2000 Vol. 22 No. 6
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2000, 22(6): 639-642.
Abstract：
Three tunneling methods in the saturated loess for the project of water transferring from south to north of China are numerically tested and discussed with the introduced Austria software FINAL.The numercial results demonstrate:(1)Tunneling with NATM (CASE A) is possible and the 10+15 cm shotcrete immediately following the excavation is absolutely necessary ;(2)The interaction between two parallel tunneling caves with a distance of 2.5 times of tunnel diameter can be ignored ;(3)Instead of projecting concrete support to strengthen the surrounding loess of the tunnel,the traditional tunneling method(CASE B) in which the cast in site lining system is introduced to support the loess,is also possible for the local simple constructors,although the settelements of the tunnel crown reached 141 mm;(4)To reduce the tunnel settlements,another tunneling method(CASE C) with the precast lining system constructed before the tunnel excavation,is much better than CASE B with settlements of 8.5 mm, although the precast lining technics is much complex than CASE B.(5)All the feasible tunneling methods are based on the effective drainage of the water from the current level to the bottom of the tunnel.
Three tunneling methods in the saturated loess for the project of water transferring from south to north of China are numerically tested and discussed with the introduced Austria software FINAL.The numercial results demonstrate:(1)Tunneling with NATM (CASE A) is possible and the 10+15 cm shotcrete immediately following the excavation is absolutely necessary ;(2)The interaction between two parallel tunneling caves with a distance of 2.5 times of tunnel diameter can be ignored ;(3)Instead of projecting concrete support to strengthen the surrounding loess of the tunnel,the traditional tunneling method(CASE B) in which the cast in site lining system is introduced to support the loess,is also possible for the local simple constructors,although the settelements of the tunnel crown reached 141 mm;(4)To reduce the tunnel settlements,another tunneling method(CASE C) with the precast lining system constructed before the tunnel excavation,is much better than CASE B with settlements of 8.5 mm, although the precast lining technics is much complex than CASE B.(5)All the feasible tunneling methods are based on the effective drainage of the water from the current level to the bottom of the tunnel.
2000, 22(6): 643-649.
Abstract：
On the basis of decadal measurement this paper analyzes the settlement of railway on soft clay ground in Lianyungang.Besides it accurately predicts residual settlement after construction.According to failure mode of soft clay ground,a new stability calculation method,considering tension crack of fill,is provided.Meanwhile,it analyzes the relationship of safety factor calculated by new method with lateral deformation and settlement.
On the basis of decadal measurement this paper analyzes the settlement of railway on soft clay ground in Lianyungang.Besides it accurately predicts residual settlement after construction.According to failure mode of soft clay ground,a new stability calculation method,considering tension crack of fill,is provided.Meanwhile,it analyzes the relationship of safety factor calculated by new method with lateral deformation and settlement.
Abstract：
By using the fundamental solutions of circular load applied in the interior of the half space or on the surface of the half space, the second kinds of Fredholm integral equations of pile group in saturated viscoelastic soil are established in the paper. The integral equations can be simplified by means of Laplace transforms methods. By the the numerical solution of the integral equations and the corresponding inverse integral transforms, the displacement, axial force and the shear stress of the piles groups are obtained.
By using the fundamental solutions of circular load applied in the interior of the half space or on the surface of the half space, the second kinds of Fredholm integral equations of pile group in saturated viscoelastic soil are established in the paper. The integral equations can be simplified by means of Laplace transforms methods. By the the numerical solution of the integral equations and the corresponding inverse integral transforms, the displacement, axial force and the shear stress of the piles groups are obtained.
Abstract：
The vibration problem of finite length pile with any variable sections under exciting force is developed,in which the influence of the soil under pile toe and surrounding pile is taken into account.With Laplace transform,the transmit functions of a pile about velocity and displacement are derived.Then,by means of Fourier transform,a quasi analytical solution for the velocity response of pile subjected to a semi sine wave exciting force is developed.Based on the solution,the vibrant properties of pile with sharp reduced or expanded section or continuous variable sections are studied.
