2008 Vol. 30 No. 6
Abstract：
A confined compression test was used to investigate the crushing behaviors of coarse quartz sand and fine gravel particles under high compressive stress,and their fractal crushing was studied based on the fractal concept and the measured data of particle-size distribution.It was shown that the quantity of particle breakage increased with the increase of compressive stress and was related to the particle size.With the increase of quantity of particle breakage,the angles of friction increased for coarse sand,increased at first and then decreased for fine gravel.Both had the tendency finally to an unvaried value when the quantity of particle breakage was large enough.It was shown that the particle-size distribution after particle breakage exhibited a statistical fractal feature.The magnitude of fractal crushing dimension reflected the variation of quantity of particle breakage.Large fractal crushing dimension corresponded to large quantity of particle breakage.There was a close relationship between fractal crushing dimension and Hardin index of particle breakage.The relationship between fractal crushing dimension or Hardin’s index and compressive stress could be expressed by hyperbolic curves or semilogarithmic linear curves.As a result,the fractal crushing dimension and Hardin index could be evaluated as long as compressive stress and parameters of soil particles were obtained.The fractal crushing dimension might be useful indicator for quantitative analysis of the particle breakage of granular materials.
A confined compression test was used to investigate the crushing behaviors of coarse quartz sand and fine gravel particles under high compressive stress,and their fractal crushing was studied based on the fractal concept and the measured data of particle-size distribution.It was shown that the quantity of particle breakage increased with the increase of compressive stress and was related to the particle size.With the increase of quantity of particle breakage,the angles of friction increased for coarse sand,increased at first and then decreased for fine gravel.Both had the tendency finally to an unvaried value when the quantity of particle breakage was large enough.It was shown that the particle-size distribution after particle breakage exhibited a statistical fractal feature.The magnitude of fractal crushing dimension reflected the variation of quantity of particle breakage.Large fractal crushing dimension corresponded to large quantity of particle breakage.There was a close relationship between fractal crushing dimension and Hardin index of particle breakage.The relationship between fractal crushing dimension or Hardin’s index and compressive stress could be expressed by hyperbolic curves or semilogarithmic linear curves.As a result,the fractal crushing dimension and Hardin index could be evaluated as long as compressive stress and parameters of soil particles were obtained.The fractal crushing dimension might be useful indicator for quantitative analysis of the particle breakage of granular materials.
Abstract：
A set of stress controlled bi-directional cyclic loading tests under isotropic consolidated condition was conducted for simulating the cyclic stress induced by wave loading.The stress path followed during the test in terms of σ d /2 and τ was controlled in shape of ellipse.The area bounded by the elliptical stress path was kept unchanged while the amplitude of the axial and torsional shear stresses were varied to study the effect of two components on the strength and deformation behavior of saturated loose sand.It was shown that the resistance to liquefaction of saturated sand was considerably related with both the area of elliptical stress path and the ratio of the two stress components.For the same ratio of two stress components,the resistance to liquefaction of saturated sand decreased with the increasing area of the elliptical stress path.However,for the same area of elliptical stress path,the sand might exhibit the highest resistance to liquefaction at a critical ratio of axial and torsional shear stresses,0.60.75.The resistance to liquefaction increased with the increasing ratio of σ d /2 and τ when the ratio was less than the critical value,and decreased with the increasing ratio of σ d /2 and τ when the ratio was larger than the critical value.Moreover,the pore water pressure developed gradually to the initial effective confining pressure with transient fluctuation and phase matching axial load.
