2009 Vol. 31 No. 3
Abstract：
The model of wavelet least squares support vector machines(WLSSVM) is optimized by adaptive particle swarm optimization(APSO),and a new model named as wavelet least squares support vector machine based on adaptive particle swarm optimization(APSO-WLSSVM) is put forward.The model combines good time domain,frequency domain resolving ability of wavelet transformation and nonlinear learning ability of SVM.The adaptive particle swarm optimization is used to optimize the parameters of SVM so as to avoid artificial arbitrariness and enhance the forecast accuracy.For comparison,the model of APSO-WLSSVM and the traditional SVM(Gauss kernel function) are used to forecast the same displacement time series.The result shows that the former is better than the latter in forecast accuracy.The model is used to forecast the left back slope and diversion tunnel of Jinping First-stage Hydropower Station.The forecast values are in good agreement with the measured ones,indicating that the APSO-WLSSVM is feasible and precise and can be well applied to the forecast of displacement time series.
The model of wavelet least squares support vector machines(WLSSVM) is optimized by adaptive particle swarm optimization(APSO),and a new model named as wavelet least squares support vector machine based on adaptive particle swarm optimization(APSO-WLSSVM) is put forward.The model combines good time domain,frequency domain resolving ability of wavelet transformation and nonlinear learning ability of SVM.The adaptive particle swarm optimization is used to optimize the parameters of SVM so as to avoid artificial arbitrariness and enhance the forecast accuracy.For comparison,the model of APSO-WLSSVM and the traditional SVM(Gauss kernel function) are used to forecast the same displacement time series.The result shows that the former is better than the latter in forecast accuracy.The model is used to forecast the left back slope and diversion tunnel of Jinping First-stage Hydropower Station.The forecast values are in good agreement with the measured ones,indicating that the APSO-WLSSVM is feasible and precise and can be well applied to the forecast of displacement time series.
2009, 31(3): 319-325.
Abstract：
To simulate the continuous rotation of principal stress axes,a set of stress controlled bi-directional cyclic loading tests were conducted.Tests were performed with two cyclic stress components involving the horizontal shear stress(torsional shear stress) and the vertical shear stress(stress difference between vertical normal stress and horizontal normal stress) to provide an approximate presentation of wave or seismic loading conditions.The stress path shown in the orthogonal coordinates of stress difference and shear stress had an elliptical shape.The ratio of the shear amplitude between the longer axis and shorter axis and the area enclosed by elliptical rotational loading path were controlled in a planned way.Test results showed that the stress-strain behavior was significantly affected by the ratio of amplitude of the two shear stress components.But it was nearly independent on the area enclosed by elliptical rotational loading path.The deformation behaviors were classified as two different types based on the ratio value.
To simulate the continuous rotation of principal stress axes,a set of stress controlled bi-directional cyclic loading tests were conducted.Tests were performed with two cyclic stress components involving the horizontal shear stress(torsional shear stress) and the vertical shear stress(stress difference between vertical normal stress and horizontal normal stress) to provide an approximate presentation of wave or seismic loading conditions.The stress path shown in the orthogonal coordinates of stress difference and shear stress had an elliptical shape.The ratio of the shear amplitude between the longer axis and shorter axis and the area enclosed by elliptical rotational loading path were controlled in a planned way.Test results showed that the stress-strain behavior was significantly affected by the ratio of amplitude of the two shear stress components.But it was nearly independent on the area enclosed by elliptical rotational loading path.The deformation behaviors were classified as two different types based on the ratio value.
2009, 31(3): 326-330.
Abstract：
The climate change is one of the important environmental issues,and water conservancy projects are main measures to cope with the climate change.The climate change will have effect on the design standards,operation schemes,and safety of water projects through accelerating the hydrological cycle.Under the global warming,due to the sea level rise,the increase in frequency and intensity of extreme storms and droughts,the design standards need to be improved to some extent.The long-term drought will significantly affect the safety operation of water projects,meanwhile,the extremely durative heat wave or cold wave will possibly reduce the factor of safety of dams as well.
The climate change is one of the important environmental issues,and water conservancy projects are main measures to cope with the climate change.The climate change will have effect on the design standards,operation schemes,and safety of water projects through accelerating the hydrological cycle.Under the global warming,due to the sea level rise,the increase in frequency and intensity of extreme storms and droughts,the design standards need to be improved to some extent.The long-term drought will significantly affect the safety operation of water projects,meanwhile,the extremely durative heat wave or cold wave will possibly reduce the factor of safety of dams as well.
Abstract：
The influence of interface friction on the soil tests can’t be neglected,and its value has certain effects on the reliability of the test results,so the magnitude of its value and the measures become the universal issue.At present,there isn’t any kind of good test method to measure the friction between samples and the load structures(steel structures) and to study the measures.A kind of test equipment is developed,and designed systematic tests on granular materials are carried out.The test method of interface friction,the frictional values of granular materials,and the validity of measures are discussed.The tests indicate that there is an proportional relationship between the friction and the normal pressure.The friction coefficient reaches about 0.45.After certain measures are taken,it may fall to 0.1.It’s extremely difficult to eliminate the fiction in a greater degree.Therefore,the interface friction should be considered in the design of the soil tests and in the analysis of the test results.