The vibration problem of finite length pile with any variable sections under exciting force is developed,in which the influence of the soil under pile toe and surrounding pile is taken into account.With Laplace transform,the transmit functions of a pile about velocity and displacement are derived.Then,by means of Fourier transform,a quasi analytical solution for the velocity response of pile subjected to a semi sine wave exciting force is developed.Based on the solution,the vibrant properties of pile with sharp reduced or expanded section or continuous variable sections are studied.
2000, 22(6): 659-663.
Abstract：
Steady state (SS) strength, an important parameter in evaluating the stability of sand deposits against flow sliding, may be significantly affected by testing details including volume change during saturation and undrained shear, end restraint and non uniform deformation. The error in SS strength due to the volume change can be corrected by using a radial deformation transducer (e.g. HRDT) to measure the radial deformation of a triaxial sample. The effect of end restraint is insignificant for loose sand samples and can be considerably reduced by applying lubricated end platen. The thickness of the lubricant and the membrane should not be too thick to produce additional error in void ratio. A new method is suggested to correct the cross sectional area of a triaxial sample. Reuse of sheared sand material may produce large error in SS strength for sands with high coefficient of uniformity (C u ). The scatter of the void ratio in steady state is about 0.02 for sands with low value of C u , and can be over 0.06 for C u of 2.0～2.7.
Steady state (SS) strength, an important parameter in evaluating the stability of sand deposits against flow sliding, may be significantly affected by testing details including volume change during saturation and undrained shear, end restraint and non uniform deformation. The error in SS strength due to the volume change can be corrected by using a radial deformation transducer (e.g. HRDT) to measure the radial deformation of a triaxial sample. The effect of end restraint is insignificant for loose sand samples and can be considerably reduced by applying lubricated end platen. The thickness of the lubricant and the membrane should not be too thick to produce additional error in void ratio. A new method is suggested to correct the cross sectional area of a triaxial sample. Reuse of sheared sand material may produce large error in SS strength for sands with high coefficient of uniformity (C u ). The scatter of the void ratio in steady state is about 0.02 for sands with low value of C u , and can be over 0.06 for C u of 2.0～2.7.
Abstract：
According to the theory of capillary electrochemical hydrodynamics and electrical double layer , the theoretical model for electrochemical hydrodynamics in water saturated sandy soil and clayey soil are deduced. The coupling relationships among current field,flow field and ion field are developed.
According to the theory of capillary electrochemical hydrodynamics and electrical double layer , the theoretical model for electrochemical hydrodynamics in water saturated sandy soil and clayey soil are deduced. The coupling relationships among current field,flow field and ion field are developed.
Abstract：
This paper, based on statistical analyses of the observed data, dealt with the spatial probabilistic characteristics of shear strength indexes for silty clay in Taiyuan. The statistical data were obtained on the basis of the engineering geologic investigation reports and strength tests in lab .The spatial variability coefficients of the indexes for Taiyuan silty clay were compiled.And also the Beta distribution for strength indexes of Taiyuan silty clay was established. Finally the paper studied the correlation between indexes and got some empirical equations.Besides, the paper studied thoroughly the correlation between the strength indexes of different tests, and the uncertainty of strength test method.
This paper, based on statistical analyses of the observed data, dealt with the spatial probabilistic characteristics of shear strength indexes for silty clay in Taiyuan. The statistical data were obtained on the basis of the engineering geologic investigation reports and strength tests in lab .The spatial variability coefficients of the indexes for Taiyuan silty clay were compiled.And also the Beta distribution for strength indexes of Taiyuan silty clay was established. Finally the paper studied the correlation between indexes and got some empirical equations.Besides, the paper studied thoroughly the correlation between the strength indexes of different tests, and the uncertainty of strength test method.
Abstract：
This paper presents the results of a great deal of tests, which show that the impervious soil materials for the core wall of the dam of “635” water control project are either nondispersive soil or transitional soil. The paper also includes analytical results of the potential dispersive property of the soil materials of the dam through multipleoptional modification tests, these analytical results provide comprehensive and reliable references for use of dispersive soil materials in construction of water control project.
This paper presents the results of a great deal of tests, which show that the impervious soil materials for the core wall of the dam of “635” water control project are either nondispersive soil or transitional soil. The paper also includes analytical results of the potential dispersive property of the soil materials of the dam through multipleoptional modification tests, these analytical results provide comprehensive and reliable references for use of dispersive soil materials in construction of water control project.