A set of stress controlled bi-directional cyclic loading tests under isotropic consolidated condition was conducted for simulating the cyclic stress induced by wave loading.The stress path followed during the test in terms of σ d /2 and τ was controlled in shape of ellipse.The area bounded by the elliptical stress path was kept unchanged while the amplitude of the axial and torsional shear stresses were varied to study the effect of two components on the strength and deformation behavior of saturated loose sand.It was shown that the resistance to liquefaction of saturated sand was considerably related with both the area of elliptical stress path and the ratio of the two stress components.For the same ratio of two stress components,the resistance to liquefaction of saturated sand decreased with the increasing area of the elliptical stress path.However,for the same area of elliptical stress path,the sand might exhibit the highest resistance to liquefaction at a critical ratio of axial and torsional shear stresses,0.60.75.The resistance to liquefaction increased with the increasing ratio of σ d /2 and τ when the ratio was less than the critical value,and decreased with the increasing ratio of σ d /2 and τ when the ratio was larger than the critical value.Moreover,the pore water pressure developed gradually to the initial effective confining pressure with transient fluctuation and phase matching axial load.
Abstract：
Zipingpu Concrete Face Rock-fill Dam was considerably damaged by "5.12" Wenchuan Earthquake.The site investigation showed that the maximum permanent settlement was about 100 cm and the horizontal displacement was about 60 cm as a result of the earthquake.The separation between the concrete face and the cushion layer plane was large in area,the dislocation of the construction joints of the concrete face above the reservoir water level was obvious,and the crushed damage of the vertical joints of the concrete face also occurred because of the permanent displacement due to the earthquake.Based on the field investigation,the damage mechanism was analyzed,and proposals were put forward on the future analytical computation of the earthquake effects on concrete face rock-fill dams,anti-earthquake design and the principle for the rehabilitation of the Zipingpu Concrete Face Rock-fill Dam damaged by the earthquake.
Zipingpu Concrete Face Rock-fill Dam was considerably damaged by "5.12" Wenchuan Earthquake.The site investigation showed that the maximum permanent settlement was about 100 cm and the horizontal displacement was about 60 cm as a result of the earthquake.The separation between the concrete face and the cushion layer plane was large in area,the dislocation of the construction joints of the concrete face above the reservoir water level was obvious,and the crushed damage of the vertical joints of the concrete face also occurred because of the permanent displacement due to the earthquake.Based on the field investigation,the damage mechanism was analyzed,and proposals were put forward on the future analytical computation of the earthquake effects on concrete face rock-fill dams,anti-earthquake design and the principle for the rehabilitation of the Zipingpu Concrete Face Rock-fill Dam damaged by the earthquake.
Abstract：
The fatigue properties of the rock mass with intermittent cracks under blasting and earthquake are the most basic problems in rock mechanics.The force-displacement curves were tested under uni-axial cyclic loading in the experiment and the specimens were made of sandstone-like modeling materials containing two or three pre-existing cracks with different geometry distributions.In virtue of the analysis of irreversible deformation and total deformation with cyclic number,the fatigue deformation properties of the cracked specimens were discussed.Then,some influential factors,such as loading frequency,load level and geometrical position of cracks on fatigue properties of the cracked samples were analyzed and discussed.It was indicated that the development of fatigue deformation of samples with intermittent cracks could be divided the into three stages: the initial deformation stage,the constant deformation rate stage and the accelerative deformation stage which were same as the intact rock and block-jointed rock;the fatigue deformation limit corresponding to the maximum cyclic load was equal to that of post-peak locus of static complete force-displacement curve;and the fatigue deformation was controlled not only by the loading frequency and the load level,but also by the geometrical position of intermittent cracks.
The fatigue properties of the rock mass with intermittent cracks under blasting and earthquake are the most basic problems in rock mechanics.The force-displacement curves were tested under uni-axial cyclic loading in the experiment and the specimens were made of sandstone-like modeling materials containing two or three pre-existing cracks with different geometry distributions.In virtue of the analysis of irreversible deformation and total deformation with cyclic number,the fatigue deformation properties of the cracked specimens were discussed.Then,some influential factors,such as loading frequency,load level and geometrical position of cracks on fatigue properties of the cracked samples were analyzed and discussed.It was indicated that the development of fatigue deformation of samples with intermittent cracks could be divided the into three stages: the initial deformation stage,the constant deformation rate stage and the accelerative deformation stage which were same as the intact rock and block-jointed rock;the fatigue deformation limit corresponding to the maximum cyclic load was equal to that of post-peak locus of static complete force-displacement curve;and the fatigue deformation was controlled not only by the loading frequency and the load level,but also by the geometrical position of intermittent cracks.
