2007 Vol. 29 No. 3
Abstract：
In the study on geological disposal of high level radioactive nuclear waste,it was important to establish the model of coupled thermo-hydro-mechanical processes and to simulate the laboratory and in-situ tests by numerical methods.Up to now many computation codes for THM coupling analysis had been made up in western countries and Japan.But in China the similar codes developed by Chinese was few.For this reason,through establishing the momentum equilibrium equation,the continuity equation for water,the energy balance equation and the elastoplastic matrix,one coupled thermo-hydro-mechanical model for saturated-unsaturated porous media,in which the swelling pressure could be considered,was suggested,and the relevant two dimensional code of finite element method was developed by the author.Taking the FEBEX in-situ test for geological disposal of high level radioactive nuclear waste as the modeling object,a numerical analysis was carried out.The measured data and the computed values of relative humidity,temperature,total water head and compressive stress in several parts are compared with each other,and some conclusions for the rightness of the code and the analyzed results were obtained.
In the study on geological disposal of high level radioactive nuclear waste,it was important to establish the model of coupled thermo-hydro-mechanical processes and to simulate the laboratory and in-situ tests by numerical methods.Up to now many computation codes for THM coupling analysis had been made up in western countries and Japan.But in China the similar codes developed by Chinese was few.For this reason,through establishing the momentum equilibrium equation,the continuity equation for water,the energy balance equation and the elastoplastic matrix,one coupled thermo-hydro-mechanical model for saturated-unsaturated porous media,in which the swelling pressure could be considered,was suggested,and the relevant two dimensional code of finite element method was developed by the author.Taking the FEBEX in-situ test for geological disposal of high level radioactive nuclear waste as the modeling object,a numerical analysis was carried out.The measured data and the computed values of relative humidity,temperature,total water head and compressive stress in several parts are compared with each other,and some conclusions for the rightness of the code and the analyzed results were obtained.
Abstract：
Using the conformal mapping,the region of exclusion of a hole in a half plane was tansfered into a cirque.Then the analytic functions could be expanded as Laurent seriers in this region.The stresses and displacements under given displacement could be solved by the complex method founded by Muskhelishvili.The influence of the displacements due to different depth and different Poisson’s ratio was discussed,and the influence of the stresses due to different depth was discussed too.It was shown that the exact solutions of the third boundary condition suggested by the author was important in the designing of shield tunnling after the comparision of the solutions under four different conditions with the data observed in five different tunnels.
Using the conformal mapping,the region of exclusion of a hole in a half plane was tansfered into a cirque.Then the analytic functions could be expanded as Laurent seriers in this region.The stresses and displacements under given displacement could be solved by the complex method founded by Muskhelishvili.The influence of the displacements due to different depth and different Poisson’s ratio was discussed,and the influence of the stresses due to different depth was discussed too.It was shown that the exact solutions of the third boundary condition suggested by the author was important in the designing of shield tunnling after the comparision of the solutions under four different conditions with the data observed in five different tunnels.
Abstract：
The extreme conditions of a yield function,which was used as one of the fundamental equations for ultimate analysis of soil mass,together with the equilibrium equation and yield conditions,constituted a complete limit equilibrium problem(a problem of boundary conditions of a load).The velocity field and the velocity equation of the slip surface family may be used to establish a new ultimate analysis method-Generalized Limit Equilibrium Method.An approximate formula for calculating the ultimate load on a foundation was derived by using the generalized limit equilibrium method.The extremum theorem of an ultimate load and the results of calculation proved that if the chosen slip surface(family) came near to the genuine slip surface,the obtained approximate value of an ultimate load was more close to the genuine solution.
The extreme conditions of a yield function,which was used as one of the fundamental equations for ultimate analysis of soil mass,together with the equilibrium equation and yield conditions,constituted a complete limit equilibrium problem(a problem of boundary conditions of a load).The velocity field and the velocity equation of the slip surface family may be used to establish a new ultimate analysis method-Generalized Limit Equilibrium Method.An approximate formula for calculating the ultimate load on a foundation was derived by using the generalized limit equilibrium method.The extremum theorem of an ultimate load and the results of calculation proved that if the chosen slip surface(family) came near to the genuine slip surface,the obtained approximate value of an ultimate load was more close to the genuine solution.
Abstract：
This paper focused on the mechanism of consolidation of warping clay under permeable pressure in the cracks of blanket.Fully considering the non-linear relationships between void ratio and effective stress as well as void ratio and coefficient of permeability,a differential equation with void ratio as a controlting variable was put forward for the large-deformation consolidation.To determine the unknown coefficient(which reflected the variation of initial void ratio,compressibility,permeability.) in the equation,a consolidation test was performed under seepage pressure firstly;and then,numerical method was adopted to solve the equation,so the variation of void ratio during the consolidation was determined.At last,in order to verify the result,both model test(which was designed to simulate the consolidation process of warping clay in the cracks of blanket) and test in-situ(in a reservoir with serious seepage) were carried out.
