrade and pavement materials in expressways. Generally, the CBR<> value of clay is not enough for design and construction. Lime is an effective and commonly used admixture that can remarkably improve the physical and mechanical properties and strength of the clay. In order to study the influence of lime content on the CBR value, series of physical and mechanical tests on the clay from an expressway in Jiangsu are carried out. Based on the tests results, the influences of the lime content on the physical and mechanical properties of the clay are analyzed. The variaton rules of the CBR value and the main influence factors are also discussed.
Abstract：
Dredged filling as a low-cost, pollution-free, double-effective method of land reclamation, has been widely applied in the offshore areas. Then, the improvement of double-layered ground composed by dredged fill and marine mud has been becoming a hot spot concerned by geotechnical engineers. The probability and statistics theory is introduced into the analysis of the double-layered sand-drained ground consolidation. The influences of the uncertainty of geotechnical parameters and the correlative distance of soil are studied. Under the horizontal coefficient of consolidation being a gamma distribution, the computational formulas of the expectation and variance of consolidation degree for double-layered sand-drained ground are obtained. The Monte Carlo simulation method is used to analyze the average consolidation degree for double-layered sand-drained ground in a project in Shenzhen. The results show that the preloading time calculated by the deterministic method can not meet the requirements of the project, and the probabilistic analysis is more reasonable.
Dredged filling as a low-cost, pollution-free, double-effective method of land reclamation, has been widely applied in the offshore areas. Then, the improvement of double-layered ground composed by dredged fill and marine mud has been becoming a hot spot concerned by geotechnical engineers. The probability and statistics theory is introduced into the analysis of the double-layered sand-drained ground consolidation. The influences of the uncertainty of geotechnical parameters and the correlative distance of soil are studied. Under the horizontal coefficient of consolidation being a gamma distribution, the computational formulas of the expectation and variance of consolidation degree for double-layered sand-drained ground are obtained. The Monte Carlo simulation method is used to analyze the average consolidation degree for double-layered sand-drained ground in a project in Shenzhen. The results show that the preloading time calculated by the deterministic method can not meet the requirements of the project, and the probabilistic analysis is more reasonable.
Abstract：
With the rapid development of basic communication construction in China, basic road construction is steadily increasing. The miles of roads increase and the grade of roads goes higher. In order to raise transport speed and efficiency, the line selection and road construction gradually extend from plain areas to hilly and mountainous areas, and consequently the problem of slope disasters is increasing. A brief introduction of roadbed diseases in Huangnan district of Qinghai Province is given. In a case study, the distribution of disease area, characteristics of deformation, causes of diseases, scale of diseases, tendency of disease development, degree of dangerousness and hazard extent are analyzed and studied. After a comprehensive analysis of the causes of deformation, the corresponding control measures are presented and are proved to be effective.
With the rapid development of basic communication construction in China, basic road construction is steadily increasing. The miles of roads increase and the grade of roads goes higher. In order to raise transport speed and efficiency, the line selection and road construction gradually extend from plain areas to hilly and mountainous areas, and consequently the problem of slope disasters is increasing. A brief introduction of roadbed diseases in Huangnan district of Qinghai Province is given. In a case study, the distribution of disease area, characteristics of deformation, causes of diseases, scale of diseases, tendency of disease development, degree of dangerousness and hazard extent are analyzed and studied. After a comprehensive analysis of the causes of deformation, the corresponding control measures are presented and are proved to be effective.
Abstract：
The development and engineering characteristics of anti-slide and support structures are introduced, and the conception of buried anti-slide pile with multi-anchor is put forward. The buried anti-slide pile with multi-anchor has been successful applied in landslide controlling project of Jietai Temple in Beijing, indicating that it is very suitable to landslide controlling projects with multi-slide surfaces, heavy layers and high trust. The calculation method and construction technology of the buried anti-slide pile with multi-anchor are preliminarily explored. Taking the landslide controlling project of Jietai Temple as an example, the buried anti-slide pile with multi-anchor is technically and economically compared with the common anti-slide pile. Theresults show that the buried anti-slide pile with multi-anchor has advantages of reducing internal force of piles, balanced force and less displacement. It can save the engineering cost and has broad prospects.
The development and engineering characteristics of anti-slide and support structures are introduced, and the conception of buried anti-slide pile with multi-anchor is put forward. The buried anti-slide pile with multi-anchor has been successful applied in landslide controlling project of Jietai Temple in Beijing, indicating that it is very suitable to landslide controlling projects with multi-slide surfaces, heavy layers and high trust. The calculation method and construction technology of the buried anti-slide pile with multi-anchor are preliminarily explored. Taking the landslide controlling project of Jietai Temple as an example, the buried anti-slide pile with multi-anchor is technically and economically compared with the common anti-slide pile. Theresults show that the buried anti-slide pile with multi-anchor has advantages of reducing internal force of piles, balanced force and less displacement. It can save the engineering cost and has broad prospects.
Abstract：
Based on the project cases in Karst region of Tangshan in recent years, some issues occurred in karst treatment and pile foundation construction are analyzed according to the differences with litho logy, karst developing characteristic and karst treatment method. The methods of karst treatment together with the construction technology of pile foundation are sumarized combining with the technical measures and the application of pile foundation adopted in karst treatment. Meanwhile, comprehensive analysis of the measured values of end bearing, skin friction, pile body stress, pile body compression and pile top settlement is conducted according to the core recovery and RQD of the pile tip resistant layer. The results are regarded as the basis of treatment method and design in similar projects. Aiming at karst developing characteristics and common issues in pile construction, effective construction method, technology and measures are proposed, and it may helpful for the pile foundation construction in similar projects.
Based on the project cases in Karst region of Tangshan in recent years, some issues occurred in karst treatment and pile foundation construction are analyzed according to the differences with litho logy, karst developing characteristic and karst treatment method. The methods of karst treatment together with the construction technology of pile foundation are sumarized combining with the technical measures and the application of pile foundation adopted in karst treatment. Meanwhile, comprehensive analysis of the measured values of end bearing, skin friction, pile body stress, pile body compression and pile top settlement is conducted according to the core recovery and RQD of the pile tip resistant layer. The results are regarded as the basis of treatment method and design in similar projects. Aiming at karst developing characteristics and common issues in pile construction, effective construction method, technology and measures are proposed, and it may helpful for the pile foundation construction in similar projects.
Abstract：
The liquefaction-induced damage of Banqiao School building following the 2008 Wenchuan Ms 8.0 Earthquake is typical, and the correlation between the ground fissures and the liquefaction is identified and mechanisms of the building damages as well as the characters of liquefied soils are investigated by field investigation and in-situ tests, such as multi-channels electric resistance test, spectral analysis of surface wave (SASW), dynamic penetration tests (DPT), borehole and trench, etc. The results show that: (1) the ground fissures are generated by the liquefaction rather than the secondary faults and ruptures; (2) Banqiao School building suffered more severe damages than its surrounding buildings from the liquefaction rather than inertia force of shaking during the Earthquake; (3) the subsurface liquefied soils are gravelly soils at the depth of 3.0-6.1m, which is different from the spouted fine sands; (4) the current knowledge is not true that the gravels are regarded as non-liquefiable soils, and a new procedure for liquefaction evaluation of gravelly soils is demanded.