Abstract：
The residual deformation behaviors of rock-fill materials were experimentally studied by use of a triaxial apparatus with the medium diameter.The major attention was focused on the influence of the stress level.Based on the test results,the residual deformation model presented by Shen Zhujiang was modified.By use of the modified model,the deformation behaviors of concrete faced rock-fill dams were numerically analyzed.It was shown that the deformation predicted by the modified model was close to that by Shen Zhujiang model for low dams,but with the increase of the dam height and earthquake magnitude,the difference between the two models became larger.
The residual deformation behaviors of rock-fill materials were experimentally studied by use of a triaxial apparatus with the medium diameter.The major attention was focused on the influence of the stress level.Based on the test results,the residual deformation model presented by Shen Zhujiang was modified.By use of the modified model,the deformation behaviors of concrete faced rock-fill dams were numerically analyzed.It was shown that the deformation predicted by the modified model was close to that by Shen Zhujiang model for low dams,but with the increase of the dam height and earthquake magnitude,the difference between the two models became larger.
Abstract：
The textural stress has great effect on the stability of rock.According to the measured geo-stress data,through FEM and combined with the linear multivariate regression method,the geo-stress field was conducted.Based on Yu Maohong’s generalized twin-shear strength theory,the failure type was classified into the generalized tension,the generalized compression the and generalized shear.Using these methods,a diversion tunnel of a large-scale hydropower station was analyzed to study the stress distribution,the peculiarity and process of failure.It was shown that the stress concentration was located at the bottom of the wall and the arch top,the stress in the wall was little and the failure happened at the bottom of the wall and the arch top,then the bottom board and some areas far from the tunnel.Under the condition without considering textural stress,the stress concentration area located in the wall and the failure happened at the bottom of the wall,then in the middle of the wall and at the arch top,the failure elements were concentrat around the tunnel.Based on the deformation observation,the results considering textural stress could reflect the real failure process of tunnels.
The textural stress has great effect on the stability of rock.According to the measured geo-stress data,through FEM and combined with the linear multivariate regression method,the geo-stress field was conducted.Based on Yu Maohong’s generalized twin-shear strength theory,the failure type was classified into the generalized tension,the generalized compression the and generalized shear.Using these methods,a diversion tunnel of a large-scale hydropower station was analyzed to study the stress distribution,the peculiarity and process of failure.It was shown that the stress concentration was located at the bottom of the wall and the arch top,the stress in the wall was little and the failure happened at the bottom of the wall and the arch top,then the bottom board and some areas far from the tunnel.Under the condition without considering textural stress,the stress concentration area located in the wall and the failure happened at the bottom of the wall,then in the middle of the wall and at the arch top,the failure elements were concentrat around the tunnel.Based on the deformation observation,the results considering textural stress could reflect the real failure process of tunnels.
Abstract：
It was shown by the monitored data that uneven deformation would be induced by deep excavation adjacent to one side of the operating subway station.According to the practice of deep excavation adjacent to a subway station in Shanghai,FLAC-3D was employed to establish a numerical model to simulate the deep excavation.The results were in good agreement with the field test data.Effects of relevant construction methods on the deformation of the subway station were analyzed and presented.It was demonstrated by the theoretical results that the application of underpinned piles,revolving-spraying piles and cement-mixed piles in excavation side and partitioning excavation were the effective measures to control the deformation of the operating subway station.The lateral deformation of underground retaining walls would decrease with the increase of depth of reinforcement,but the vertical deformation increased with the increase of depth of reinforcement due to the contact friction force between the retaining walls and the body of reinforcement.