The influence of interface friction on the soil tests can’t be neglected,and its value has certain effects on the reliability of the test results,so the magnitude of its value and the measures become the universal issue.At present,there isn’t any kind of good test method to measure the friction between samples and the load structures(steel structures) and to study the measures.A kind of test equipment is developed,and designed systematic tests on granular materials are carried out.The test method of interface friction,the frictional values of granular materials,and the validity of measures are discussed.The tests indicate that there is an proportional relationship between the friction and the normal pressure.The friction coefficient reaches about 0.45.After certain measures are taken,it may fall to 0.1.It’s extremely difficult to eliminate the fiction in a greater degree.Therefore,the interface friction should be considered in the design of the soil tests and in the analysis of the test results.
Abstract：
Through adjusting the working parameters of temperature and humidity in the constant temperature and humidity equipments,the state variation of saturated expansive soil under different drying rates is achieved.The influences of the drying rates on shrinkage,strength and water retention characteristics of expensive soil are investigated,in which the shrinkage tests and the unsaturated triaxial tests are employed.The experimental results indicate that the coefficient of shrinkage increases as the drying rate decreases,and that the drying process is linear at the beginning and then becomes nonlinear.Moreover,the suction strength of unsaturated expansive soil increases as the drying rate decreases under the same water content,which is more prominent especially under the condition of low moisture content and confined pressure.Based on the expression of power function relationship between suction strength and suction,a bi-linear water retention curve is back-calculated from the coefficient of shrinkage and suction strength.It is found that the drop part of water retention characteristic curve tends to approximate parallel under various drying rates.The smaller the drying rates,the greater the air-entry value and suction.
Through adjusting the working parameters of temperature and humidity in the constant temperature and humidity equipments,the state variation of saturated expansive soil under different drying rates is achieved.The influences of the drying rates on shrinkage,strength and water retention characteristics of expensive soil are investigated,in which the shrinkage tests and the unsaturated triaxial tests are employed.The experimental results indicate that the coefficient of shrinkage increases as the drying rate decreases,and that the drying process is linear at the beginning and then becomes nonlinear.Moreover,the suction strength of unsaturated expansive soil increases as the drying rate decreases under the same water content,which is more prominent especially under the condition of low moisture content and confined pressure.Based on the expression of power function relationship between suction strength and suction,a bi-linear water retention curve is back-calculated from the coefficient of shrinkage and suction strength.It is found that the drop part of water retention characteristic curve tends to approximate parallel under various drying rates.The smaller the drying rates,the greater the air-entry value and suction.
Abstract：
Based on a number of oedometer tests on 13 soil samples,the influence of repeated loading on the secondary consolidation properties is investigated.It is found that with the increase of consolidation pressure p,the secondary consolidation coefficient C■ increases firstly to a maximum value and then decreases under initial loading,but the consolidation pressure corresponding to the maximum value is not equal to the preconsolidation pressure.It is also revealed that with the increase of p,C■ decreases under the first reloading and increases after 35 cycles in overconsolidated state.With the increase of loading cycle number,C■ decreases significantly.The load ratio △p/p has significant effects on C■.Experimental findings and results are significant to the settlement control of soft soil ground.
Based on a number of oedometer tests on 13 soil samples,the influence of repeated loading on the secondary consolidation properties is investigated.It is found that with the increase of consolidation pressure p,the secondary consolidation coefficient C■ increases firstly to a maximum value and then decreases under initial loading,but the consolidation pressure corresponding to the maximum value is not equal to the preconsolidation pressure.It is also revealed that with the increase of p,C■ decreases under the first reloading and increases after 35 cycles in overconsolidated state.With the increase of loading cycle number,C■ decreases significantly.The load ratio △p/p has significant effects on C■.Experimental findings and results are significant to the settlement control of soft soil ground.
Abstract：
Centrifugal model tests and numerical simulation are conducted to investigate behaviors of ground settlement due to groundwater exploitation and to demonstrate the influence of land subsidence on three types of bridges.By use of the elasto-plastic finite element analysis method,the structural transformation of the bridge in the typical section of the high speed railway with the influence of land subsidence is studied.At the center district of land subsidence and in the vicinity of the well,the asymmetrical subsidence is more serious,and has larger influence on the bridge structure than the regional land subsidence does.It can be prevented and cured by adopting engineering measures.
Centrifugal model tests and numerical simulation are conducted to investigate behaviors of ground settlement due to groundwater exploitation and to demonstrate the influence of land subsidence on three types of bridges.By use of the elasto-plastic finite element analysis method,the structural transformation of the bridge in the typical section of the high speed railway with the influence of land subsidence is studied.At the center district of land subsidence and in the vicinity of the well,the asymmetrical subsidence is more serious,and has larger influence on the bridge structure than the regional land subsidence does.It can be prevented and cured by adopting engineering measures.
2009, 31(3): 353-360.