The liquefaction-induced damage of Banqiao School building following the 2008 Wenchuan Ms 8.0 Earthquake is typical, and the correlation between the ground fissures and the liquefaction is identified and mechanisms of the building damages as well as the characters of liquefied soils are investigated by field investigation and in-situ tests, such as multi-channels electric resistance test, spectral analysis of surface wave (SASW), dynamic penetration tests (DPT), borehole and trench, etc. The results show that: (1) the ground fissures are generated by the liquefaction rather than the secondary faults and ruptures; (2) Banqiao School building suffered more severe damages than its surrounding buildings from the liquefaction rather than inertia force of shaking during the Earthquake; (3) the subsurface liquefied soils are gravelly soils at the depth of 3.0-6.1m, which is different from the spouted fine sands; (4) the current knowledge is not true that the gravels are regarded as non-liquefiable soils, and a new procedure for liquefaction evaluation of gravelly soils is demanded.
Abstract：
Accurate assessment of dynamic compaction reinforcement effect for crushed rock soil fill foundation in moun- tainous areas is a common concern problem. The reinforcing mechanism of dynamic compaction for crushed rock soil fill foundation is analyzed. Then, based on the characteristics of crushed rock soil fill foundation in mountain areas, the validity and rationality of formula estimating method and test method to evaluate dynamic compaction reinforcement effect are studied. At the same time, an actual project is analyzed for further discussion. The results indicate that using the formula estimating method to evaluate the dynamic compaction reinforcement effect for crushed rock soil fill foundation in mountainous areas has limitations. While a single test evaluation method has high cost and low reliability. Only to evaluate the reinforcement effect by applying the Rayleigh waves, static load tests and dynamic penetration tests comprehensively is a reliable and economy method, and the comprehensive evaluation by using the bearing capacity of foundation and deformation modulus is a reasonable and applicable judging criterion for the effective improvement depth.
Accurate assessment of dynamic compaction reinforcement effect for crushed rock soil fill foundation in moun- tainous areas is a common concern problem. The reinforcing mechanism of dynamic compaction for crushed rock soil fill foundation is analyzed. Then, based on the characteristics of crushed rock soil fill foundation in mountain areas, the validity and rationality of formula estimating method and test method to evaluate dynamic compaction reinforcement effect are studied. At the same time, an actual project is analyzed for further discussion. The results indicate that using the formula estimating method to evaluate the dynamic compaction reinforcement effect for crushed rock soil fill foundation in mountainous areas has limitations. While a single test evaluation method has high cost and low reliability. Only to evaluate the reinforcement effect by applying the Rayleigh waves, static load tests and dynamic penetration tests comprehensively is a reliable and economy method, and the comprehensive evaluation by using the bearing capacity of foundation and deformation modulus is a reasonable and applicable judging criterion for the effective improvement depth.
Abstract：
The e xpanding velocity and expansion ratio of the original expansive soils are studied by means of the indoor free expansion ratio tests and linear swelling ratio tests. According to the vertical load, the expansion processes of the expansive soils in one-way immersion under different vertical load s are divided into three types, namely no load acting, small load acting and big load acting, and are separately divided into different parts. The trends of expansion ratio, dry density post expansion, void ratio post expansion, moisture content post expansion under different loads are investigated. It is shown that along with the increase of loads the expansion ratio under loads, void ratio post expansion and moisture content post expansion decrease, and the dry density post expansion increases. The ultimate vertical expansion ratio has a positive semi-logarithmic linear correlation with the water absorption rate . According to the allowable deformation of the soils of the project, the allowable expansibility is determined. Then the retaining wall is designed.
The e xpanding velocity and expansion ratio of the original expansive soils are studied by means of the indoor free expansion ratio tests and linear swelling ratio tests. According to the vertical load, the expansion processes of the expansive soils in one-way immersion under different vertical load s are divided into three types, namely no load acting, small load acting and big load acting, and are separately divided into different parts. The trends of expansion ratio, dry density post expansion, void ratio post expansion, moisture content post expansion under different loads are investigated. It is shown that along with the increase of loads the expansion ratio under loads, void ratio post expansion and moisture content post expansion decrease, and the dry density post expansion increases. The ultimate vertical expansion ratio has a positive semi-logarithmic linear correlation with the water absorption rate . According to the allowable deformation of the soils of the project, the allowable expansibility is determined. Then the retaining wall is designed.
Abstract：
The jet grouting mixing stiffening pile is a new and initiative supporting technology in foundation pits. Engineering practices show that the unique structural design of stiffening piles enhances the pullout resistance and soil strength. The foundation deformation of stiffening piles is better than that of bolting and nailing in soft soil. The load-deformation laws of stiffening pile are illustrated by static load tests. A method to quantitatively assess the pile side soil reinforcement of stiffening piles is derived. It is proposed that the rheological stress and concentration stress are the key factors to apply the stiffening piles in soft foundation pits. The reinforcement and support stiffness method is put for ward to guide the design and construction.
The jet grouting mixing stiffening pile is a new and initiative supporting technology in foundation pits. Engineering practices show that the unique structural design of stiffening piles enhances the pullout resistance and soil strength. The foundation deformation of stiffening piles is better than that of bolting and nailing in soft soil. The load-deformation laws of stiffening pile are illustrated by static load tests. A method to quantitatively assess the pile side soil reinforcement of stiffening piles is derived. It is proposed that the rheological stress and concentration stress are the key factors to apply the stiffening piles in soft foundation pits. The reinforcement and support stiffness method is put for ward to guide the design and construction.
Abstract：
According to the complexity and changeability of the tunnels construction in karst aeras, geological disasters such as water flush and mud rush often occur during construction of tunnels ， which bring much economic loss to construction ， mostly also bring surface water to exhaustion and pollute environment ， etc. At present ， the effective measure to prevent disaster occurrence is improving the accuracy of the geological prediction in karst tunnels and taking the corresponding preventive measures promptly. First, the primary content of geological prediction is summarized. Then, as for the water flush in the process of excavating Qipanshi #3 cross tunnel ， the characteristics and types of caves in front of the face are analyzed based on the geological investigation, the location and size of the caves in front of the face are speculated by TSP-203, GPR and horizontal geological drilling machine, and the caves in front of the face are excavated based on the results of geological prediction. The actual situation after excavation and the geological prediction results are compared, the consistent parts of them are summarized ， the reasons of the inconsistent parts are analyzed, and the existing problems are discussed. The purpose of the research is to improve the accuracy of the geological prediction and to reduce the investment and casualties of the project to the best extent in construction of karst tunnels.
According to the complexity and changeability of the tunnels construction in karst aeras, geological disasters such as water flush and mud rush often occur during construction of tunnels ， which bring much economic loss to construction ， mostly also bring surface water to exhaustion and pollute environment ， etc. At present ， the effective measure to prevent disaster occurrence is improving the accuracy of the geological prediction in karst tunnels and taking the corresponding preventive measures promptly. First, the primary content of geological prediction is summarized. Then, as for the water flush in the process of excavating Qipanshi #3 cross tunnel ， the characteristics and types of caves in front of the face are analyzed based on the geological investigation, the location and size of the caves in front of the face are speculated by TSP-203, GPR and horizontal geological drilling machine, and the caves in front of the face are excavated based on the results of geological prediction. The actual situation after excavation and the geological prediction results are compared, the consistent parts of them are summarized ， the reasons of the inconsistent parts are analyzed, and the existing problems are discussed. The purpose of the research is to improve the accuracy of the geological prediction and to reduce the investment and casualties of the project to the best extent in construction of karst tunnels.