This paper focused on the mechanism of consolidation of warping clay under permeable pressure in the cracks of blanket.Fully considering the non-linear relationships between void ratio and effective stress as well as void ratio and coefficient of permeability,a differential equation with void ratio as a controlting variable was put forward for the large-deformation consolidation.To determine the unknown coefficient(which reflected the variation of initial void ratio,compressibility,permeability.) in the equation,a consolidation test was performed under seepage pressure firstly;and then,numerical method was adopted to solve the equation,so the variation of void ratio during the consolidation was determined.At last,in order to verify the result,both model test(which was designed to simulate the consolidation process of warping clay in the cracks of blanket) and test in-situ(in a reservoir with serious seepage) were carried out.
Abstract：
Large scale field tests of filling piles were performed in a collapsible loess site with a thickness of 35m under natural content and immersion states.The diameter and length of test piles were 0.8 m and 40 m,respectively.4 types of test piles were designed and several measuring methods were adopted.It was shown by test results that the positive frictional resistance measured from pile ZH2 and the negative frictional resistance measured from pile ZH5 were smaller than those measured from pile ZH3 and pile ZH4;The negative frictional resistance measured from test piles was far greater than the numerical value recommended by ? Code for Building Construction in Collapsible Loess Regions ?(GB50025-2004);The locations of neutral points measured from several pile tests in-situ exceeded the range proposed by ?Technical Code for Building Pile Foundations ?(JGJ 94-94);The collapsible settlement of loess could be decreased with pile group.The results obtained in this paper might be useful for the similar project and to revise GB50025-2004 and Code JGJ 94-94.
Large scale field tests of filling piles were performed in a collapsible loess site with a thickness of 35m under natural content and immersion states.The diameter and length of test piles were 0.8 m and 40 m,respectively.4 types of test piles were designed and several measuring methods were adopted.It was shown by test results that the positive frictional resistance measured from pile ZH2 and the negative frictional resistance measured from pile ZH5 were smaller than those measured from pile ZH3 and pile ZH4;The negative frictional resistance measured from test piles was far greater than the numerical value recommended by ? Code for Building Construction in Collapsible Loess Regions ?(GB50025-2004);The locations of neutral points measured from several pile tests in-situ exceeded the range proposed by ?Technical Code for Building Pile Foundations ?(JGJ 94-94);The collapsible settlement of loess could be decreased with pile group.The results obtained in this paper might be useful for the similar project and to revise GB50025-2004 and Code JGJ 94-94.
Abstract：
Stochastic Medium Model(SMM) was widely used for predicting ground movement induced by tunneling in China.A uniform convergence mode was assumed in this model for the transversal section of tunnel after excavation.According to the observed convergence mode of tunnel,a non-uniform convergence mode was introduced to the SMM method to achieve a better prediction of the ground deformation,and the integral limits for various shapes of cross section,such as the circular,elliptical,rectangular and horse-shoe shaped tunnel were deduced.Based on some case studies,it was found that the uniform convergence assumption cause considerable error for shallow tunnels,so it was important to consider a proper convergence mode to take into account the influence of deformation condition and construction techniques of the tunnel.
Stochastic Medium Model(SMM) was widely used for predicting ground movement induced by tunneling in China.A uniform convergence mode was assumed in this model for the transversal section of tunnel after excavation.According to the observed convergence mode of tunnel,a non-uniform convergence mode was introduced to the SMM method to achieve a better prediction of the ground deformation,and the integral limits for various shapes of cross section,such as the circular,elliptical,rectangular and horse-shoe shaped tunnel were deduced.Based on some case studies,it was found that the uniform convergence assumption cause considerable error for shallow tunnels,so it was important to consider a proper convergence mode to take into account the influence of deformation condition and construction techniques of the tunnel.
Abstract：
The insufficient information of the occurrence condition of earth pressure and the spatial characteristic of soil distribution were two main factors leading to the indeterminacy of the earth pressure acting on rigid retaining wall.In calculation,the former was manifested with the indeterminacy of the calculation model;while the latter was related to the indeterminacy of the mechanical parameters.To the indeterminacy problem of the earth pressure,the more reasonable way was to find some range as the proper estimate of the earth pressure in all possible cases to provide for engineering designer to choose;however,for these two types of problem.i.e.model indeterminacy and parameter indeterminacy,different mathematical methods must be employed to determine the corresponding range of earth pressure.Based on the variational method of limit equilibrium,the functional extreme-value problem of limiting earth pressure was transformed into that of finding the minimum solution of functions with restraints,and the problem of the indeterminacy of earth pressure model due to the nondeterministic wall movement mode was studied.By means of mathematical method of interval analysis,taking the Coulomb formula in case of vertical smooth wall for example,the interval operation and the expansion form of real function were discussed,and the indeterminacy of earth pressure calculation on account of uncertain mechanical parameters was preliminarily analyzed.The methods used in the paper could be applied to study other nondeterministic problems in geotechnical engineering.