Abstract：
On the basis of the framework of internal variable quasi-thermodynamics,the relationship between viscosity theory and plasticity theory is studied.Assuming that the reference point at the reference equivalent time line is an initial loading point and the effective stress is abruptly loaded on clay,some behaviors of the iso-time lines derived from Yin-Graham’s 1-D elastic visco-plastic model are analyzed.The scope that new Hypothesis A is approximately equivalent to Hypothesis B is obtained and the flaws of the original Hypothesis A are pointed out.When the loading effective stress is 1.1 times larger than the initial effective stress and the duration time is larger than the reference absolute equivalent time,the absolute equivalent time is approximately equal to the duration time.The strain of clay is the sum of plasto-elastic strain and fractional creep strain,in which the plasto-elastic strain depends on effective stress and is independent of time,while the fractional creep strain depends on time,but not on effective stress.By means of the theory of internal variable quasi-thermodynamics,the internal relation of Lagrange’s dissipative rate function between the 1-D EVP model and a pure plastic model is demonstrated and the reason why the 1-D EVP model has quasi-plastic visco-elastic characteristics is revealed.A 3-D EVP model is generalized from the 1-D EVP model according to the rule of Lagrange’s dissipative rate function occurring in the 1-D EVP model.Compared with experimental data obtained from consolidation-undrained triaxial shear creep test,the present 3-D EVP model is verified to be valid.
On the basis of the framework of internal variable quasi-thermodynamics,the relationship between viscosity theory and plasticity theory is studied.Assuming that the reference point at the reference equivalent time line is an initial loading point and the effective stress is abruptly loaded on clay,some behaviors of the iso-time lines derived from Yin-Graham’s 1-D elastic visco-plastic model are analyzed.The scope that new Hypothesis A is approximately equivalent to Hypothesis B is obtained and the flaws of the original Hypothesis A are pointed out.When the loading effective stress is 1.1 times larger than the initial effective stress and the duration time is larger than the reference absolute equivalent time,the absolute equivalent time is approximately equal to the duration time.The strain of clay is the sum of plasto-elastic strain and fractional creep strain,in which the plasto-elastic strain depends on effective stress and is independent of time,while the fractional creep strain depends on time,but not on effective stress.By means of the theory of internal variable quasi-thermodynamics,the internal relation of Lagrange’s dissipative rate function between the 1-D EVP model and a pure plastic model is demonstrated and the reason why the 1-D EVP model has quasi-plastic visco-elastic characteristics is revealed.A 3-D EVP model is generalized from the 1-D EVP model according to the rule of Lagrange’s dissipative rate function occurring in the 1-D EVP model.Compared with experimental data obtained from consolidation-undrained triaxial shear creep test,the present 3-D EVP model is verified to be valid.
Abstract：
During the coupled thermal-hydro-mechanical analysis of porous media,the porosity and viscosity of porous water are the main factors affecting the permeability of the rock mass.Based on the variation law of porosity and viscosity of porous water undertaking loads,a method of stress-dependent porosity and temperature-dependent viscosity of porous water is developed during the numerical analysis.To investigate the influence of mechanical boundary conditions on the thermal stress,a comparison of the results between displacement boundary and stress boundary is made.The study indicates that the values of thermal stress and pore pressure obtained by stress boundary are smaller than those by displacement boundary.The calculated values of pore pressure taking nonlinear seepage behavior into account are closer to the measured ones.
During the coupled thermal-hydro-mechanical analysis of porous media,the porosity and viscosity of porous water are the main factors affecting the permeability of the rock mass.Based on the variation law of porosity and viscosity of porous water undertaking loads,a method of stress-dependent porosity and temperature-dependent viscosity of porous water is developed during the numerical analysis.To investigate the influence of mechanical boundary conditions on the thermal stress,a comparison of the results between displacement boundary and stress boundary is made.The study indicates that the values of thermal stress and pore pressure obtained by stress boundary are smaller than those by displacement boundary.The calculated values of pore pressure taking nonlinear seepage behavior into account are closer to the measured ones.
Abstract：
The liquid phase,a very active part in the soil body,can change the connections among particles through the isolation of solution ingredient in the pore and the dissolving of granular mineral,then influence the structural intensity of the soil body.Based on the laboratory test that changes the kind and content of the solution in the clay structural pore,the mechanical behavior under thermal effect of different soluble salt ingredients in the soil structural pore is discussed.The influence of ingredients and content of pore solution on structural and mechanical behavior of viscous soil under thermal effect is studied.The test results show that when the temperature increases from 40℃ to 6 0℃,the time of thermal effect is 16 8 h,the cohesion of the clay added MgCl2 ingredients has the greatest increasing range,followed by that of the clay added Fe and MnSO4 ingredients,and that of the clay added FeCl3 ingredients has a little increasing range.On the contrary,the cohesion becomes smaller after adding Ca(OH)2.Under the same condition,the internal friction angle of the clay added FeCl3 and Na2S2O4 ingredients is reduced,the group added Fe and AlCl3 has a little change,and the increasing range of clay added MgCl2 is similar to that added Ca(OH)2,second only to the clay soaked with deionized water.
The liquid phase,a very active part in the soil body,can change the connections among particles through the isolation of solution ingredient in the pore and the dissolving of granular mineral,then influence the structural intensity of the soil body.Based on the laboratory test that changes the kind and content of the solution in the clay structural pore,the mechanical behavior under thermal effect of different soluble salt ingredients in the soil structural pore is discussed.The influence of ingredients and content of pore solution on structural and mechanical behavior of viscous soil under thermal effect is studied.The test results show that when the temperature increases from 40℃ to 6 0℃,the time of thermal effect is 16 8 h,the cohesion of the clay added MgCl2 ingredients has the greatest increasing range,followed by that of the clay added Fe and MnSO4 ingredients,and that of the clay added FeCl3 ingredients has a little increasing range.On the contrary,the cohesion becomes smaller after adding Ca(OH)2.Under the same condition,the internal friction angle of the clay added FeCl3 and Na2S2O4 ingredients is reduced,the group added Fe and AlCl3 has a little change,and the increasing range of clay added MgCl2 is similar to that added Ca(OH)2,second only to the clay soaked with deionized water.