It was shown by the monitored data that uneven deformation would be induced by deep excavation adjacent to one side of the operating subway station.According to the practice of deep excavation adjacent to a subway station in Shanghai,FLAC-3D was employed to establish a numerical model to simulate the deep excavation.The results were in good agreement with the field test data.Effects of relevant construction methods on the deformation of the subway station were analyzed and presented.It was demonstrated by the theoretical results that the application of underpinned piles,revolving-spraying piles and cement-mixed piles in excavation side and partitioning excavation were the effective measures to control the deformation of the operating subway station.The lateral deformation of underground retaining walls would decrease with the increase of depth of reinforcement,but the vertical deformation increased with the increase of depth of reinforcement due to the contact friction force between the retaining walls and the body of reinforcement.
Abstract：
According to the strain path method and source-sink method,the closed-form analytical expressions of displacement fields due to the presence of adjacent piles were obtained.Based on the analytical expressions of singe pile and Lagrange interpolating function,the closed-form analytical expressions of displacement fields of soil around jacked group piles were derived.The solution taking into consideration construction sequence and compacting effects was in accordance with the practical engineering.And the solution could be reduced to simplified solution without consideration of construction sequence and compacting effects.Displacement fields of soil around group piles were analyzed by the solution.It was shown that the displacement of frontal surface was larger and that of dorsal surface was smaller with consideration of construction sequence and compacting effects.
According to the strain path method and source-sink method,the closed-form analytical expressions of displacement fields due to the presence of adjacent piles were obtained.Based on the analytical expressions of singe pile and Lagrange interpolating function,the closed-form analytical expressions of displacement fields of soil around jacked group piles were derived.The solution taking into consideration construction sequence and compacting effects was in accordance with the practical engineering.And the solution could be reduced to simplified solution without consideration of construction sequence and compacting effects.Displacement fields of soil around group piles were analyzed by the solution.It was shown that the displacement of frontal surface was larger and that of dorsal surface was smaller with consideration of construction sequence and compacting effects.
2008, 30(6): 830-834.
Abstract：
For exploring the frequency features of microseismic signals,the frequency spectrum of the signals was obtained with DB5 in 5 levels,and the instantaneous frequency of the signals was achieved with the windowed Fourier transform.Tendency of frequency attenuation was found.High frequency vibrations did occur early in the microseism,and then the frequency was attenuated because of the damping of rock but not by the frequency dispersion of surface waves.The signals were divided into segments and the frequency spectra were got and the frequency features were achieved and 4 types of variation of frequency were found.Half-period of microseismic signals was gained through computing the intervals of adjacent zeros or adjacent peaks of microseismic signals and the tendency of frequency attenuation was found too.The frequency might correlated to the amplitude.Sometimes the larger(smaller) the amplitude,the lower(higher) the period.The relativity of frequency and amplitude might be caused by the nonlinear creep of the rock and it might be a method of studying nonlinear characteristics of rock.
For exploring the frequency features of microseismic signals,the frequency spectrum of the signals was obtained with DB5 in 5 levels,and the instantaneous frequency of the signals was achieved with the windowed Fourier transform.Tendency of frequency attenuation was found.High frequency vibrations did occur early in the microseism,and then the frequency was attenuated because of the damping of rock but not by the frequency dispersion of surface waves.The signals were divided into segments and the frequency spectra were got and the frequency features were achieved and 4 types of variation of frequency were found.Half-period of microseismic signals was gained through computing the intervals of adjacent zeros or adjacent peaks of microseismic signals and the tendency of frequency attenuation was found too.The frequency might correlated to the amplitude.Sometimes the larger(smaller) the amplitude,the lower(higher) the period.The relativity of frequency and amplitude might be caused by the nonlinear creep of the rock and it might be a method of studying nonlinear characteristics of rock.
Abstract：
Air sparging is one of the most efficient techniques to remedy saturated soils and groundwater contaminated with voltaic organic compounds.Based on the model tests,the air flow pattern and the zone of influence(ZOI) were investigated for air sparging process in different types of soil mass.It was shown that the minimum sparging pressure was dependent on the hydro-static pressure and capillary pressure of soil mass;in gravel mass air traveled in bubbles and ZOI was of a parabolic shape;in fine sand mass air flowed in discrete,stable micro-channels and ZOI was larger than those in gravel mass under the same sparging pressure;there was a positive influence of pulsating sparging in sands while it was insignificant in gravels.