Abstract：
In the waste filling, it is extremely important that the earthfill retards the percolation of the waste leached solution. On the basis of a large number of test data, the paper presents the decontamination mechanism and laws of ions frequently appearing in leachate. The results of earthcolumn tests indicate that the structure of layers has effects on the transporting and cleaning of ions in different degree with different ions; that due to exchange of adsorption with bivalent cation (Ca 2+ ,Mg 2+ )in place of monovalent ions the permeability increases 5～10 times; that potential function of typical monovalent ions (NH 4 +,Cl -) is exponential.
In the waste filling, it is extremely important that the earthfill retards the percolation of the waste leached solution. On the basis of a large number of test data, the paper presents the decontamination mechanism and laws of ions frequently appearing in leachate. The results of earthcolumn tests indicate that the structure of layers has effects on the transporting and cleaning of ions in different degree with different ions; that due to exchange of adsorption with bivalent cation (Ca 2+ ,Mg 2+ )in place of monovalent ions the permeability increases 5～10 times; that potential function of typical monovalent ions (NH 4 +,Cl -) is exponential.
Abstract：
In this study,bender elements measuring system was developed on an existing dynamic triaxial apparatus.The measuring technique of determining shear wave velocity in the saturated specimen and its principle are presented.Based on the new measuring system,the elastic shear modulus of the reconstituted specimens are controlled by prestraining to match those in situ with the intention to partly restore the original fabric.Undrained cyclic strain-controlled tests are conducted to analyze the liquefaction potential of the studied soil.The range and mean value of critical shear strain are presented based on the test results,which provides a basis for the evaluation of liquefaction potential.Comparison is also made between the results of the conventional reconstituted specimens and the improved specimens.
In this study,bender elements measuring system was developed on an existing dynamic triaxial apparatus.The measuring technique of determining shear wave velocity in the saturated specimen and its principle are presented.Based on the new measuring system,the elastic shear modulus of the reconstituted specimens are controlled by prestraining to match those in situ with the intention to partly restore the original fabric.Undrained cyclic strain-controlled tests are conducted to analyze the liquefaction potential of the studied soil.The range and mean value of critical shear strain are presented based on the test results,which provides a basis for the evaluation of liquefaction potential.Comparison is also made between the results of the conventional reconstituted specimens and the improved specimens.
Abstract：
The 3DFEM software has been developed for pile foundation. The solid element has been employed to simulate soil and pile,and plate element is used to simulate platform of pile foundation.Penalty element is used to guarantee the harmony of displacement on the nodes which belong to not only solid element but also plate element. The numerical check has proved that the built penalty element is quite effective. On the above base, the software has been employed to analyze the creep settlement, axial stress and friction stress of pile foundation,and some useful conclusions have been drawn.
The 3DFEM software has been developed for pile foundation. The solid element has been employed to simulate soil and pile,and plate element is used to simulate platform of pile foundation.Penalty element is used to guarantee the harmony of displacement on the nodes which belong to not only solid element but also plate element. The numerical check has proved that the built penalty element is quite effective. On the above base, the software has been employed to analyze the creep settlement, axial stress and friction stress of pile foundation,and some useful conclusions have been drawn.
Abstract：
The horizontal limit bearing capacity of bucket foundations and the distribution of the active and passive earth pressure are studied by means of model tests and finite element method. The formula for evaluating the horizontal limit bearing capacity is suggested. Finally, the horizontal bearing capacity of double buckets foundation is investigated and a means to estimte the bearing capacity of the double buckets foundations is given.
The horizontal limit bearing capacity of bucket foundations and the distribution of the active and passive earth pressure are studied by means of model tests and finite element method. The formula for evaluating the horizontal limit bearing capacity is suggested. Finally, the horizontal bearing capacity of double buckets foundation is investigated and a means to estimte the bearing capacity of the double buckets foundations is given.