The insufficient information of the occurrence condition of earth pressure and the spatial characteristic of soil distribution were two main factors leading to the indeterminacy of the earth pressure acting on rigid retaining wall.In calculation,the former was manifested with the indeterminacy of the calculation model;while the latter was related to the indeterminacy of the mechanical parameters.To the indeterminacy problem of the earth pressure,the more reasonable way was to find some range as the proper estimate of the earth pressure in all possible cases to provide for engineering designer to choose;however,for these two types of problem.i.e.model indeterminacy and parameter indeterminacy,different mathematical methods must be employed to determine the corresponding range of earth pressure.Based on the variational method of limit equilibrium,the functional extreme-value problem of limiting earth pressure was transformed into that of finding the minimum solution of functions with restraints,and the problem of the indeterminacy of earth pressure model due to the nondeterministic wall movement mode was studied.By means of mathematical method of interval analysis,taking the Coulomb formula in case of vertical smooth wall for example,the interval operation and the expansion form of real function were discussed,and the indeterminacy of earth pressure calculation on account of uncertain mechanical parameters was preliminarily analyzed.The methods used in the paper could be applied to study other nondeterministic problems in geotechnical engineering.
Abstract：
Unlike the other road materials,aeolian sand had some compaction characteristics that were key factors of influence on construction qualities of highway in the desert.In order to study the characteristics,a series of laboratory and field tests were performed,which included the experiments of sieve analysis,modified standard compaction,vibrating compaction and field test.By analyzing the sieve analysis test data,it was found that the gradation of aeolian sand was bad,with even fine grains with diameters mostly ranged from 0.25mm to 0.074mm.Then,based on the laboratory compaction test results,a compaction curve was plotted,which was quite different to the other kinds of road materials,and similar to a horizontally-written letter S.There were two peak values in the special curve with the increase of water content,which was the special character of aeolian sand could be well compacted whatever it was dry or wet.Also,according to the laboratory vibrating test results,the best vibrating frequency range was proposed,which was from 45 to 50 Hertz.Moreover,some field compaction tests were carried out.On the construction site of highway,the aeolian sand subgrade was compacted in the condition of natural water content,with optimized construction machines,obtain an acceptable degree of compaction,96%,meeting the current specifications.At last,comparative studies were carried out with electron microscope pictures of aeolian sand,which indicated that the microstructure of compacted dry aeolian sand was much denser than that of natural one.
Unlike the other road materials,aeolian sand had some compaction characteristics that were key factors of influence on construction qualities of highway in the desert.In order to study the characteristics,a series of laboratory and field tests were performed,which included the experiments of sieve analysis,modified standard compaction,vibrating compaction and field test.By analyzing the sieve analysis test data,it was found that the gradation of aeolian sand was bad,with even fine grains with diameters mostly ranged from 0.25mm to 0.074mm.Then,based on the laboratory compaction test results,a compaction curve was plotted,which was quite different to the other kinds of road materials,and similar to a horizontally-written letter S.There were two peak values in the special curve with the increase of water content,which was the special character of aeolian sand could be well compacted whatever it was dry or wet.Also,according to the laboratory vibrating test results,the best vibrating frequency range was proposed,which was from 45 to 50 Hertz.Moreover,some field compaction tests were carried out.On the construction site of highway,the aeolian sand subgrade was compacted in the condition of natural water content,with optimized construction machines,obtain an acceptable degree of compaction,96%,meeting the current specifications.At last,comparative studies were carried out with electron microscope pictures of aeolian sand,which indicated that the microstructure of compacted dry aeolian sand was much denser than that of natural one.
Abstract：
In terms of Biot’s dynamic theory,the multi-polar coordinate and complex function were used to put forward an approximate analysis method for scattering and dynamic stress concentration of steady SV wave around a circular cavity in half space of saturated soil,where a circular cavity with large radius was used to replace the straight boundary of the half space of saturated soil.By using the theory of Helmholtz,the general solution of the Biot’s wave function was given and a system of infinite linear algebraic equations of the problem studied in this paper could be given by means of the complex series expansion technology and the boundary conditions of the solid matrix and the fluid.Then the variation of the coefficient of dynamic stress concentration at boundaries of the cavity was discussed with different parameter conditions.The results of the given example indicated that the method used in this paper was useful and efficient to the scattering and dynamic stress concentration of shear waves in which the straight boundary existed.
In terms of Biot’s dynamic theory,the multi-polar coordinate and complex function were used to put forward an approximate analysis method for scattering and dynamic stress concentration of steady SV wave around a circular cavity in half space of saturated soil,where a circular cavity with large radius was used to replace the straight boundary of the half space of saturated soil.By using the theory of Helmholtz,the general solution of the Biot’s wave function was given and a system of infinite linear algebraic equations of the problem studied in this paper could be given by means of the complex series expansion technology and the boundary conditions of the solid matrix and the fluid.Then the variation of the coefficient of dynamic stress concentration at boundaries of the cavity was discussed with different parameter conditions.The results of the given example indicated that the method used in this paper was useful and efficient to the scattering and dynamic stress concentration of shear waves in which the straight boundary existed.