Air sparging is one of the most efficient techniques to remedy saturated soils and groundwater contaminated with voltaic organic compounds.Based on the model tests,the air flow pattern and the zone of influence(ZOI) were investigated for air sparging process in different types of soil mass.It was shown that the minimum sparging pressure was dependent on the hydro-static pressure and capillary pressure of soil mass;in gravel mass air traveled in bubbles and ZOI was of a parabolic shape;in fine sand mass air flowed in discrete,stable micro-channels and ZOI was larger than those in gravel mass under the same sparging pressure;there was a positive influence of pulsating sparging in sands while it was insignificant in gravels.
Abstract：
The scattering of P waves by a canyon of arbitrary shape in a fluid-saturated,poroelastic layered half-space was modeled using the indirect boundary element method in the frequency domain.The free-field responses were calculated to determine the displacements and stresses at the surface of the canyon,and fictitious distributed loads were then applied at the surface of the canyon in the free field to calculate the Green’s functions for displacements and stresses.The amplitudes of the fictitious distributed loads were determined from the boundary conditions,and the displacements arising from the waves in the free field and from the fictitious distributed loads were summed to obtain the solution.Numerical results for displacements of saturated layered systems were presented.The results were compared with those of the dry layered site.It was shown that the incident angle,the incident frequency and the parameters of b had great influence on displacements of saturated layered systems.The results of saturated sites were quite different from those of the dry layered site.The rationality and necessity of using the layered model were discussed.
The scattering of P waves by a canyon of arbitrary shape in a fluid-saturated,poroelastic layered half-space was modeled using the indirect boundary element method in the frequency domain.The free-field responses were calculated to determine the displacements and stresses at the surface of the canyon,and fictitious distributed loads were then applied at the surface of the canyon in the free field to calculate the Green’s functions for displacements and stresses.The amplitudes of the fictitious distributed loads were determined from the boundary conditions,and the displacements arising from the waves in the free field and from the fictitious distributed loads were summed to obtain the solution.Numerical results for displacements of saturated layered systems were presented.The results were compared with those of the dry layered site.It was shown that the incident angle,the incident frequency and the parameters of b had great influence on displacements of saturated layered systems.The results of saturated sites were quite different from those of the dry layered site.The rationality and necessity of using the layered model were discussed.
Abstract：
Using the variational principle,an analytical method for the stability analysis of beams on modified Vlasov foundation subjected to lateral loads acting on the ends was developed.The buckling loads and the corresponding mode shapes of the beams could be determined by solving the eigenvalues of the boundary conditions of the beams.It was shown by the parametric study that the effect of the lateral loads acting on the ends was negligible when the height length ratio of the beams was large.Meanwhile,the effect should be considered when the value of the height-length ratio was small.
Using the variational principle,an analytical method for the stability analysis of beams on modified Vlasov foundation subjected to lateral loads acting on the ends was developed.The buckling loads and the corresponding mode shapes of the beams could be determined by solving the eigenvalues of the boundary conditions of the beams.It was shown by the parametric study that the effect of the lateral loads acting on the ends was negligible when the height length ratio of the beams was large.Meanwhile,the effect should be considered when the value of the height-length ratio was small.
Abstract：
In numerical simulation of geotechnical engineering,it is necessary to establish model according to complex engineering geological condition.Modeling is so troublesome that numerical model is often simplified in engineering practice.However,the accuracy and reliability of the calculated results are directly influenced by the characteristics of the model.Thus,the researches on modeling method for numerical analysis are necessary.On the other hand,the 3D geologic model can better reflect the actual geological conditions.With regard to such problem,a new and practical modeling method(CRM Geologic Model Transforming Method) of numerical analysis by combining geologic model and numerical model was presented.This method was implemented using the following procedures: ① cutting the 3D geologic model according to numerical calculation region;② extracting control data from the cut model to reconstruct the model mesh;③ forming the numerical model automatically by the stratum attribute;④ importing the model into numerical analysis system and finishing the modeling work.All procedures were carried out rapidly by programming.In the method,the excavation process could be simulated conveniently and the complex model could be used in different numerical systems.It was proved that the method was more accurate and simple and the efficiency of preprocessor was highly improved.Some useful references would be given by the proposed technology to the continuous researches on this subject.