Abstract：
The bridge pile foundation in high-steep rock slopes has double functions that will not only bear the load from the superstructure,but also counteract the landslide-thrust from the pile foundation side.The bearing mechanism of piles in high-steep rock slopes is much more complex than that of piles in the flat because of the steep rock slope.Based on the bending differential equation of pile foundation under vertical load piles,the similarity rule of the bridge pile foundation in steep slopes is deduced and model tests are implemented on the basis of the similarity rule.The moment and horizontal displacements are achieved through different combined loads and load methods,the working mechanism of the pile foundation is discussed,and the distribution and influence zone of soil thrust and resistance is acquired by model tests.It will help to deeply understand the load transfer mechanism.
The bridge pile foundation in high-steep rock slopes has double functions that will not only bear the load from the superstructure,but also counteract the landslide-thrust from the pile foundation side.The bearing mechanism of piles in high-steep rock slopes is much more complex than that of piles in the flat because of the steep rock slope.Based on the bending differential equation of pile foundation under vertical load piles,the similarity rule of the bridge pile foundation in steep slopes is deduced and model tests are implemented on the basis of the similarity rule.The moment and horizontal displacements are achieved through different combined loads and load methods,the working mechanism of the pile foundation is discussed,and the distribution and influence zone of soil thrust and resistance is acquired by model tests.It will help to deeply understand the load transfer mechanism.
Abstract：
The anti-explosion model test methods are adopted to study the anchoring effect of the tunnels reinforced by dense rock bolts at arch top under the explosive stress waves produced by focus charging.According to pressure temporal curves,it is proved that the test data are proper and reliable.For the purpose of the comparison of anchoring effects between the dense rock bolts at arch top and the common rock bolts,the differences of the arch vault displacement,the surface strain,the acceleration of roof and floor and the damage shape of the two underground openings are analyzed.The results show that the anchoring effect of dense bolts at arch top is not good.
The anti-explosion model test methods are adopted to study the anchoring effect of the tunnels reinforced by dense rock bolts at arch top under the explosive stress waves produced by focus charging.According to pressure temporal curves,it is proved that the test data are proper and reliable.For the purpose of the comparison of anchoring effects between the dense rock bolts at arch top and the common rock bolts,the differences of the arch vault displacement,the surface strain,the acceleration of roof and floor and the damage shape of the two underground openings are analyzed.The results show that the anchoring effect of dense bolts at arch top is not good.
Abstract：
Based on the mechanism of evapotranspiration(ET) covers,the plant interception,soil evaporation,ET,runoff and net infiltration are calculated considering the Penman’s potential ET.The calculated net infiltration is input into unsaturated flow models as boundary conditions to simulate the moisture transport and evaluate the performance of a monolithic cover and a capillary cover.The analytic results show that the ET is crucial to the moisture transport in ET covers.The moisture content of shallow soils is sensitive to the variation of rainfall and ET,whereas the moisture content of soils in the bottom remains almost unchanged.The storage and release of infiltrated water happen mainly within the root depth.The ET covers with a good stand of plants and a root depth of 50 cm are applicable to the Yangtze River delta region.The ET covers have advantages over conventional landfill covers in reducing rainfall percolation.
Based on the mechanism of evapotranspiration(ET) covers,the plant interception,soil evaporation,ET,runoff and net infiltration are calculated considering the Penman’s potential ET.The calculated net infiltration is input into unsaturated flow models as boundary conditions to simulate the moisture transport and evaluate the performance of a monolithic cover and a capillary cover.The analytic results show that the ET is crucial to the moisture transport in ET covers.The moisture content of shallow soils is sensitive to the variation of rainfall and ET,whereas the moisture content of soils in the bottom remains almost unchanged.The storage and release of infiltrated water happen mainly within the root depth.The ET covers with a good stand of plants and a root depth of 50 cm are applicable to the Yangtze River delta region.The ET covers have advantages over conventional landfill covers in reducing rainfall percolation.
Abstract：
In order to fully understand the influences of different supporting opportunities on the mechanical characteristics of soft-weak surrounding rocks in highway tunnels,the developed geomechanical model tests as well as the simple and practical tools and methods adopted in tunnel excavation are used.The highway tunnel model tests are systematically launched based on the idea of construction after loading.The influences of supporting opportunity on the surrounding pressure,the size and the distribution of shear stress of lining in soft-weak rocks in highway tunnels are studied.The results show that the influences are notable,and a 200 mm reserved deformation is reasonable when the excavation diameter is about 12 m under different stress fields in soft-weak surrounding rocks(the elastic modulus of surrounding rocks is 210 MPa).Under such conditions,the shear stress and the surrounding stress are lower,and the distribution is also comparatively homogeneous,which is the most beneficial to lining force.In the actual project we should strengthen monitoring and measurement,sum up experience and choose the best opportunity to achieve smaller stress of lining as far as possible.