Abstract：
Wenchuan Earthquake causes a large number of geo-hazards in Wudu District and Wenxian County of Gansu Province. After a field investigation and the interpretation of remote-sensing images taken after the earthquake ， 993 earthquake-induced geo-hazards are obtained. Then, the distribution of these geo-hazards is investigated statistically using GIS techniques to determine how the occurrence of geo-hazards correlates with distance from the rivers, slopes, elevations and aspect s. The main results of this research can be summarized as follows: (1) the geo-hazards triggered by earthquake show the feature of zonal distribution along the rivers; (2) the geo-hazards density increases with the increase of earth intensity; (3) the earthquake-induced geo-hazards have corresponding relationship with the elevation, and for most hazards occur below the elevation of 1000 to 2000 m; (4) the slope steepness is a main factor which controls the development of earthquake-induced geo-hazards and a vast majority of geo-hazards are distributed within the range of 10 ° to 40 ° ; (5) aspect influences on the geo-hazards triggered by the Earthquake, and more hazards occur in aspect of due south and southeast.
Wenchuan Earthquake causes a large number of geo-hazards in Wudu District and Wenxian County of Gansu Province. After a field investigation and the interpretation of remote-sensing images taken after the earthquake ， 993 earthquake-induced geo-hazards are obtained. Then, the distribution of these geo-hazards is investigated statistically using GIS techniques to determine how the occurrence of geo-hazards correlates with distance from the rivers, slopes, elevations and aspect s. The main results of this research can be summarized as follows: (1) the geo-hazards triggered by earthquake show the feature of zonal distribution along the rivers; (2) the geo-hazards density increases with the increase of earth intensity; (3) the earthquake-induced geo-hazards have corresponding relationship with the elevation, and for most hazards occur below the elevation of 1000 to 2000 m; (4) the slope steepness is a main factor which controls the development of earthquake-induced geo-hazards and a vast majority of geo-hazards are distributed within the range of 10 ° to 40 ° ; (5) aspect influences on the geo-hazards triggered by the Earthquake, and more hazards occur in aspect of due south and southeast.
Abstract：
The distribution of landslide K7 — K45 section of Shizhu-Zhongxian Highway is analyzed. The distribution laws of landslide are influenced by topography, character of strata and geologic formation. So the design of highways is to avoid disease. If the highway can’t avoid the disease, the designer must give suggestions for proper measures. The main causes for landslide are investigated. To change the inner factor is difficult, so proper measures are necessary. Building highways will cause disease of old landslide and produce disease of new landslide. The treatment of landslide must be considered in the construction of highways. The principle of treating the disease as early as possible and avoiding treating the disease again and again should be aclopted.
The distribution of landslide K7 — K45 section of Shizhu-Zhongxian Highway is analyzed. The distribution laws of landslide are influenced by topography, character of strata and geologic formation. So the design of highways is to avoid disease. If the highway can’t avoid the disease, the designer must give suggestions for proper measures. The main causes for landslide are investigated. To change the inner factor is difficult, so proper measures are necessary. Building highways will cause disease of old landslide and produce disease of new landslide. The treatment of landslide must be considered in the construction of highways. The principle of treating the disease as early as possible and avoiding treating the disease again and again should be aclopted.
Abstract：
It is often necessary to implement geosynthetics to reduce risk of sinkhole for roadbed engineering in karst areas, while the theory for design and analysis is far behind the engineering practices. Firstly, the load on the reinforcement is analyzed, and the Terzaghi's arch theory is introduced to calculate the load above sinkhole. The reinforcement is considered composing of three portions which are portion above sinkhole, changeover portion and anchored portion adjacent to sinikhole according to various loading transfer behaviors. The relationship between tension and displacement at the edge of cavity is deduced for the portion above sinkhole. The tension loss is obtained by introducing the Coulumb's law for the changeover portion. The anchored portion is divided into elastic and plastic sections to be solved, and the analytical solution and length of plastic section are deduced by taking the anchored portion as finite or infinite length. Then, a method is proposed to solve the problem by cross of curves. The proposed method is applied in analyzing pull-out tests and full-scale tests. The results shows that the calculated results agree with the measured ones.
It is often necessary to implement geosynthetics to reduce risk of sinkhole for roadbed engineering in karst areas, while the theory for design and analysis is far behind the engineering practices. Firstly, the load on the reinforcement is analyzed, and the Terzaghi's arch theory is introduced to calculate the load above sinkhole. The reinforcement is considered composing of three portions which are portion above sinkhole, changeover portion and anchored portion adjacent to sinikhole according to various loading transfer behaviors. The relationship between tension and displacement at the edge of cavity is deduced for the portion above sinkhole. The tension loss is obtained by introducing the Coulumb's law for the changeover portion. The anchored portion is divided into elastic and plastic sections to be solved, and the analytical solution and length of plastic section are deduced by taking the anchored portion as finite or infinite length. Then, a method is proposed to solve the problem by cross of curves. The proposed method is applied in analyzing pull-out tests and full-scale tests. The results shows that the calculated results agree with the measured ones.
Abstract：
In order to reduce negative skin friction and improve positive skin friction of piles which is are embedded in soft ground, a new pile type, cast-in-place belled wedge reinforced concrete pile (referred to as belled wedge pile), is developed. The design method and construction process of the belled wedge pile are introduced. Based on FLAC3D, the accuracy is verified by analyzing model test examples, and the properties of negative skin friction of balled wedge pile groups are preliminarily studied. The parametric studies on pile spacing, taper angles, pile-soil modulus ratio and coefficient, and soil layered modulus ratio are carried out and discussed. The conventional equal section pile which is in the same concrete volume is comparatively analyzed. It is shown that 16 % - 20 % of downdrag can be reduced by small taper angles (between 0.4o – 1.0o) compareed with the equal section pile, which shows that taper angle can reduce downdrag effectively.
In order to reduce negative skin friction and improve positive skin friction of piles which is are embedded in soft ground, a new pile type, cast-in-place belled wedge reinforced concrete pile (referred to as belled wedge pile), is developed. The design method and construction process of the belled wedge pile are introduced. Based on FLAC3D, the accuracy is verified by analyzing model test examples, and the properties of negative skin friction of balled wedge pile groups are preliminarily studied. The parametric studies on pile spacing, taper angles, pile-soil modulus ratio and coefficient, and soil layered modulus ratio are carried out and discussed. The conventional equal section pile which is in the same concrete volume is comparatively analyzed. It is shown that 16 % - 20 % of downdrag can be reduced by small taper angles (between 0.4o – 1.0o) compareed with the equal section pile, which shows that taper angle can reduce downdrag effectively.
Abstract：
Manganese is a trace heavy metal. Toxic effect will be caused by excessive intake of manganese. The control of manganese discharge into environment has been attracted much attention recently. Loess soil is used to study the behaviors of removing Mn(II) from aqueous solutions due to its low cost and easy availability. Factors including reaction time, concentration of Mn(II), temperature and complexing agent nitriletriacetic acid (NTA) are studied. The adsorption of Mn(II) on loess soil is a fast process and can reach equilibrium within 1 h. The kinetic data fit the pseudo-second order kinetics model very well, and the reaction rate decreases with the increasing initial concentration of Mn(II). The adsorption capacity of Mn(II) on loess soil is determined to be 7.829 mg/g, and high temperature favors the adsorption process. NTA has contribution on the desorption of Mn(II) from loess soil. The higher concentration of NTA, the more Mn(II) is desorbed. When the amount of Mn(II) laden in loess soil is small, nearly all Mn(II) can be desorbed from loess soil. Clay minerals and organic matter in loess play important roles in Mn(II) adsorption, and ion exchange is the main adsorption mechanism. The results provide an evidence for loess soil as containment barrier system and as adsorbent removing heavy metal contamination in aquatic environment. The introducing of NTA has a certain reference value for remediation of contaminated soil.