Abstract：
Previously numerical simulations of deformation and failure of rock specimen using Fast Lagrangian Analysis of Continua(FLAC) were mainly limited to plane strain condition different from the actual test condition of three-dimensional rock specimen in uniaxial compression.In the paper,three-dimensional rock specimen with rough ends was modeled by FLAC-3D.Distribution and evolution of shear strain rate,in-and off-plane displacements in free surfaces were investigated.Evolution of in-and off-plane displacements in vertical symmetrical axis of a free surface was monitored.In elastic stage,the adopted constitutive relation was linear elastic;in strain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off was used and the post-peak constitutive relation was also linear.It was shown that uniform distribution of shear strain rate in free surfaces was changed to non-uniform state prior to peak stress.Symmetrical deformation mode of the specimen was converted into asymmetrical pattern beyond peak stress.Two spatial shear planes were found to be generated within specimen through analysis of the patterns of shear band on four free surfaces.One plane was superior to the others from the viewpoint of area of shear plane.Three-dimensional curved surfaces of in-and off-plane displacements were smooth and flat before losing of symmetry of deformation.Concavo-convex three-dimensional curved surfaces wee observed once the symmetry of deformation was violated.Positions where in-plane displacement changed remarkably corresponded to shear bands.Precursor to deformation and failure of the specimen could be identified form off-plane displacement in vertical symmetrical axis of a free surface since the separation of off-plane displacement-timestep curves occurred prior to peak stress.As timestep increased,three kinds of tendencies of off-plane displacement were observed in strain-softening stage.
Previously numerical simulations of deformation and failure of rock specimen using Fast Lagrangian Analysis of Continua(FLAC) were mainly limited to plane strain condition different from the actual test condition of three-dimensional rock specimen in uniaxial compression.In the paper,three-dimensional rock specimen with rough ends was modeled by FLAC-3D.Distribution and evolution of shear strain rate,in-and off-plane displacements in free surfaces were investigated.Evolution of in-and off-plane displacements in vertical symmetrical axis of a free surface was monitored.In elastic stage,the adopted constitutive relation was linear elastic;in strain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off was used and the post-peak constitutive relation was also linear.It was shown that uniform distribution of shear strain rate in free surfaces was changed to non-uniform state prior to peak stress.Symmetrical deformation mode of the specimen was converted into asymmetrical pattern beyond peak stress.Two spatial shear planes were found to be generated within specimen through analysis of the patterns of shear band on four free surfaces.One plane was superior to the others from the viewpoint of area of shear plane.Three-dimensional curved surfaces of in-and off-plane displacements were smooth and flat before losing of symmetry of deformation.Concavo-convex three-dimensional curved surfaces wee observed once the symmetry of deformation was violated.Positions where in-plane displacement changed remarkably corresponded to shear bands.Precursor to deformation and failure of the specimen could be identified form off-plane displacement in vertical symmetrical axis of a free surface since the separation of off-plane displacement-timestep curves occurred prior to peak stress.As timestep increased,three kinds of tendencies of off-plane displacement were observed in strain-softening stage.
Abstract：
Based on the analysis of composite foundation with hybrid piles in homogeneous soil,the solutions of composite foundation with hybrid piles in layered soil were deduced by introducing elastic layered medium theory,and then a relatively complete theoretical system to analyze composite foundation with hybrid piles in layered soil was built up.Numerical method was used to solve the integral equations,and the axial forces,shear forces and displacements along piles under the actions of cushion were obtained.Comparison with classical elastic solutions verified the accuracy of the presented method and calculating program.Finally,a practical engineering project was studied to illuminate the applicability of the presented method.
Based on the analysis of composite foundation with hybrid piles in homogeneous soil,the solutions of composite foundation with hybrid piles in layered soil were deduced by introducing elastic layered medium theory,and then a relatively complete theoretical system to analyze composite foundation with hybrid piles in layered soil was built up.Numerical method was used to solve the integral equations,and the axial forces,shear forces and displacements along piles under the actions of cushion were obtained.Comparison with classical elastic solutions verified the accuracy of the presented method and calculating program.Finally,a practical engineering project was studied to illuminate the applicability of the presented method.
Abstract：
High strain-rate uniaxial compressive loading tests were produced in the modified split Hopkinson pressure bar(SHPB) with pulse shaper on granite samples.It was shown that the failure of the granite cylinder was typical tensile splitting failure mode by sudden splitting parallel with the direction of uniaxial compressive loading at different strain rates.Besides,it was concluded not only the strength of granite increased,but also the fragment size decreased and fragment numbers increased with the increasing strain rate.To analyze quantitatirely the failure phenomena,the numerical calculation based on a dynamic interacting sliding microcrack model was adopted to investigate the influence of microcracks with the different initial crack length,crack angle,crack space and friction coefficient on the macro-mechanical properties of granite under different strain rates.Accordingly,the strain-dependency of the compression strength and the fragmentation degree of granite was explained reasonably.
High strain-rate uniaxial compressive loading tests were produced in the modified split Hopkinson pressure bar(SHPB) with pulse shaper on granite samples.It was shown that the failure of the granite cylinder was typical tensile splitting failure mode by sudden splitting parallel with the direction of uniaxial compressive loading at different strain rates.Besides,it was concluded not only the strength of granite increased,but also the fragment size decreased and fragment numbers increased with the increasing strain rate.To analyze quantitatirely the failure phenomena,the numerical calculation based on a dynamic interacting sliding microcrack model was adopted to investigate the influence of microcracks with the different initial crack length,crack angle,crack space and friction coefficient on the macro-mechanical properties of granite under different strain rates.Accordingly,the strain-dependency of the compression strength and the fragmentation degree of granite was explained reasonably.