In numerical simulation of geotechnical engineering,it is necessary to establish model according to complex engineering geological condition.Modeling is so troublesome that numerical model is often simplified in engineering practice.However,the accuracy and reliability of the calculated results are directly influenced by the characteristics of the model.Thus,the researches on modeling method for numerical analysis are necessary.On the other hand,the 3D geologic model can better reflect the actual geological conditions.With regard to such problem,a new and practical modeling method(CRM Geologic Model Transforming Method) of numerical analysis by combining geologic model and numerical model was presented.This method was implemented using the following procedures: ① cutting the 3D geologic model according to numerical calculation region;② extracting control data from the cut model to reconstruct the model mesh;③ forming the numerical model automatically by the stratum attribute;④ importing the model into numerical analysis system and finishing the modeling work.All procedures were carried out rapidly by programming.In the method,the excavation process could be simulated conveniently and the complex model could be used in different numerical systems.It was proved that the method was more accurate and simple and the efficiency of preprocessor was highly improved.Some useful references would be given by the proposed technology to the continuous researches on this subject.
Abstract：
Anisotropic plasticity and structure,together with their evolution laws were considered based on Wheeler’s S-CLAY1 model.The traditional constitutive model was developed to fit for K0 consolidated structured soft clays,consistent with the author’s previous works.The rotational limit line was introduced to the rotational hardening law and a parameter b was added to the model to reflect the evolution of anisotropy.The effect of rotational hardening on the behavior of K0 consolidated structured soft clays was analyzed and the initial value of anisotropic parameter could be obtained from the common laboratory tests.Two typical soft clays,Whenzhou clay and Bothkennar clay,were chosen to be calculated under tiaxial conditions.The importance of the rotational behavior of yield surface was indicated by the comparison of the calculated and tested results.At the same time the method to obtain the parameter b as well as its range was also dicussed.
Anisotropic plasticity and structure,together with their evolution laws were considered based on Wheeler’s S-CLAY1 model.The traditional constitutive model was developed to fit for K0 consolidated structured soft clays,consistent with the author’s previous works.The rotational limit line was introduced to the rotational hardening law and a parameter b was added to the model to reflect the evolution of anisotropy.The effect of rotational hardening on the behavior of K0 consolidated structured soft clays was analyzed and the initial value of anisotropic parameter could be obtained from the common laboratory tests.Two typical soft clays,Whenzhou clay and Bothkennar clay,were chosen to be calculated under tiaxial conditions.The importance of the rotational behavior of yield surface was indicated by the comparison of the calculated and tested results.At the same time the method to obtain the parameter b as well as its range was also dicussed.
Abstract：
Based on the differential equation for curvature of beams,the theory of finite element and the principle of minimum potential energy,a method for beams on Winkler foundation under complex conditions was deduced with compatibility conditions of displacement,angular rotation,moment and shear of adjacent beam elements.The method could be used to compute beams on Winkler foundation under complex conditions,such as variable Young’s modulus and section,complex foundation conditions,namely variable bedding modulus,and complex load consisting of concentrated force,moment and randomly distributed load.The displacement equations both for beam elements and for the whole beam,which had the same structure with the classic solution by Winkler,could be derived from the proposed method.Therefore,the equations for angular rotation,moment and shear of the beams could also be obtained from their differential relationship with displacement equation.It was shown by the computation of an example that the results obtaind by the proposed method were consistent with those by the classic finite element method when the elements were small enough.Furthermore,the element partition in the proposed method was thoroughly different from that in the classic finite element method.