In order to fully understand the influences of different supporting opportunities on the mechanical characteristics of soft-weak surrounding rocks in highway tunnels,the developed geomechanical model tests as well as the simple and practical tools and methods adopted in tunnel excavation are used.The highway tunnel model tests are systematically launched based on the idea of construction after loading.The influences of supporting opportunity on the surrounding pressure,the size and the distribution of shear stress of lining in soft-weak rocks in highway tunnels are studied.The results show that the influences are notable,and a 200 mm reserved deformation is reasonable when the excavation diameter is about 12 m under different stress fields in soft-weak surrounding rocks(the elastic modulus of surrounding rocks is 210 MPa).Under such conditions,the shear stress and the surrounding stress are lower,and the distribution is also comparatively homogeneous,which is the most beneficial to lining force.In the actual project we should strengthen monitoring and measurement,sum up experience and choose the best opportunity to achieve smaller stress of lining as far as possible.
Abstract：
Restricted by the assumption of low-order linear displacement approximation in each block,Discrete Element Methods(including DDA) often have to mesh many continuum parts of the problem domain into small discrete blocks when simulating crack propagation problems,and the result is very sensitive to the very way that divides the domain.In order to construct the block system with physical structural planes as consistently as possible and improve precision of displacements and stresses results,it is indispensable to introduce new efficient displacement approximations.This method newly introduces meshfree approximations,meshfree nodal displacements are taken as the degrees of freedom instead of block rigid movements and strains.Based on this improvement,analysis of cracks’ propagation inside blocks can be conducted.The detailed algorithm on analyzing cracks exploration inside blocks is: enriched approximations which describe singular crack tips fields and discontinuous crack faces are employed under the Partition of Unity theory;the enriched nodes surrounding crack tips or faces are respectively mapped with corresponding enriched degrees of freedom,and the solution of all these degrees of freedom is uniformly proceeded by the implicit iteration algorithm of DDA,then fracture and breakage of DDA blocks can be analyzed.The numeric examples show this algorithm is rational and efficient.
Restricted by the assumption of low-order linear displacement approximation in each block,Discrete Element Methods(including DDA) often have to mesh many continuum parts of the problem domain into small discrete blocks when simulating crack propagation problems,and the result is very sensitive to the very way that divides the domain.In order to construct the block system with physical structural planes as consistently as possible and improve precision of displacements and stresses results,it is indispensable to introduce new efficient displacement approximations.This method newly introduces meshfree approximations,meshfree nodal displacements are taken as the degrees of freedom instead of block rigid movements and strains.Based on this improvement,analysis of cracks’ propagation inside blocks can be conducted.The detailed algorithm on analyzing cracks exploration inside blocks is: enriched approximations which describe singular crack tips fields and discontinuous crack faces are employed under the Partition of Unity theory;the enriched nodes surrounding crack tips or faces are respectively mapped with corresponding enriched degrees of freedom,and the solution of all these degrees of freedom is uniformly proceeded by the implicit iteration algorithm of DDA,then fracture and breakage of DDA blocks can be analyzed.The numeric examples show this algorithm is rational and efficient.
Abstract：
Soil unloading and rebound induced by large-scale deep excavation may affect the performance and integrity of existing piles inside the excavation zone,especially for up-lift piles.The non-linear finite element is employed to investigate the behavior of the up-lift piles in Shanghai Expo Underground Substation Project during deep excavation.Parameters of the subsoil are obtained by inverse analysis of the load tests on the up-lift piles.The behavior of the up-lift piles during deep excavation and under normal working load is analyzed by using the parameters.Results show that the tension force induced by excavation exerts a more negative influence on up-lift piles than normal piles.Therefore this pretension should be taken into consideration during pile design.Analysis shows the bottom-enlarged up-lift piles are subjected to a larger pretension force during excavation than ordinary up-lift piles.The pretension force of piles under working load can be deduced from the combination of the tension force induced by excavation and the tension force induced by working load.
Soil unloading and rebound induced by large-scale deep excavation may affect the performance and integrity of existing piles inside the excavation zone,especially for up-lift piles.The non-linear finite element is employed to investigate the behavior of the up-lift piles in Shanghai Expo Underground Substation Project during deep excavation.Parameters of the subsoil are obtained by inverse analysis of the load tests on the up-lift piles.The behavior of the up-lift piles during deep excavation and under normal working load is analyzed by using the parameters.Results show that the tension force induced by excavation exerts a more negative influence on up-lift piles than normal piles.Therefore this pretension should be taken into consideration during pile design.Analysis shows the bottom-enlarged up-lift piles are subjected to a larger pretension force during excavation than ordinary up-lift piles.The pretension force of piles under working load can be deduced from the combination of the tension force induced by excavation and the tension force induced by working load.
Abstract：
Based on Biot’s consolidation equation,the horizontal vibration of an end bearing pile embedded in saturated soil is investigated.The potential functions are introduced to decouple the governing differential equations,then by virtue of the differential operator splitting and variable separation method,the horizontal dynamical characteristics under steady state of pile-soil interaction are obtained with the assumption of perfect contact between the pile and the soil.The comparisons with the equivalent single-phase solution and the tow-phase solution are presented.A parametric study is conducted to determine the main features of pile-soil interaction in horizontal vibration.As a result,the permeability coefficient has certain effects on the impedance of rocking,horizontal and coupled horizontal-rocking vibrations of the single pile,and the condition of the solution that can be equivalent to the equivalent single-phase solution is put forward.