Abstract：
Through the systematic analysis on the monitored data of the soft soil foundation of nearly 20 freeways constructed on the Pearl River Delta,a new method was developed to evaluate the stability of the soft soil foundation by the combination of the monitored data of settlement and deformation characteristics of the soft soil.The stability of the softest soil strata of the foundation could also be analyzed by the new method with the subsurface settlement.
Through the systematic analysis on the monitored data of the soft soil foundation of nearly 20 freeways constructed on the Pearl River Delta,a new method was developed to evaluate the stability of the soft soil foundation by the combination of the monitored data of settlement and deformation characteristics of the soft soil.The stability of the softest soil strata of the foundation could also be analyzed by the new method with the subsurface settlement.
Abstract：
A simple analytical two-stages method for determining the settlement and internal forces of group pile caused by tunneling was present here.The Loganathan analytical solution was used to estimate the free soil settlement induced by tunneling in the first stage.In the second stage,composing the soil movement to the pile,the settlement governing equilibrium equation of single pile was built up based on Winkler model.Then the shielding effect due to pile-pile interaction of passive group pile was computed using integral method.Finally the response of passive group pile due to tunneling was obtained.The obtained result was compared with that from FEM and BEM,and good agreement was obtained.
A simple analytical two-stages method for determining the settlement and internal forces of group pile caused by tunneling was present here.The Loganathan analytical solution was used to estimate the free soil settlement induced by tunneling in the first stage.In the second stage,composing the soil movement to the pile,the settlement governing equilibrium equation of single pile was built up based on Winkler model.Then the shielding effect due to pile-pile interaction of passive group pile was computed using integral method.Finally the response of passive group pile due to tunneling was obtained.The obtained result was compared with that from FEM and BEM,and good agreement was obtained.
Abstract：
A cyclic elasto-plasticity model developed by the authors,which could be used to simulate the large strain development during an entire pre-and post-liquefaction process,had been implemented in an effective stress based and fully coupled finite element program – SWANDYNE II.Three dynamic centrifuge model tests performed in the VELACS project were simulated in this paper using the program.The macroscopic phenomena observed in the physical model tests,such as acceleration series,the generation,diffusion and dissipation of excess pore water pressure,and permanent deformation accumulation,were well reproduced in the numerical models.The calculated stress-strain curves and effective stress paths of typical soil elements in the models were also given by the numerical models,through which the whole liquefaction process of the models could be well understood.
A cyclic elasto-plasticity model developed by the authors,which could be used to simulate the large strain development during an entire pre-and post-liquefaction process,had been implemented in an effective stress based and fully coupled finite element program – SWANDYNE II.Three dynamic centrifuge model tests performed in the VELACS project were simulated in this paper using the program.The macroscopic phenomena observed in the physical model tests,such as acceleration series,the generation,diffusion and dissipation of excess pore water pressure,and permanent deformation accumulation,were well reproduced in the numerical models.The calculated stress-strain curves and effective stress paths of typical soil elements in the models were also given by the numerical models,through which the whole liquefaction process of the models could be well understood.
Abstract：
The relationship of temperature and stress to molecular motion was approved according to the free volume theory in this paper.On the basis of time-temperature superposition,the principle,shift formula and factor of load superposition were represented,which could accelerate creep test of geosynthetics and predict its long term behaviour.The laboratory creep test of geogrid RS50 were analyzed.Smooth primary curves were formed with the help of creep test curves at different load levels through load superposition method.Stress-strain curves at the end of designed life and creep reduction factor of geogrid RS50 are determined,which could be used as reference for engineering design.
The relationship of temperature and stress to molecular motion was approved according to the free volume theory in this paper.On the basis of time-temperature superposition,the principle,shift formula and factor of load superposition were represented,which could accelerate creep test of geosynthetics and predict its long term behaviour.The laboratory creep test of geogrid RS50 were analyzed.Smooth primary curves were formed with the help of creep test curves at different load levels through load superposition method.Stress-strain curves at the end of designed life and creep reduction factor of geogrid RS50 are determined,which could be used as reference for engineering design.
Abstract：
An evaluation of the effectiveness of a selected geomembrane as barrier was necessary.In this study,the chemical resistance of high density polyethylene(HDPE) geomembrane to four organic solvents was investigated using the standard ASTM F-739 and immersion methods.The diffusion of experimental organic solvents in HDPE was non-Fickian kinetic.From the sorption results of immersion test,diffusion coefficients were calculated using Fick’s equation.It was shown by the results of analysis of variance(ANOVA) that the diffusion and solubility coefficients were significantly different(p<0.05) for three thickness of HDPE samples.A good agreement(r2=0.947,p<0.001) of steady state permeation rates was found between ASTM F739 and immersion experiments.The immersion method could be a practical and inexpensive screening test to determine the chemical resistance of HDPE geomembrane.
An evaluation of the effectiveness of a selected geomembrane as barrier was necessary.In this study,the chemical resistance of high density polyethylene(HDPE) geomembrane to four organic solvents was investigated using the standard ASTM F-739 and immersion methods.The diffusion of experimental organic solvents in HDPE was non-Fickian kinetic.From the sorption results of immersion test,diffusion coefficients were calculated using Fick’s equation.It was shown by the results of analysis of variance(ANOVA) that the diffusion and solubility coefficients were significantly different(p<0.05) for three thickness of HDPE samples.A good agreement(r2=0.947,p<0.001) of steady state permeation rates was found between ASTM F739 and immersion experiments.The immersion method could be a practical and inexpensive screening test to determine the chemical resistance of HDPE geomembrane.