Manganese is a trace heavy metal. Toxic effect will be caused by excessive intake of manganese. The control of manganese discharge into environment has been attracted much attention recently. Loess soil is used to study the behaviors of removing Mn(II) from aqueous solutions due to its low cost and easy availability. Factors including reaction time, concentration of Mn(II), temperature and complexing agent nitriletriacetic acid (NTA) are studied. The adsorption of Mn(II) on loess soil is a fast process and can reach equilibrium within 1 h. The kinetic data fit the pseudo-second order kinetics model very well, and the reaction rate decreases with the increasing initial concentration of Mn(II). The adsorption capacity of Mn(II) on loess soil is determined to be 7.829 mg/g, and high temperature favors the adsorption process. NTA has contribution on the desorption of Mn(II) from loess soil. The higher concentration of NTA, the more Mn(II) is desorbed. When the amount of Mn(II) laden in loess soil is small, nearly all Mn(II) can be desorbed from loess soil. Clay minerals and organic matter in loess play important roles in Mn(II) adsorption, and ion exchange is the main adsorption mechanism. The results provide an evidence for loess soil as containment barrier system and as adsorbent removing heavy metal contamination in aquatic environment. The introducing of NTA has a certain reference value for remediation of contaminated soil.
Abstract：
The main characteristics of soft soil in Pearl River Delta are introduced. Based on design of treatment of a soft soil foundation in Zhuhai, the calculation of consolidation degree , check computations of loading stability and soil strength increment are depicted. The method for computing average consolidation degree in the relevant criterion is revised, and the results of settlement are improved. According to the observations and tests after the completion of construction, the revised results are validated. Finally, the observations indicate that the design is successful and it can be a valuable reference for the similar projects.
The main characteristics of soft soil in Pearl River Delta are introduced. Based on design of treatment of a soft soil foundation in Zhuhai, the calculation of consolidation degree , check computations of loading stability and soil strength increment are depicted. The method for computing average consolidation degree in the relevant criterion is revised, and the results of settlement are improved. According to the observations and tests after the completion of construction, the revised results are validated. Finally, the observations indicate that the design is successful and it can be a valuable reference for the similar projects.
Abstract：
The slope failure is a kind of frequently-encountered geotechnical disaster. Many cases of slope failure are induced by the rapid transition between the saturated state and the unsaturated state of soil due to the heavy rainfall or sudden water drawdown. The slope failure induced by these changes can be adequately interpreted by the shear strength theory of unsaturated soil. Three distinct stages are systematically introduced to clearly illustrate the staged development of finite element methods for stability of unsaturated soil slopes, that is, time-independent qualitative analysis, time-dependent analysis with decoupled pore fluid flow and deformation, and fully coupled solid-fluid analysis.
The slope failure is a kind of frequently-encountered geotechnical disaster. Many cases of slope failure are induced by the rapid transition between the saturated state and the unsaturated state of soil due to the heavy rainfall or sudden water drawdown. The slope failure induced by these changes can be adequately interpreted by the shear strength theory of unsaturated soil. Three distinct stages are systematically introduced to clearly illustrate the staged development of finite element methods for stability of unsaturated soil slopes, that is, time-independent qualitative analysis, time-dependent analysis with decoupled pore fluid flow and deformation, and fully coupled solid-fluid analysis.
Abstract：
A highway slope anchor is taken as an example. The methods failure criteria and procedures of the existing anchoring construction anchors are intredused. The experimental process and the acquired experimental data in the practical project are offered. The achieved experimental data and several cases of a serving anchoring project anchor stretch-draw damage are analyzed and calculated. It illustrates how to use field drawing experimental results to determine the design parameters of the relevant strata prestressed anchors. The ultimate pullout capacity of different prestressed anchors are compared. The pratical free end elongation and theoretical elongation of anchors are compared and analyzed. The factors which affects tension deformation and damage of prestressed anchors are discussed combining with the test process of a practical project. Finally, some conclusions are drawn.
A highway slope anchor is taken as an example. The methods failure criteria and procedures of the existing anchoring construction anchors are intredused. The experimental process and the acquired experimental data in the practical project are offered. The achieved experimental data and several cases of a serving anchoring project anchor stretch-draw damage are analyzed and calculated. It illustrates how to use field drawing experimental results to determine the design parameters of the relevant strata prestressed anchors. The ultimate pullout capacity of different prestressed anchors are compared. The pratical free end elongation and theoretical elongation of anchors are compared and analyzed. The factors which affects tension deformation and damage of prestressed anchors are discussed combining with the test process of a practical project. Finally, some conclusions are drawn.
Abstract：
With the speedy development of metro construction in China, more and more attention has been paid to shield directly crossing underground ventilation adit of metro station. By taking Gaojiayuan Station of the experimental project of Beijing Metro Line No. 14 as an engineering background, a large-size earth pressure balanced (EPB) shield with an outer diameter of 10 m directly crossing an underground ventilation adit is simulated by means of three-dimensional finite element method based on the soil-structure interaction theory. The total displacement and stress of the ventilation adit is obtained, and the influence of the large-diameter EPB shield tunneling on the deformation and stress characteristics of the ventilation adit is analyzed. The numerical results show that the deformation of the ventilation adit mainly focuses on the ring beams, and the maximum deformation occurs at the top of the ring beams. Moreover, the deformations of the left and right ring beams increase dramatically before and after shield crossing the ventilation adit. The maximum stress of the ventilation adit also appears on the ring beams, and the stresses on the left and right ring beams vary largely during the shield crossing the ventilation adit. With the increase of the supporting pressure on the excavation face, the left ring beam is subjected to greater deformation and stress during the construction, compared with other structures. It is therefore suggested that the ring beams of the ventilation adit should be reinforced in the design and the supporting pressure on the excavation face should be adjusted at an appropriate level to ensure the safety of the ventilation adit.
With the speedy development of metro construction in China, more and more attention has been paid to shield directly crossing underground ventilation adit of metro station. By taking Gaojiayuan Station of the experimental project of Beijing Metro Line No. 14 as an engineering background, a large-size earth pressure balanced (EPB) shield with an outer diameter of 10 m directly crossing an underground ventilation adit is simulated by means of three-dimensional finite element method based on the soil-structure interaction theory. The total displacement and stress of the ventilation adit is obtained, and the influence of the large-diameter EPB shield tunneling on the deformation and stress characteristics of the ventilation adit is analyzed. The numerical results show that the deformation of the ventilation adit mainly focuses on the ring beams, and the maximum deformation occurs at the top of the ring beams. Moreover, the deformations of the left and right ring beams increase dramatically before and after shield crossing the ventilation adit. The maximum stress of the ventilation adit also appears on the ring beams, and the stresses on the left and right ring beams vary largely during the shield crossing the ventilation adit. With the increase of the supporting pressure on the excavation face, the left ring beam is subjected to greater deformation and stress during the construction, compared with other structures. It is therefore suggested that the ring beams of the ventilation adit should be reinforced in the design and the supporting pressure on the excavation face should be adjusted at an appropriate level to ensure the safety of the ventilation adit.