Based on Biot’s consolidation equation,the horizontal vibration of an end bearing pile embedded in saturated soil is investigated.The potential functions are introduced to decouple the governing differential equations,then by virtue of the differential operator splitting and variable separation method,the horizontal dynamical characteristics under steady state of pile-soil interaction are obtained with the assumption of perfect contact between the pile and the soil.The comparisons with the equivalent single-phase solution and the tow-phase solution are presented.A parametric study is conducted to determine the main features of pile-soil interaction in horizontal vibration.As a result,the permeability coefficient has certain effects on the impedance of rocking,horizontal and coupled horizontal-rocking vibrations of the single pile,and the condition of the solution that can be equivalent to the equivalent single-phase solution is put forward.
Abstract：
A soil engineering classification derived from the piezocone penetration test(CPTU) involves the uncertainty of correlation between soil composition and soil mechanical behavior.This uncertainty results in overlaps of different soil types in currently used CPTU soil classification systems.The cluster analysis is a statistical method for grouping similar mathematical data sets and is used herein for illustrating the soil stratigraphy from CPTU data.Its application to defining stratigraphic interfaces is illustrated using five expressway case studies with layered vertical profiles.It is concluded that the cluster analysis is not only able to delineate major changes within the stratigraphy but also detect thin layers within a sublayer.Therefore,the cluster analysis can provide valid and reliable preliminary soil stratification based upon the CPTU original data.
A soil engineering classification derived from the piezocone penetration test(CPTU) involves the uncertainty of correlation between soil composition and soil mechanical behavior.This uncertainty results in overlaps of different soil types in currently used CPTU soil classification systems.The cluster analysis is a statistical method for grouping similar mathematical data sets and is used herein for illustrating the soil stratigraphy from CPTU data.Its application to defining stratigraphic interfaces is illustrated using five expressway case studies with layered vertical profiles.It is concluded that the cluster analysis is not only able to delineate major changes within the stratigraphy but also detect thin layers within a sublayer.Therefore,the cluster analysis can provide valid and reliable preliminary soil stratification based upon the CPTU original data.
Abstract：
Based on the example of Shenzhen shield tunneling under a cable tunnel,through application of the displacement load method to simulate the tunnel excavation and by use of the beam theory of elastic foundation to analyze pipe-soil interaction,the existing tunnel above the subway tunnel considered as a large-diameter pipeline is proposed.The formation response caused by the construction of the left line of the subway is analyzed.The safety of the cable tunnel is evaluated by the relative control standards.It is shown that the numerical results agree well with the measured data,and the cable tunnel is also in a state of safety.It can provide reference for similar projects.
Based on the example of Shenzhen shield tunneling under a cable tunnel,through application of the displacement load method to simulate the tunnel excavation and by use of the beam theory of elastic foundation to analyze pipe-soil interaction,the existing tunnel above the subway tunnel considered as a large-diameter pipeline is proposed.The formation response caused by the construction of the left line of the subway is analyzed.The safety of the cable tunnel is evaluated by the relative control standards.It is shown that the numerical results agree well with the measured data,and the cable tunnel is also in a state of safety.It can provide reference for similar projects.
Abstract：
The rigid limit equilibrium method has been widely used to analyze the wedge stability.However,it does not satisfy equilibrium equations,and it still requires assumptions regarding the force reactions,which may result in false results.A new method based on the lower bound method to analyze the stability of wedge slopes is proposed.It does not require assumptions regarding the wedge failure mode,the force reactions or the number of slide planes.The block-structural plane model is used for constructing the statically admissible stress fields which satisfy the equilibrium conditions,boundary conditions and yield criteria.By using the idea of nonlinear programming,the lower bound limit analysis model of mathematical programming for wedge stability is established.Finally,three examples are used,and the results agree well with those from the finite element and the upper bound methods.
The rigid limit equilibrium method has been widely used to analyze the wedge stability.However,it does not satisfy equilibrium equations,and it still requires assumptions regarding the force reactions,which may result in false results.A new method based on the lower bound method to analyze the stability of wedge slopes is proposed.It does not require assumptions regarding the wedge failure mode,the force reactions or the number of slide planes.The block-structural plane model is used for constructing the statically admissible stress fields which satisfy the equilibrium conditions,boundary conditions and yield criteria.By using the idea of nonlinear programming,the lower bound limit analysis model of mathematical programming for wedge stability is established.Finally,three examples are used,and the results agree well with those from the finite element and the upper bound methods.
Abstract：
Based on the method of finite layer of Biot’s consolidation of elastic soil,by means of the elastic-viscoelastic correspondence principle and Laplace transform,the method of finite layer of Biot’s consolidation of viscoelastic soil is presented and programmed.An example of viscoelastic foundation settlement shows the present method and programme are true.With the increase of viscosity coefficient,the viscosity of materials plays a great rloe.It is in good agreement with the choosen viscoelastic model.The relationship between the effect of consolidation and the viscosity is analyzed.
Based on the method of finite layer of Biot’s consolidation of elastic soil,by means of the elastic-viscoelastic correspondence principle and Laplace transform,the method of finite layer of Biot’s consolidation of viscoelastic soil is presented and programmed.An example of viscoelastic foundation settlement shows the present method and programme are true.With the increase of viscosity coefficient,the viscosity of materials plays a great rloe.It is in good agreement with the choosen viscoelastic model.The relationship between the effect of consolidation and the viscosity is analyzed.