Abstract：
Various stochastic factors have mild time-varying negative impact on the flood control safety due to the ageing of hydraulic projects.It is important that the time-varying characteristics of the various stochastic factors are quantitatively predicted to evaluate the time-varying flood control risk rate.A frame to infer the statistical distributions of the stochastic variables is provided by the Bayesian approach.By using the prior information the results of suitable sampling inspections can be used to modify and improve the hypothesis of accumulated statistical distribution to control the time-varying uncertainty.The time-varying characteristics of seepage variable L were analyzed,the feasibility and suitability by using the Bayesian approach to quantitatively predict the time-varying stochastic characteristics were proved.The inspection procedure simulated by using the Normal conjugate function was suggested,and the posterior distribution of L was computed.On this basis,a practical model for quantitatively predicting the seepage risk rate of the embankments and dams was discussed,and the influence of the time-varying characteristics of the stochastic variable L on seepage risk rate was analyzed.
Various stochastic factors have mild time-varying negative impact on the flood control safety due to the ageing of hydraulic projects.It is important that the time-varying characteristics of the various stochastic factors are quantitatively predicted to evaluate the time-varying flood control risk rate.A frame to infer the statistical distributions of the stochastic variables is provided by the Bayesian approach.By using the prior information the results of suitable sampling inspections can be used to modify and improve the hypothesis of accumulated statistical distribution to control the time-varying uncertainty.The time-varying characteristics of seepage variable L were analyzed,the feasibility and suitability by using the Bayesian approach to quantitatively predict the time-varying stochastic characteristics were proved.The inspection procedure simulated by using the Normal conjugate function was suggested,and the posterior distribution of L was computed.On this basis,a practical model for quantitatively predicting the seepage risk rate of the embankments and dams was discussed,and the influence of the time-varying characteristics of the stochastic variable L on seepage risk rate was analyzed.
Abstract：
A new type of ripped-stone embankment proposed by author,was an awning-ripped stone embankment utilizing man-made natural convection of heat transfer as a positive measure for cooling embankment.In this paper,natural convection of heat transfer in ripped-stone layer was described for the heat transfer in large porous media.Numerical tests were implemented to investigate the reasonable value of embankment height,thickness of ripped-stone layer and the particle size of the ripped-stone.The optimizing and designing principle were then suggested: ⑴The new proposed embankment type not only was beneficial to thermal stability of embankment in high temperature areas but also could prevent non-uniform settlement resulted by different temperature between two sides of the embankment and avoid porous filling of the sands by wind.⑵It was suggested that embankment height could be 37 m and thickness of ripped-stone layer be 35 times of partical size of ripped-stone.
A new type of ripped-stone embankment proposed by author,was an awning-ripped stone embankment utilizing man-made natural convection of heat transfer as a positive measure for cooling embankment.In this paper,natural convection of heat transfer in ripped-stone layer was described for the heat transfer in large porous media.Numerical tests were implemented to investigate the reasonable value of embankment height,thickness of ripped-stone layer and the particle size of the ripped-stone.The optimizing and designing principle were then suggested: ⑴The new proposed embankment type not only was beneficial to thermal stability of embankment in high temperature areas but also could prevent non-uniform settlement resulted by different temperature between two sides of the embankment and avoid porous filling of the sands by wind.⑵It was suggested that embankment height could be 37 m and thickness of ripped-stone layer be 35 times of partical size of ripped-stone.
Abstract：
Soil lateral stress σ3 or earth pressure at rest P0 was extensively used in geotechnical engineering designs and calculations.The coefficient of earth pressure at rest k0 were tested with a large number of samples buried above the depth of 500 m in areas,such as Hengshui,Huanghua of Hebei province etc.by using various instruments in different laboratories.It was shown that k0 was not always a constant,it was a variable,indicating the deficiency of the formula K0=△σ3/△σ1 in calculating σ3.This formula was basically applicable to calculate σ3 when the vertical effective stress σ1 was less than 200 kPa in shallow soil,but it was defective when σ1 was larger than 200 kPa,and might cause unsafety and accidence when it was used in deep soil.It was found that there was a good power-law relations between σ3 and σ1 for different soils,and different experimental methods might acquire different results of σ3.Therefore,an improved method was presented to calculate σ3,which could provide reliable data for geotechnical engineering construction and research.
Soil lateral stress σ3 or earth pressure at rest P0 was extensively used in geotechnical engineering designs and calculations.The coefficient of earth pressure at rest k0 were tested with a large number of samples buried above the depth of 500 m in areas,such as Hengshui,Huanghua of Hebei province etc.by using various instruments in different laboratories.It was shown that k0 was not always a constant,it was a variable,indicating the deficiency of the formula K0=△σ3/△σ1 in calculating σ3.This formula was basically applicable to calculate σ3 when the vertical effective stress σ1 was less than 200 kPa in shallow soil,but it was defective when σ1 was larger than 200 kPa,and might cause unsafety and accidence when it was used in deep soil.It was found that there was a good power-law relations between σ3 and σ1 for different soils,and different experimental methods might acquire different results of σ3.Therefore,an improved method was presented to calculate σ3,which could provide reliable data for geotechnical engineering construction and research.