Abstract：
The ultimate bearing capacity of statically pressed pipe piles is affected by the geometry of piles, property of soil surrounding the piles, pile construction and so on. The grey correlation method is used to analyze the investigation data, construction records and field loading test data of statically pressed pipe piles in Liaoshen area, and the factor sorting which affects the bearing capacity of single pile is acquired. The results show that the ultimate bearing capacity of single pile is end resistance, which is different from that in south area of China. It is advisable to analyze the factors which affect the bearing capacity of statically pressed pipe piles by use of the grey correlation method. The results agree well with the real situation of load distribution. The grey correlation method provides a new research approach for analyzing the bearing mechanism of statically pressed pipe piles and gives some references for researches on relative problems in future.
The ultimate bearing capacity of statically pressed pipe piles is affected by the geometry of piles, property of soil surrounding the piles, pile construction and so on. The grey correlation method is used to analyze the investigation data, construction records and field loading test data of statically pressed pipe piles in Liaoshen area, and the factor sorting which affects the bearing capacity of single pile is acquired. The results show that the ultimate bearing capacity of single pile is end resistance, which is different from that in south area of China. It is advisable to analyze the factors which affect the bearing capacity of statically pressed pipe piles by use of the grey correlation method. The results agree well with the real situation of load distribution. The grey correlation method provides a new research approach for analyzing the bearing mechanism of statically pressed pipe piles and gives some references for researches on relative problems in future.
2011, 33(zk1): 399-402.
Abstract：
The consolidation time in the centrifugal model tests is 1/<>n2 of that in the prototype, thus the long-term settlement of deep soft clay ground can be simulated within short time. Based on the principles of centrifugal model tests, different test schemes are designed and centrifugal model tests are employed to study the improvement mechanism of D-M method. The tests results show that the D-M method is feasible to improve deep soft clay ground. Compared with the deep mixing, the D-M method is beneficial to reduce the differential settlement and the cost of ground treatment. At the same time, the method has better treatment effect than PVD in post-construction settlement and differential settlement.
The consolidation time in the centrifugal model tests is 1/<>n2 of that in the prototype, thus the long-term settlement of deep soft clay ground can be simulated within short time. Based on the principles of centrifugal model tests, different test schemes are designed and centrifugal model tests are employed to study the improvement mechanism of D-M method. The tests results show that the D-M method is feasible to improve deep soft clay ground. Compared with the deep mixing, the D-M method is beneficial to reduce the differential settlement and the cost of ground treatment. At the same time, the method has better treatment effect than PVD in post-construction settlement and differential settlement.
Abstract：
The triaxial equipment of GDS is improved based on the digital image processing technique, and the failure process and shear band mode of medium sand under different stress paths are studied. Thirteen monotonic shearing tests are performed, including isotropic stress consolidation and anisotropic stress consolidation. Deformation characters and strain fields of sample surface at different time during triaxial compression progress are recorded, and the failure progress of samples is presented. The results show that, under different stress paths, the failure progress of samples is closely related to the stress path. Different realizing ways of increasing pore pressure and decreasing the total stress for the same stress path may lead to different results. The final failure mode can be divided into three kinds, namely uniform bulging, single shear band and cross shear band. The effective stress ratio regularity shows that the higher stress ratio of consolidation, the lower value of effective stress ratio and the bigger value of reduction after peak value. The failure mode is initially determined before the peak value of effective stress ratio, macro stability is reached after the peak value.
The triaxial equipment of GDS is improved based on the digital image processing technique, and the failure process and shear band mode of medium sand under different stress paths are studied. Thirteen monotonic shearing tests are performed, including isotropic stress consolidation and anisotropic stress consolidation. Deformation characters and strain fields of sample surface at different time during triaxial compression progress are recorded, and the failure progress of samples is presented. The results show that, under different stress paths, the failure progress of samples is closely related to the stress path. Different realizing ways of increasing pore pressure and decreasing the total stress for the same stress path may lead to different results. The final failure mode can be divided into three kinds, namely uniform bulging, single shear band and cross shear band. The effective stress ratio regularity shows that the higher stress ratio of consolidation, the lower value of effective stress ratio and the bigger value of reduction after peak value. The failure mode is initially determined before the peak value of effective stress ratio, macro stability is reached after the peak value.
Abstract：
Rainfall is one of the main factors which trigger landslide of expansive soil. In order to study the landslide mechanism of expansive soil slope, a rainfall simulation used in centrifugal model tests is designed. The landslide process of expansive soil slope under rainfall is simulated by centrifugal model tests. The results indicate that the landslide appears after the first rainfall, and the scale and depth of landslide after the second rainfall increase which reflects the progressive and gradually tractional landslide of expansive soil. Finally, through the summary analysis based on the test results, the landslide mechanism of expansive soil slope under rainfall is obtained. The failure mode of expansive soil slope is proposed, that is, ‘slope slide under expansive effect’.
Rainfall is one of the main factors which trigger landslide of expansive soil. In order to study the landslide mechanism of expansive soil slope, a rainfall simulation used in centrifugal model tests is designed. The landslide process of expansive soil slope under rainfall is simulated by centrifugal model tests. The results indicate that the landslide appears after the first rainfall, and the scale and depth of landslide after the second rainfall increase which reflects the progressive and gradually tractional landslide of expansive soil. Finally, through the summary analysis based on the test results, the landslide mechanism of expansive soil slope under rainfall is obtained. The failure mode of expansive soil slope is proposed, that is, ‘slope slide under expansive effect’.
Abstract：
Considering the influences of three factors: cohesion c, over loading q, and density of the soil , a new universal analytical solution of shallow foundation is presented based on the static equilibrium of rigid-plasticity body with the theoretical solution of shallow square foundation and strip foundation. The variation tendency of curves are similar to that of semi-empiric Vesic, Hansen and Meyerhof solutions, and the curves among Nq, Nc, Nr and internal friction angle of soil and ratio of length and width of rectangle foundation are gained. The results of this solution agree with the semi-empiric Vesic solution.
Considering the influences of three factors: cohesion c, over loading q, and density of the soil , a new universal analytical solution of shallow foundation is presented based on the static equilibrium of rigid-plasticity body with the theoretical solution of shallow square foundation and strip foundation. The variation tendency of curves are similar to that of semi-empiric Vesic, Hansen and Meyerhof solutions, and the curves among Nq, Nc, Nr and internal friction angle of soil and ratio of length and width of rectangle foundation are gained. The results of this solution agree with the semi-empiric Vesic solution.
Abstract：
The mechanical behaviors of polypropylene fiber reinforced red clay are studied by means of different test methods. The compaction test and the permeability test show that the maximum dry unit weight of the fiber reinforced red clay is basically a constant value and the variation range of the optimum moisture content is great with certain fiber content. It has the same magnitude of permeability coefficients as the fiber reinforced red clay and the permeability coefficient is small. The results of direct shear test, unconfined compressive test and triaxial consolidation undrained test show the strength of the fiber reinforced red clay is obvious higher than that of the red clay, which increases with the fiber content and length. After being mixed with fiber, the cohesion of red clay rises a lot and the change of friction angle is small. The stress-strain curve of the fiber reinforced red clay shows typical work hardening character. The sample has the character of bulging breakage.