Based on the differential equation for curvature of beams,the theory of finite element and the principle of minimum potential energy,a method for beams on Winkler foundation under complex conditions was deduced with compatibility conditions of displacement,angular rotation,moment and shear of adjacent beam elements.The method could be used to compute beams on Winkler foundation under complex conditions,such as variable Young’s modulus and section,complex foundation conditions,namely variable bedding modulus,and complex load consisting of concentrated force,moment and randomly distributed load.The displacement equations both for beam elements and for the whole beam,which had the same structure with the classic solution by Winkler,could be derived from the proposed method.Therefore,the equations for angular rotation,moment and shear of the beams could also be obtained from their differential relationship with displacement equation.It was shown by the computation of an example that the results obtaind by the proposed method were consistent with those by the classic finite element method when the elements were small enough.Furthermore,the element partition in the proposed method was thoroughly different from that in the classic finite element method.
Abstract：
The purpose of this study was to present the development of an elasto-viscoplastic constitutive model to describe the time-dependent behaviour of soft soils.The elasto-viscoplastic model was established within the framework of Perzyna’s overstress theory and the Modified Cam Clay model.The stress-strain relationship was solved by using an implicit backward Euler method of stress with updated algorithm,and implemented in a finite element program.Different types of tests were simulated using the EVP-MCC model to simulate the time-dependent behaviour of soft soils under different loading conditions,such as the strain rate effects on preconsolidation pressure as well as on undrained shear strength;the primary,secondary consolidation behaviour and stress effects on secondary compression coefficient Cα e;the creep and stress relaxation features under different stress levels.It was shown that the model could satisfactorily describe the time-dependent behaviour of normally consolidated or slightly overconsolidated clayey soils along different loading paths.Time-dependent properties behaved in multiple stages triaxial tests,and field and laboratory pressuremeter tests had also been successfully simualted by the proposed EVP-MCC model.
The purpose of this study was to present the development of an elasto-viscoplastic constitutive model to describe the time-dependent behaviour of soft soils.The elasto-viscoplastic model was established within the framework of Perzyna’s overstress theory and the Modified Cam Clay model.The stress-strain relationship was solved by using an implicit backward Euler method of stress with updated algorithm,and implemented in a finite element program.Different types of tests were simulated using the EVP-MCC model to simulate the time-dependent behaviour of soft soils under different loading conditions,such as the strain rate effects on preconsolidation pressure as well as on undrained shear strength;the primary,secondary consolidation behaviour and stress effects on secondary compression coefficient Cα e;the creep and stress relaxation features under different stress levels.It was shown that the model could satisfactorily describe the time-dependent behaviour of normally consolidated or slightly overconsolidated clayey soils along different loading paths.Time-dependent properties behaved in multiple stages triaxial tests,and field and laboratory pressuremeter tests had also been successfully simualted by the proposed EVP-MCC model.
Abstract：
A new 3D soil-structure interface test apparatus,which was capable of applying monotonic and cyclic loading in three perpendicular directions,was designed and developed to investigate the mechanical characteristics of the interface between coarse grained soil and structure under 3D loading conditions in most practical projects.Monotonic and cyclic tests could be carried out on large section interface sample by this apparatus with high loading capability.Hydraulic servo system was adopted on each loading direction to generate the desired load or displacement paths on the interface.In the normal direction,three boundary conditions including the constant normal stress,the constant volume and the constant normal stiffness could be imposed,while in the two perpendicular tangential directions,numbers of different loading paths,i.e.,cross,circular and elliptical etc.could be imposed.It was shown that this apparatus could be employed to represent the response of the interface under various loading paths.
A new 3D soil-structure interface test apparatus,which was capable of applying monotonic and cyclic loading in three perpendicular directions,was designed and developed to investigate the mechanical characteristics of the interface between coarse grained soil and structure under 3D loading conditions in most practical projects.Monotonic and cyclic tests could be carried out on large section interface sample by this apparatus with high loading capability.Hydraulic servo system was adopted on each loading direction to generate the desired load or displacement paths on the interface.In the normal direction,three boundary conditions including the constant normal stress,the constant volume and the constant normal stiffness could be imposed,while in the two perpendicular tangential directions,numbers of different loading paths,i.e.,cross,circular and elliptical etc.could be imposed.It was shown that this apparatus could be employed to represent the response of the interface under various loading paths.