Abstract：
There was significant influence of soil arching on behaviors of piled reinforced embankments.The stress ratio between pile and soil was an important parameter to assess soil arching.Model tests were carried out to investigate the influence of relative displacement between pile and soil,embankment height,width and clear spacing of cap-beam,and geotextile on pile-soil stress ratio and settlements of the embankments.It was shown that: ① Pile-soil stress ratio varied with the relative displacement between pile and soil until some upper and lower bound values.② Higher ratio of embankment height to cap-beam clear spacing as well as higher ratio of cap-beam width to clear spacing would result in higher pile-soil stress ratio.③ The inclusion of geotextile would increase pile-soil stress ratio,the higher the geotextile tensile strength,the higher the stress ratio.④ When the ratio of embankment height to cap-beam clear spacing h/s ≤1.4,apparent differential settlements might occur on the surface of embankment.When h/s ≥1.6,no apparent differential settlements would occur on the surface of embankment.The conclusions drawn from the tests could provide valuable reference for the practice.
There was significant influence of soil arching on behaviors of piled reinforced embankments.The stress ratio between pile and soil was an important parameter to assess soil arching.Model tests were carried out to investigate the influence of relative displacement between pile and soil,embankment height,width and clear spacing of cap-beam,and geotextile on pile-soil stress ratio and settlements of the embankments.It was shown that: ① Pile-soil stress ratio varied with the relative displacement between pile and soil until some upper and lower bound values.② Higher ratio of embankment height to cap-beam clear spacing as well as higher ratio of cap-beam width to clear spacing would result in higher pile-soil stress ratio.③ The inclusion of geotextile would increase pile-soil stress ratio,the higher the geotextile tensile strength,the higher the stress ratio.④ When the ratio of embankment height to cap-beam clear spacing h/s ≤1.4,apparent differential settlements might occur on the surface of embankment.When h/s ≥1.6,no apparent differential settlements would occur on the surface of embankment.The conclusions drawn from the tests could provide valuable reference for the practice.
Abstract：
Dynamic Green’s functions were computed by using an exact dynamic-stiffness matrix method.The interface of foundation and soil was discretized.Based on the displacement boundary conditions at the interface,the dynamic impedances of rigid strip foundation on layered saturated soil were obtained.The dynamic impedances of strip rigid foundation on four different saturated sites(Homogeneous poroelastic half-space,Homogeneous layer with rigid base,A single layer resting on a half-space,Layered saturated soils) were compared and analyzed.The numerical studies indicated the differences between the results of layered site and other sites,and the necessity to use the layered model was shown.When the covering soil was thick,the results of other three sites would be consistent.This method could be extended to calculatie the dynamic impedances of rigid foundations of arbitrary shape embedded in layered poroelastic half-plane.
Dynamic Green’s functions were computed by using an exact dynamic-stiffness matrix method.The interface of foundation and soil was discretized.Based on the displacement boundary conditions at the interface,the dynamic impedances of rigid strip foundation on layered saturated soil were obtained.The dynamic impedances of strip rigid foundation on four different saturated sites(Homogeneous poroelastic half-space,Homogeneous layer with rigid base,A single layer resting on a half-space,Layered saturated soils) were compared and analyzed.The numerical studies indicated the differences between the results of layered site and other sites,and the necessity to use the layered model was shown.When the covering soil was thick,the results of other three sites would be consistent.This method could be extended to calculatie the dynamic impedances of rigid foundations of arbitrary shape embedded in layered poroelastic half-plane.
Abstract：
A finite difference analysis using the computer code FLAC was conducted for a landfill,in order to investigate the tensile stress level of HDPE geotechnical membrane under typical loading conditions in the landfill.The loading conditions considered mere:(1) the deadweight of layer-built waste filled up to 36m;(2) the loads induced by potential differential settlement of base;(3) the dynamic loads caused by earthquake.The main conclusions were that(1) the accumulative tensile stress was developed in HDPE membrane by waste dumping,differential settlement,and earthquake,(2) the remarkable stress in liner HDPE membrane was induced by differential settlement primarily(3) the tensile stress in cover system HDPE membrane was higher than ultimate strength of HDPE geotechnical membrane under motion input with moderate intensity(e.g.peak acceleration was 0.25g).
A finite difference analysis using the computer code FLAC was conducted for a landfill,in order to investigate the tensile stress level of HDPE geotechnical membrane under typical loading conditions in the landfill.The loading conditions considered mere:(1) the deadweight of layer-built waste filled up to 36m;(2) the loads induced by potential differential settlement of base;(3) the dynamic loads caused by earthquake.The main conclusions were that(1) the accumulative tensile stress was developed in HDPE membrane by waste dumping,differential settlement,and earthquake,(2) the remarkable stress in liner HDPE membrane was induced by differential settlement primarily(3) the tensile stress in cover system HDPE membrane was higher than ultimate strength of HDPE geotechnical membrane under motion input with moderate intensity(e.g.peak acceleration was 0.25g).