The mechanical behaviors of polypropylene fiber reinforced red clay are studied by means of different test methods. The compaction test and the permeability test show that the maximum dry unit weight of the fiber reinforced red clay is basically a constant value and the variation range of the optimum moisture content is great with certain fiber content. It has the same magnitude of permeability coefficients as the fiber reinforced red clay and the permeability coefficient is small. The results of direct shear test, unconfined compressive test and triaxial consolidation undrained test show the strength of the fiber reinforced red clay is obvious higher than that of the red clay, which increases with the fiber content and length. After being mixed with fiber, the cohesion of red clay rises a lot and the change of friction angle is small. The stress-strain curve of the fiber reinforced red clay shows typical work hardening character. The sample has the character of bulging breakage.
Abstract：
The shear strength reduction finite element method has become a main technique in the field of slope stability analysis due to its advantages of dealing with complex geometry and nonlinear material, and no need of predefined critical slip surface. Three main problems of shear strength reduction technology including the criteria for failure are discussed. An example analyzed by the ideal elastoplasticity model and rheological model is used to show the advantages and disadvantages of rheological model applied in slope stability calculation. And a user-defined subroutine is developed based on the Duncan-Chang EB model, Mohr-Coulomb model and logarithmical shear strength model, which is used to find the safety factor of Nuozhadu Embankment Dam with a height of 261.5 m.
The shear strength reduction finite element method has become a main technique in the field of slope stability analysis due to its advantages of dealing with complex geometry and nonlinear material, and no need of predefined critical slip surface. Three main problems of shear strength reduction technology including the criteria for failure are discussed. An example analyzed by the ideal elastoplasticity model and rheological model is used to show the advantages and disadvantages of rheological model applied in slope stability calculation. And a user-defined subroutine is developed based on the Duncan-Chang EB model, Mohr-Coulomb model and logarithmical shear strength model, which is used to find the safety factor of Nuozhadu Embankment Dam with a height of 261.5 m.
Abstract：
Taking a complicated foundation pit in Lanzhou as the background, the application of soil nailing walls, composite soil nailing walls and pile-prestressed anchors are respectively introduced, and the key construction technology is discussed. The monitoring results show that, the design scheme for the supporting is reasonable, the effectiveness is good, and the requirements of design and environment are satisfied. The experience of this project is significant to similar projects in Lanzhou.
Taking a complicated foundation pit in Lanzhou as the background, the application of soil nailing walls, composite soil nailing walls and pile-prestressed anchors are respectively introduced, and the key construction technology is discussed. The monitoring results show that, the design scheme for the supporting is reasonable, the effectiveness is good, and the requirements of design and environment are satisfied. The experience of this project is significant to similar projects in Lanzhou.
Abstract：
On the basis of comparison and summarization of theoretical studies on soil anisotropy under the principal stress rotation, a new method for studying the yield suface of a constitutive model under different load directions is proposed. Using this new method, the satisfactory yield function under different load directions can be derived, and taking the Sekiguchi and Ohta model as an example, the yield surfaces under different load directions are plotted in <>p – <> q space. It is valuable to the theoretical researches on anisotropic yield surfaces.
On the basis of comparison and summarization of theoretical studies on soil anisotropy under the principal stress rotation, a new method for studying the yield suface of a constitutive model under different load directions is proposed. Using this new method, the satisfactory yield function under different load directions can be derived, and taking the Sekiguchi and Ohta model as an example, the yield surfaces under different load directions are plotted in <>p – <> q space. It is valuable to the theoretical researches on anisotropic yield surfaces.
Abstract：
The relationships among the initial water content, compactness, cover load and expansion rate are studied through expansion experiments in the state of <>K0 stress for Handan strong expansive soil. The expansion rate under small pressure is declined sharply relative to unloading. The expansion rates under small loading (<6.25 kPa) and large loading are difficult to be described by one equation. The formulae of no-load expansion rate and loaded expansion rate are established respectively based on the compactness and the initial water content. The expansion rate between 0~6.25 kPa can be calculated by linear interpolation according to the no-load expansion rate and that under the pressure of 6.25 kPa. Finally, an expansion model in the state of <>K0 stress is established. This model is available to soil for different expensive classes and of promotional value.
The relationships among the initial water content, compactness, cover load and expansion rate are studied through expansion experiments in the state of <>K0 stress for Handan strong expansive soil. The expansion rate under small pressure is declined sharply relative to unloading. The expansion rates under small loading (<6.25 kPa) and large loading are difficult to be described by one equation. The formulae of no-load expansion rate and loaded expansion rate are established respectively based on the compactness and the initial water content. The expansion rate between 0~6.25 kPa can be calculated by linear interpolation according to the no-load expansion rate and that under the pressure of 6.25 kPa. Finally, an expansion model in the state of <>K0 stress is established. This model is available to soil for different expensive classes and of promotional value.
Abstract：
Two groups of tests of unidirectional rotation of the principal stresses are conducted on dry Fujian standard sand by means of the dynamic hollow cylinder apparatus at Tongji University. The investigation highlights the influences of deviatoric stress ratio and intermediate stress parameter on deformation behaviors and non-coaxiality of dry sands. The mean stress and intermediate stress parameter are maintained as constant with a variation of deviatoric stress ratios in one test group, while the mean stress and deviatoric stress are maintained as constant with a variation of intermediate stress parameters in the other test group. The experimental results show that the deviatoric stress ratio and intermediate stress parameter have significant influences on deformation behaviors of dry sands.
Two groups of tests of unidirectional rotation of the principal stresses are conducted on dry Fujian standard sand by means of the dynamic hollow cylinder apparatus at Tongji University. The investigation highlights the influences of deviatoric stress ratio and intermediate stress parameter on deformation behaviors and non-coaxiality of dry sands. The mean stress and intermediate stress parameter are maintained as constant with a variation of deviatoric stress ratios in one test group, while the mean stress and deviatoric stress are maintained as constant with a variation of intermediate stress parameters in the other test group. The experimental results show that the deviatoric stress ratio and intermediate stress parameter have significant influences on deformation behaviors of dry sands.
2011, 33(zk1): 454-458.
Abstract：
By using the trial stress return mapping algorithm, a user-defined material subroutine (UMAT) of the constitutive model of soil considering complex stress path is complied. The precision of the UMAT is tested by simulating triaxial compression tests and triaxial extension tests based on ABAQUS. Three-dimensional finite element analysis of excavating small diameter axisymmetric round foundation is carried out by means of the second-developed ABAQUS with the UMAT. The variations of the intermediate principal stress and the minimum principal stress and the laws of soil arch caused by the intermediate principal stress under the plane strain condition are studied.
By using the trial stress return mapping algorithm, a user-defined material subroutine (UMAT) of the constitutive model of soil considering complex stress path is complied. The precision of the UMAT is tested by simulating triaxial compression tests and triaxial extension tests based on ABAQUS. Three-dimensional finite element analysis of excavating small diameter axisymmetric round foundation is carried out by means of the second-developed ABAQUS with the UMAT. The variations of the intermediate principal stress and the minimum principal stress and the laws of soil arch caused by the intermediate principal stress under the plane strain condition are studied.
Abstract：
Influenced by the regional climate and external environment conditions, the typical embankments in permafrost regions along the Qinghai-Tibet Railway have specific characteristics in terms of thermal stability and engineering stability. In consideration of the climate and environment conditions in permafrost regions, the embankment sections of the Qinghai-Tibet Railway from Golmud to northern Lhasa are selected as experimental samples. The stress-strain field and deformation of embankments under the action of temperature field coupled with the dynamic field generated by train load in permafrost regions along the Qinghai-Tibet Railway are simulated. Finally, the engineering measures to control the deformation of the embankments in permafrost regions are evaluated.