Abstract：
In order to study the destressing effects of the deep thick coal seams with high burst liability after mining upper and lower protective seams,the method of similar material simulation experiment is adopted to analyze the rule of the stress change,to compute the lower reasonable distressing angle of the lower protective seam,and to find the lower tunnel’s reasonable position of the protected seam by monitoring the stress change of the protected seam in the process of mining the protective seam and the stable state.The reasonable position of the upper protective seam workface is chosen by comparing the distressing effects of the twice simulation experiments of mining the upper protective seam.The upper tunnel region of the protected seam is still a high concentrative area with easy occurrence of rock burst despite mining the lower protective seam.After mining the upper protective seam,the stress in this area falls obviously,so it proves that the upper protective seam distresses obviously.The experiment verifies that the "rebound" phenomenon occurs on the earth surface before rock burst with high energy in mining.This study provides the theoretical guidance for the mining design of the workface and it is very important to prevent rock burst in practice.
In order to study the destressing effects of the deep thick coal seams with high burst liability after mining upper and lower protective seams,the method of similar material simulation experiment is adopted to analyze the rule of the stress change,to compute the lower reasonable distressing angle of the lower protective seam,and to find the lower tunnel’s reasonable position of the protected seam by monitoring the stress change of the protected seam in the process of mining the protective seam and the stable state.The reasonable position of the upper protective seam workface is chosen by comparing the distressing effects of the twice simulation experiments of mining the upper protective seam.The upper tunnel region of the protected seam is still a high concentrative area with easy occurrence of rock burst despite mining the lower protective seam.After mining the upper protective seam,the stress in this area falls obviously,so it proves that the upper protective seam distresses obviously.The experiment verifies that the "rebound" phenomenon occurs on the earth surface before rock burst with high energy in mining.This study provides the theoretical guidance for the mining design of the workface and it is very important to prevent rock burst in practice.
Abstract：
For the numerical analysis of elastic foundation beams working together with ground,the traditional methods of Winkler’s or double-parameter model have some limitations in engineering.In order to consider the limitation at beam borders and stress diffusion in soil,the process of dummy nodes at beam borders,the control equations and their finite difference schemes are given.The examples by use of computer programs show the effect of beams working together with ground at the borders of the beams and the stress diffuse in soil.The present method can be used to analyze the beam stress in design of foundation engineering.
For the numerical analysis of elastic foundation beams working together with ground,the traditional methods of Winkler’s or double-parameter model have some limitations in engineering.In order to consider the limitation at beam borders and stress diffusion in soil,the process of dummy nodes at beam borders,the control equations and their finite difference schemes are given.The examples by use of computer programs show the effect of beams working together with ground at the borders of the beams and the stress diffuse in soil.The present method can be used to analyze the beam stress in design of foundation engineering.
Abstract：
In order to make further researches on the new types of piles,a large-scale pile foundation system is established to make full-scale model tests and overcome the disadvantages of small model tests,such as scale effect.The developed system consists of the test room,loading system,measuring system and soils.The preparing method of soils,including control indices,laying methods and result detecting,is introduced.Meanwhile the pile-making method and quality test method are also shown.The final test results show that the quality of the soils can meet the requirements of the following experiments.Furthermore,by use of this model test system,the full-scale load tests on PCC piles are done,and the results indicate that the full-scale pile foundation test is feasible.
In order to make further researches on the new types of piles,a large-scale pile foundation system is established to make full-scale model tests and overcome the disadvantages of small model tests,such as scale effect.The developed system consists of the test room,loading system,measuring system and soils.The preparing method of soils,including control indices,laying methods and result detecting,is introduced.Meanwhile the pile-making method and quality test method are also shown.The final test results show that the quality of the soils can meet the requirements of the following experiments.Furthermore,by use of this model test system,the full-scale load tests on PCC piles are done,and the results indicate that the full-scale pile foundation test is feasible.
Abstract：
The key character of dispersive clay is to be dispersed and wrecked by water flows,causing serious threats to engineering safety.But those studies on dispersive clay,such as the methods of identification,dispersive mechanism and their applications,are still not deep enough and satisfactory due to their trivial discovery and few engineering practices.Based on the analysis of physical and chemical characters and mineralogical composition,the dispersivity and dispersive mechanism of the dam soil samples in Wenjiagou Reservoir are studied by double-hydrometer tests,pore water salts tests,pinhole tests,crumb tests and exchangeable sodium percentage tests,and further investigations on the impermeability of soil samples are also carried out by itself and under the protection of inverted filter materials.The results show that soil samples are transitional and dispersive soil because of rich montmorillonoid,plenty of sodium-ion and strong alkalescence.The soil samples have weak self-impermeability,but favorable impermeability under the protection of the inverted filter materials.The studies indicate that soil becomes dispersive clay only under the conditions of rich montmorillonoid contents,more sodium-ion and strong alkalescence,and the dispersive clay presents a better seepage prevention under the protection of appropriate inverted filter materials.