Abstract：
A new approach for evaluating the permanent displacement of rock mass slope including planar slide and wedge slide during earthquake was presented,which considered deterioration of slide surface during earthquake.The procedure for putting the method into effect was put forward,and three case histories were studied.It was indicated that the approach was available and reasonable to assess the value of the permanent displacement of rock mass slope.The result reached by traditional Newmark method was too small in general.Traditional Newmark method was only suitable to evaluate the rock mass slope with small permanent displacement during earthquake.
A new approach for evaluating the permanent displacement of rock mass slope including planar slide and wedge slide during earthquake was presented,which considered deterioration of slide surface during earthquake.The procedure for putting the method into effect was put forward,and three case histories were studied.It was indicated that the approach was available and reasonable to assess the value of the permanent displacement of rock mass slope.The result reached by traditional Newmark method was too small in general.Traditional Newmark method was only suitable to evaluate the rock mass slope with small permanent displacement during earthquake.
2007, 29(3): 458-462.
Abstract：
Tangent modulus was essential to nonlinear soil model,and it was necessary to understand it properly during numerical simulation.First,a new concept namely half strength index was introduced to build the mathematic properties equations of stress-strain relationship,then the deficiency of hyperbolic expression of the relationship was indicated in terms of it.Second,according to laboratory test data,differential control equation of soil stress-strain relationship was presented and a new 3-parameter stress-strain expression was established.It was shown that the hyperbolic expression was the simplified type of the 3-parameter expression.Third,an improved tangent modulus of soil was obtained based on the new stress-strain expression,and methods to determine its parameters were discussed.Finally,simulation of triaxial test data using the improved tangent modulus was conducted.
Tangent modulus was essential to nonlinear soil model,and it was necessary to understand it properly during numerical simulation.First,a new concept namely half strength index was introduced to build the mathematic properties equations of stress-strain relationship,then the deficiency of hyperbolic expression of the relationship was indicated in terms of it.Second,according to laboratory test data,differential control equation of soil stress-strain relationship was presented and a new 3-parameter stress-strain expression was established.It was shown that the hyperbolic expression was the simplified type of the 3-parameter expression.Third,an improved tangent modulus of soil was obtained based on the new stress-strain expression,and methods to determine its parameters were discussed.Finally,simulation of triaxial test data using the improved tangent modulus was conducted.
Abstract：
The classification of the grade of shrink and expansion for the expansive soils was the initial and essential work for engineering construction in expansive soil area.Based on the principle of Mahalanobis distance discriminant analysis,a classification model of expansive was established in this paper,including five indexes reflecting the shrink and expansion of expansive soil: content of clay grain,content of silt grain,liquid limit,plastic limit and plasticity index,.Linear discriminant functions were obtained through training a large set of expansive samples.It was shown that the classification model of distance discriminant analysis performed excellently with high prediction accuracy and could be used in practical engineering.
The classification of the grade of shrink and expansion for the expansive soils was the initial and essential work for engineering construction in expansive soil area.Based on the principle of Mahalanobis distance discriminant analysis,a classification model of expansive was established in this paper,including five indexes reflecting the shrink and expansion of expansive soil: content of clay grain,content of silt grain,liquid limit,plastic limit and plasticity index,.Linear discriminant functions were obtained through training a large set of expansive samples.It was shown that the classification model of distance discriminant analysis performed excellently with high prediction accuracy and could be used in practical engineering.
Abstract：
Based on the basic assumptions used in the Sarma method,the sliding body was divided into a series of oblique slices and the recursive equation of interslice forces were derived according to the force equilibrium conditions of slices.In consistence with the principle of maximum thrust force,the problem of searching the minimum factor of safety was transformed into that of searching the maximum residual thrust force.By using the dynamic programming,the problem of dividing the oblique slices was transformed into that of multi-stage decision.The procedure and steps of the optimal decision strategy was given based on the recursive equation of thrust force,with which the combination of oblique slices was optimized resulting in the maximum residual thrust force.Since the solution of the Sarma method was the upper-bound in nature,the safety factor thus obtained was the least upper-bound solution of slope stability.It was shown that the optimal combination of oblique slices obtained by the dynamic programming agreed well with the theoretical solution of the mechanics of plasticity,and the factor of safety obtained was slightly bigger than that of the rigorous limit equilibrium method of slices with the vertical slices.
Based on the basic assumptions used in the Sarma method,the sliding body was divided into a series of oblique slices and the recursive equation of interslice forces were derived according to the force equilibrium conditions of slices.In consistence with the principle of maximum thrust force,the problem of searching the minimum factor of safety was transformed into that of searching the maximum residual thrust force.By using the dynamic programming,the problem of dividing the oblique slices was transformed into that of multi-stage decision.The procedure and steps of the optimal decision strategy was given based on the recursive equation of thrust force,with which the combination of oblique slices was optimized resulting in the maximum residual thrust force.Since the solution of the Sarma method was the upper-bound in nature,the safety factor thus obtained was the least upper-bound solution of slope stability.It was shown that the optimal combination of oblique slices obtained by the dynamic programming agreed well with the theoretical solution of the mechanics of plasticity,and the factor of safety obtained was slightly bigger than that of the rigorous limit equilibrium method of slices with the vertical slices.