Influenced by the regional climate and external environment conditions, the typical embankments in permafrost regions along the Qinghai-Tibet Railway have specific characteristics in terms of thermal stability and engineering stability. In consideration of the climate and environment conditions in permafrost regions, the embankment sections of the Qinghai-Tibet Railway from Golmud to northern Lhasa are selected as experimental samples. The stress-strain field and deformation of embankments under the action of temperature field coupled with the dynamic field generated by train load in permafrost regions along the Qinghai-Tibet Railway are simulated. Finally, the engineering measures to control the deformation of the embankments in permafrost regions are evaluated.
Abstract：
Tunnelling in weak and fractured rock mass will inevitably induce excessive stress or deformation of surrounding rock, which results in tunnel face collapse accidents. In order to understand the failure modes and progressive failure characteristics, the weak and fractured rock mass of grade Ⅳ according to Chinese codes is taken as the reference prototype. This rock mass is firstly equivalent for isotropic continual stratum, and then modeled by similar materials. Subsequently, model tests are carried out to simulate tunnel excavation under different loading modes. The test results show that, the tunnel face collapses in dome-style in the slow loading mode, while in the fast loading mode, it collapses in chimney shape and reaches ground surface. In the initial stage after excavation, the lateral displacement at the upside of tunnel face is relatively large; with the increase of overlying loads, the lateral displacement at the downside of tunnel face grows drastically and forms the final failure face from bottom to top. After tunnel excavation, the position of the maximal horizontal stress increment locats at the upside of tunnel face near the line center, but the location of maximal vertical stress increment lies in the top of tunnel face profile.
Tunnelling in weak and fractured rock mass will inevitably induce excessive stress or deformation of surrounding rock, which results in tunnel face collapse accidents. In order to understand the failure modes and progressive failure characteristics, the weak and fractured rock mass of grade Ⅳ according to Chinese codes is taken as the reference prototype. This rock mass is firstly equivalent for isotropic continual stratum, and then modeled by similar materials. Subsequently, model tests are carried out to simulate tunnel excavation under different loading modes. The test results show that, the tunnel face collapses in dome-style in the slow loading mode, while in the fast loading mode, it collapses in chimney shape and reaches ground surface. In the initial stage after excavation, the lateral displacement at the upside of tunnel face is relatively large; with the increase of overlying loads, the lateral displacement at the downside of tunnel face grows drastically and forms the final failure face from bottom to top. After tunnel excavation, the position of the maximal horizontal stress increment locats at the upside of tunnel face near the line center, but the location of maximal vertical stress increment lies in the top of tunnel face profile.
Abstract：
The PHC pile foundations with high rafts, part of piles exposing in the air due to the lack of backfill soil, are firstly adopted in the construction of coastal ports in Tianjin. Thus, to evaluate the deformation characteristics of these pipe piles becomes a challenge in engineering practice. A series of field tests are conducted to investigate the soil squeezing effect resulting from pipe piles supporting high rafts in soft soils. The excess pore water pressure and the lateral displacements of soils are monitored and analyzed. The behaviors of dissipation of the excess pore water pressure and the lateral displacement of soils are obtained. The application characteristics of PHC pipe pile foundations with high rafts is presented based on the results. It provides a reference for the application of similar PHC pipe pile foundations with high rafts.
The PHC pile foundations with high rafts, part of piles exposing in the air due to the lack of backfill soil, are firstly adopted in the construction of coastal ports in Tianjin. Thus, to evaluate the deformation characteristics of these pipe piles becomes a challenge in engineering practice. A series of field tests are conducted to investigate the soil squeezing effect resulting from pipe piles supporting high rafts in soft soils. The excess pore water pressure and the lateral displacements of soils are monitored and analyzed. The behaviors of dissipation of the excess pore water pressure and the lateral displacement of soils are obtained. The application characteristics of PHC pipe pile foundations with high rafts is presented based on the results. It provides a reference for the application of similar PHC pipe pile foundations with high rafts.
Abstract：
Under a constant load, considering the influences of smear zone and nonlinear characteristics of soil, assuming that there is only radial flow in weak drainage piles, a governing equation under the assumption of equal strain is derived. The validity of the proposed method is conformed through being equivalent to Terzaghi’s one-dimensional consolidation theory . The analytic results show that: the nonlinear characteristics of soil have great i nfluences on the rate of consolidation , the consolidation velocity of composite ground decreases with the increase of C c / Ck and H / rc , the stress ratio σ0/ σsi has less influences on the rate of consolidation in comparison with Cc/ Ck, the larger the ratio of pile-soil modulus, the faster the consolidation velocity and the less influences of C c / Ck on consolidation, and the consolidation velocity of composite ground with weak drainage pile is mainly under the influences of anisotropy of permeability of soil.
Under a constant load, considering the influences of smear zone and nonlinear characteristics of soil, assuming that there is only radial flow in weak drainage piles, a governing equation under the assumption of equal strain is derived. The validity of the proposed method is conformed through being equivalent to Terzaghi’s one-dimensional consolidation theory . The analytic results show that: the nonlinear characteristics of soil have great i nfluences on the rate of consolidation , the consolidation velocity of composite ground decreases with the increase of C c / Ck and H / rc , the stress ratio σ0/ σsi has less influences on the rate of consolidation in comparison with Cc/ Ck, the larger the ratio of pile-soil modulus, the faster the consolidation velocity and the less influences of C c / Ck on consolidation, and the consolidation velocity of composite ground with weak drainage pile is mainly under the influences of anisotropy of permeability of soil.
Abstract：
Natural liquefiable sandy ground and liquefiable sandy ground improved by gravel piles and soil cement piles under earthquake action are numerically simulated by three-dimensional finite difference program “FLAC3D” (Fast Lagrangian analysis of continua), and anti-liquefaction characteristics of gravel piles and soil-cement piles in improving the liquefiable sandy ground are studied. The analysis shows that the gravel piles have remarkable effect to resist liquefaction, while the cement-soil piles have limit effect to resist liquefaction. It is also confirmed that the resisting liquefaction effects and the drainage effects of pile-soil are directly correlative .
Natural liquefiable sandy ground and liquefiable sandy ground improved by gravel piles and soil cement piles under earthquake action are numerically simulated by three-dimensional finite difference program “FLAC3D” (Fast Lagrangian analysis of continua), and anti-liquefaction characteristics of gravel piles and soil-cement piles in improving the liquefiable sandy ground are studied. The analysis shows that the gravel piles have remarkable effect to resist liquefaction, while the cement-soil piles have limit effect to resist liquefaction. It is also confirmed that the resisting liquefaction effects and the drainage effects of pile-soil are directly correlative .
Abstract：
A numerical model of 3D FEM for suction tapered bucket foundations is established based on the Mohr-Coulomb constitutive criterion, and is also verified by model tests. On this basis, the analysis and computation are carried out, and the dependency relationship between the factors of aspect ratio and bucket slop and the bearing capacity of tapered bucket foundation in saturated soft clay is studied. Based on the empirical expression by Vesic, a vertical bearing formula for tapered single bucket foundations, with the action that the bucket is cohered with the contacted clay, is presented. A comparison shows that the calculated results of this formula is consistent with those of FEM.