Abstract：
A newly developed numerical method, RFPA 2D ,used for analysis of rock failure process is applied to study the influence of mesoscopic heterogeneity on macroscopic behavior of rock failure. The failure procedures of rock sample with various kinds of heterogeneity are simulated.The results show that the nonlinear behaviour of rock deformation and fracture pattern are more pronounced in more heterogeneous cases than in homogeneous cases. With increase in the degree of rock homogeneity the macroscopic strength of rock rises following exponent function, macroscopic linearity becomes more obvious,and the macroscopic failure process presents markedly brittle behavior. The numerical tests on 10 samples with same homogeneity index show that the deformation and failure behavior before reaching the maximum strength is nearly the same but varies greatly during the unstable failure process.
A newly developed numerical method, RFPA 2D ,used for analysis of rock failure process is applied to study the influence of mesoscopic heterogeneity on macroscopic behavior of rock failure. The failure procedures of rock sample with various kinds of heterogeneity are simulated.The results show that the nonlinear behaviour of rock deformation and fracture pattern are more pronounced in more heterogeneous cases than in homogeneous cases. With increase in the degree of rock homogeneity the macroscopic strength of rock rises following exponent function, macroscopic linearity becomes more obvious,and the macroscopic failure process presents markedly brittle behavior. The numerical tests on 10 samples with same homogeneity index show that the deformation and failure behavior before reaching the maximum strength is nearly the same but varies greatly during the unstable failure process.
Abstract：
By taking account of the random variability of initial underground stress, seepage and material properties of both rockmass and rockbolt, based upon nonlinear stochastic finite element method, a method of reliability assessment is suggested for the safety of undergound structures. By using the method, the excavation procedure can be simulated step by step. The mean value and standard deviation of displacement and stress of both rockmass and rockbolt can also be conveniently obtained. Applications to a practical engineering project are given to demonstrate the suggested method. Some useful conclusions are also obtained.
By taking account of the random variability of initial underground stress, seepage and material properties of both rockmass and rockbolt, based upon nonlinear stochastic finite element method, a method of reliability assessment is suggested for the safety of undergound structures. By using the method, the excavation procedure can be simulated step by step. The mean value and standard deviation of displacement and stress of both rockmass and rockbolt can also be conveniently obtained. Applications to a practical engineering project are given to demonstrate the suggested method. Some useful conclusions are also obtained.
Abstract：
Based on damage mechanics, the initial damage variable of rock is defined as its ultrasonic velocity, when there is no loading on it. The damage evolution equation was set up by the ultrasonic properties model for rock under loading.The rock strength was predicted by the ultrasonic velocity of rock.
Based on damage mechanics, the initial damage variable of rock is defined as its ultrasonic velocity, when there is no loading on it. The damage evolution equation was set up by the ultrasonic properties model for rock under loading.The rock strength was predicted by the ultrasonic velocity of rock.
Abstract：
The paper presents a foundation parameters identification method under the condition of unknown motion input from the base rock.On the basis of analyzing the motion characteristic of the laminated foundation and using the identification theory of the least-square method,the time domain identification method of the layer foundation parameters is established by solving iteratively the input acceleration value and the layer foundation parameters.In addition,the identification process of the layer foundation parameters is implemented according to test data on the laminated foundation model.The result shows that the method can yields good estimation of the layer foundation parameters.
The paper presents a foundation parameters identification method under the condition of unknown motion input from the base rock.On the basis of analyzing the motion characteristic of the laminated foundation and using the identification theory of the least-square method,the time domain identification method of the layer foundation parameters is established by solving iteratively the input acceleration value and the layer foundation parameters.In addition,the identification process of the layer foundation parameters is implemented according to test data on the laminated foundation model.The result shows that the method can yields good estimation of the layer foundation parameters.
2000, 22(6): 727-730.
Abstract：
Each kind of numerical analysis method in geotechnical engineering has its advantages and limitations. Coupling analysis is often used to model complicated geotechnic problem which involves both continuum and discontinuum. The theory of coupling and the couple method of FEM and DDA are introduced. An example is given to prove the advantages of this couple method.
Each kind of numerical analysis method in geotechnical engineering has its advantages and limitations. Coupling analysis is often used to model complicated geotechnic problem which involves both continuum and discontinuum. The theory of coupling and the couple method of FEM and DDA are introduced. An example is given to prove the advantages of this couple method.