The key character of dispersive clay is to be dispersed and wrecked by water flows,causing serious threats to engineering safety.But those studies on dispersive clay,such as the methods of identification,dispersive mechanism and their applications,are still not deep enough and satisfactory due to their trivial discovery and few engineering practices.Based on the analysis of physical and chemical characters and mineralogical composition,the dispersivity and dispersive mechanism of the dam soil samples in Wenjiagou Reservoir are studied by double-hydrometer tests,pore water salts tests,pinhole tests,crumb tests and exchangeable sodium percentage tests,and further investigations on the impermeability of soil samples are also carried out by itself and under the protection of inverted filter materials.The results show that soil samples are transitional and dispersive soil because of rich montmorillonoid,plenty of sodium-ion and strong alkalescence.The soil samples have weak self-impermeability,but favorable impermeability under the protection of the inverted filter materials.The studies indicate that soil becomes dispersive clay only under the conditions of rich montmorillonoid contents,more sodium-ion and strong alkalescence,and the dispersive clay presents a better seepage prevention under the protection of appropriate inverted filter materials.
Abstract：
Particle breakage of rockfill materials is serious under high pressure,and its influence on deformation of rockfill cannot be ignored.A method is presented to make artificial rockfill materials with ellipse-shaped particles,which are moulded in various sizes and strengths with cement pastes.Based on a series of triaxial tests,the behaviour of stress-strain and breakage volumetric strain of artificial rockfill materials is analyzed.The test results show that the relative breakage is correlative to the particle strength and confining pressure.The stress-strain behaviour of rockfill is seriously influenced by the particle breakage.The breakage volumetric strain of rockfill is positive and increases with the increase of axial strain in a trend of hyperbolic curve.The relationship between the breakage volumetric strain and the relative breakage can be fitted by a power function.
Particle breakage of rockfill materials is serious under high pressure,and its influence on deformation of rockfill cannot be ignored.A method is presented to make artificial rockfill materials with ellipse-shaped particles,which are moulded in various sizes and strengths with cement pastes.Based on a series of triaxial tests,the behaviour of stress-strain and breakage volumetric strain of artificial rockfill materials is analyzed.The test results show that the relative breakage is correlative to the particle strength and confining pressure.The stress-strain behaviour of rockfill is seriously influenced by the particle breakage.The breakage volumetric strain of rockfill is positive and increases with the increase of axial strain in a trend of hyperbolic curve.The relationship between the breakage volumetric strain and the relative breakage can be fitted by a power function.
Abstract：
In order to study the reinforcement and load transfer mechanism of anchors in slopes,the dual-spring element is adopted to simulate the characteristics of anchors.A numerical model for slopes reinforced by anchors is founded by FLAC3D.The effects of anchors length on the safety factor and slip plane of slopes are analyzed as well as the mechanical response of anchors.The results show that,in the slope with anchors reinforcement,there exists an effective length;with the increase of anchors length,the potential slip plane moves towards the inside of slopes,and failure mode transfers from the shallow slip to the deep slip;when the length reaches the effective reinforcement length,the location of the slip plane changes abruptly;the axial forces at each layer distribute differently along the anchor;if the material of slopes becomes weaker after the disturbance of outer load,the anchors in the lower part of slopes exhibit the maximum axial force;so it is necessary to lengthen the anchors in these places for the slopes with permanent reinforcement of anchors.
In order to study the reinforcement and load transfer mechanism of anchors in slopes,the dual-spring element is adopted to simulate the characteristics of anchors.A numerical model for slopes reinforced by anchors is founded by FLAC3D.The effects of anchors length on the safety factor and slip plane of slopes are analyzed as well as the mechanical response of anchors.The results show that,in the slope with anchors reinforcement,there exists an effective length;with the increase of anchors length,the potential slip plane moves towards the inside of slopes,and failure mode transfers from the shallow slip to the deep slip;when the length reaches the effective reinforcement length,the location of the slip plane changes abruptly;the axial forces at each layer distribute differently along the anchor;if the material of slopes becomes weaker after the disturbance of outer load,the anchors in the lower part of slopes exhibit the maximum axial force;so it is necessary to lengthen the anchors in these places for the slopes with permanent reinforcement of anchors.
Abstract：
The roadbed problems of railways are very serious in the permafrost regions of Northeast China.Manifold measures are applied in the experimental project to solve the roadbed problems based on the successful experience of Qinghai-Tibet Railway.There are two sections(274K500 m～275K000 m,275K460～276K000 m) in the experimental project in the north region of Yaling Railway.Some active measures such as insulated materials(XPS,EPS) and two-phase closed thermosyphons are applied in these two sections.The ground temperature data of long-term monitoring of the experimental project indicate that the measures can effectively reduce the ground temperature of the permafrost under the roadbed and the thickness of the active layer.And the analytic results indicate that the measures are helpful to the stability of railways.
The roadbed problems of railways are very serious in the permafrost regions of Northeast China.Manifold measures are applied in the experimental project to solve the roadbed problems based on the successful experience of Qinghai-Tibet Railway.There are two sections(274K500 m～275K000 m,275K460～276K000 m) in the experimental project in the north region of Yaling Railway.Some active measures such as insulated materials(XPS,EPS) and two-phase closed thermosyphons are applied in these two sections.The ground temperature data of long-term monitoring of the experimental project indicate that the measures can effectively reduce the ground temperature of the permafrost under the roadbed and the thickness of the active layer.And the analytic results indicate that the measures are helpful to the stability of railways.