A numerical model of 3D FEM for suction tapered bucket foundations is established based on the Mohr-Coulomb constitutive criterion, and is also verified by model tests. On this basis, the analysis and computation are carried out, and the dependency relationship between the factors of aspect ratio and bucket slop and the bearing capacity of tapered bucket foundation in saturated soft clay is studied. Based on the empirical expression by Vesic, a vertical bearing formula for tapered single bucket foundations, with the action that the bucket is cohered with the contacted clay, is presented. A comparison shows that the calculated results of this formula is consistent with those of FEM.
Abstract：
The analysis and simulation work concerning rainfall infiltration and motion equation of slope runoff are carried out based on achievements of related research subjects based on the theories of infiltration and flow fluctuations. The influence rules of runoff time and production flow are deduced. The influencing factors include rainfall intensity, permeability coefficient , soil suction, compactness , water content, Manning's roughness coefficient, slope gradient and slope length . The results show the rainfall intensity has more impact on the runoff time and production flow. In prolonged rainfall, the slope length affects the cutting slope. In short rains, the larger roughness and slope decrease are the important factors to reduce the runoff.
The analysis and simulation work concerning rainfall infiltration and motion equation of slope runoff are carried out based on achievements of related research subjects based on the theories of infiltration and flow fluctuations. The influence rules of runoff time and production flow are deduced. The influencing factors include rainfall intensity, permeability coefficient , soil suction, compactness , water content, Manning's roughness coefficient, slope gradient and slope length . The results show the rainfall intensity has more impact on the runoff time and production flow. In prolonged rainfall, the slope length affects the cutting slope. In short rains, the larger roughness and slope decrease are the important factors to reduce the runoff.
Abstract：
The load transfer method is one of frequently-used means to study the bearing behaviors of piles. Supposing different parameters of piles and soil as well as loading conditions, a differential equation of piles and soil is established according to the condition of static equilibrium, where an exponential curve model is modified for load transfer function with softening or hardening of soil. The matrix displacement method programmed by MATLAB language is used to solve the differential equation, and it will give the resistances of side, axial forces and vertical displacements in different cross sections of piles. Simulation analysis is taken on the influences by the variation of the properties of soil around piles. The results show that the pile top settlement in topsoil of high strength is lower than that in subsoil of high strength under the same piles and loads, and the load proportions shared by tip will gradually converge to some level with the increase of loads. The top settlement and the tip resistance of pile are not obviously influenced by the degree of the softening or hardening of soil around piles at the beginning stage of loading. However, the higher the load is, the greater the difference between softening and hardening of top settlement and the load proportions shared by tip are. The increment of the general ultimate pile resistance will help improve the bearing capacity of the piles.
The load transfer method is one of frequently-used means to study the bearing behaviors of piles. Supposing different parameters of piles and soil as well as loading conditions, a differential equation of piles and soil is established according to the condition of static equilibrium, where an exponential curve model is modified for load transfer function with softening or hardening of soil. The matrix displacement method programmed by MATLAB language is used to solve the differential equation, and it will give the resistances of side, axial forces and vertical displacements in different cross sections of piles. Simulation analysis is taken on the influences by the variation of the properties of soil around piles. The results show that the pile top settlement in topsoil of high strength is lower than that in subsoil of high strength under the same piles and loads, and the load proportions shared by tip will gradually converge to some level with the increase of loads. The top settlement and the tip resistance of pile are not obviously influenced by the degree of the softening or hardening of soil around piles at the beginning stage of loading. However, the higher the load is, the greater the difference between softening and hardening of top settlement and the load proportions shared by tip are. The increment of the general ultimate pile resistance will help improve the bearing capacity of the piles.
Abstract：
Thermal probes, a device to exchange heat with air and liquor convert, have characteristics of no engine loss and highly decreasing earth temperature around the thermal probes. The thermal probes have obvious effects for decreasing earth temperature under the foundation, increasing cold storage of earth foundation and protecting permafrost. It is a simple and suitable engineering measure for protecting permafrost. Now it has been widely used in Qinghai-Tibet Railway in permafrost area. In view of application of the thermal probes in the civil engineering, many researches in China and foreign countries are carried out. Many key technologies of thermal probes are solved, for example, making crafts, trail of model in low temperature, design and calculation and so on. But there are not any father researches on the relation among diameter of thermal probes, effect of decreasing earth temperature and producing cold quantity. In order to solve this kind of problems, a series of experiments in permafrost region along the Qinghai-Tibet Railway are performed. The test content includes three thermal probes with the same length but different diameters in Anduo experimental section. In given conditions, within certain range of diameter of thermal probes, the results show: (1) its producing cold quantity doesn’t increase with the increase of the diameter; (2) there seems to be the same decreasing earth temperature and producing cold quantity with different diameters; (3) after comprehensive consideration, the optimal diameter of thermal probes is 89 mm.
Thermal probes, a device to exchange heat with air and liquor convert, have characteristics of no engine loss and highly decreasing earth temperature around the thermal probes. The thermal probes have obvious effects for decreasing earth temperature under the foundation, increasing cold storage of earth foundation and protecting permafrost. It is a simple and suitable engineering measure for protecting permafrost. Now it has been widely used in Qinghai-Tibet Railway in permafrost area. In view of application of the thermal probes in the civil engineering, many researches in China and foreign countries are carried out. Many key technologies of thermal probes are solved, for example, making crafts, trail of model in low temperature, design and calculation and so on. But there are not any father researches on the relation among diameter of thermal probes, effect of decreasing earth temperature and producing cold quantity. In order to solve this kind of problems, a series of experiments in permafrost region along the Qinghai-Tibet Railway are performed. The test content includes three thermal probes with the same length but different diameters in Anduo experimental section. In given conditions, within certain range of diameter of thermal probes, the results show: (1) its producing cold quantity doesn’t increase with the increase of the diameter; (2) there seems to be the same decreasing earth temperature and producing cold quantity with different diameters; (3) after comprehensive consideration, the optimal diameter of thermal probes is 89 mm.
Abstract：
A deformation mechanism method is proposed based on the concept “tunnel-slope system”, taking the outlet section of the shallow tunnel under unsymmetrical pressure of Hanjiamo tunnel No. 3 as the study object. The engineering geological conditions are investigated by using this method. The structural type and deformation mechanism of the system are studied considering the deformation characteristics and monitoring achievements during the construction process of the outlet section. FLAC3D is used to simulate the excavation and support processes of the outlet of Hanjiamo tunnel No. 3 under the condition of shallow cover and unsymmetrical pressure. Some conclusions are drawn through analyzing the characters of stress and displacement fields and plastic zone of surrounding rock after excavation. It will be useful for the project construction.
A deformation mechanism method is proposed based on the concept “tunnel-slope system”, taking the outlet section of the shallow tunnel under unsymmetrical pressure of Hanjiamo tunnel No. 3 as the study object. The engineering geological conditions are investigated by using this method. The structural type and deformation mechanism of the system are studied considering the deformation characteristics and monitoring achievements during the construction process of the outlet section. FLAC3D is used to simulate the excavation and support processes of the outlet of Hanjiamo tunnel No. 3 under the condition of shallow cover and unsymmetrical pressure. Some conclusions are drawn through analyzing the characters of stress and displacement fields and plastic zone of surrounding rock after excavation. It will be useful for the project construction.