Abstract：
Through high pressure consolidated tests,the structural yield pressure of loess was obtained by three different methods of data processing,and the structural strength was determined by direct shear tests.Analysis of the relationship between the structural strength and the structural yield pressure,showed that the increment of structural yield pressure was larger than that of the structural strength along with the reducing of moisture content,there was a linear relationship between the increment of the structural strength and the structural yield pressure,and under the coaction of normal stress and horizontal shear stress,the structure of loess was beginning to failure before the normal stress reached the structural yield pressure.
Through high pressure consolidated tests,the structural yield pressure of loess was obtained by three different methods of data processing,and the structural strength was determined by direct shear tests.Analysis of the relationship between the structural strength and the structural yield pressure,showed that the increment of structural yield pressure was larger than that of the structural strength along with the reducing of moisture content,there was a linear relationship between the increment of the structural strength and the structural yield pressure,and under the coaction of normal stress and horizontal shear stress,the structure of loess was beginning to failure before the normal stress reached the structural yield pressure.
Abstract：
K+ and pllyvinyl alcohol were choosen as the inhibition reagent on the hydrating and swelling behavior of expansive soil on the basis of the studies on crystalline swelling and osmosis swelling.Synergistic reaction of K+ and pllyvinyl alcohol which were thought friendly to the environment was proved by a series of tests.It would reduce the free swelling ratio,improve the granularity ingredient and enhance the stability in water.The composition of KCI solution of 7% with pllyvinyl alcohol of 0.6% was regarded as a reasonable proportion.
K+ and pllyvinyl alcohol were choosen as the inhibition reagent on the hydrating and swelling behavior of expansive soil on the basis of the studies on crystalline swelling and osmosis swelling.Synergistic reaction of K+ and pllyvinyl alcohol which were thought friendly to the environment was proved by a series of tests.It would reduce the free swelling ratio,improve the granularity ingredient and enhance the stability in water.The composition of KCI solution of 7% with pllyvinyl alcohol of 0.6% was regarded as a reasonable proportion.
Abstract：
The rockmass around the underground tunnel usually has one suspending side,which may lead to creep under biaxial stress.As time goes by,it may bring serious contraction distortion to the tunnel,namely,creep fracture damage.The experiments were based on the geologic information of Baijiao coal Mine.A 3D structural model was established by use of 3D-σ finite-element software.The heading and bench method was adopted for the tunnel.Then the two-step processing of instability induced by the creep fracture of rockmass was used to analyze the evolution features of the plastic zones caused by the creep fracture.The conclusion might be used to offer theoretical references to the designe of tunnel supports.
The rockmass around the underground tunnel usually has one suspending side,which may lead to creep under biaxial stress.As time goes by,it may bring serious contraction distortion to the tunnel,namely,creep fracture damage.The experiments were based on the geologic information of Baijiao coal Mine.A 3D structural model was established by use of 3D-σ finite-element software.The heading and bench method was adopted for the tunnel.Then the two-step processing of instability induced by the creep fracture of rockmass was used to analyze the evolution features of the plastic zones caused by the creep fracture.The conclusion might be used to offer theoretical references to the designe of tunnel supports.
Abstract：
In order to study the security evaluation and reinforcement option of reinforced bank-protection works on Binjiang road in Yuzhong district of Chongqing,a numerical procedure based on the finite element methods for analysis of behavior of deformations and stresses of reinforced earth structures was presented.In the proposed method,the nonlinear creep behavior of both backfill and geosynthetics used for reinforcements was taken into account by using the rheological models of visco-elasto-plasticity and nonlinear visco-elasticity respectively.Additionally,the interaction effects between the reinforcement and the backfill,the panel and the backfill as well as the panel and the panel were rationally considered.The layer-by-layer filling process of backfill of retaining wall was also simulated.Comparing with the conventional calculation methods and the field measured data,the effectiveness of the method was provend tentatively.Meanwhile,the failure mode,the distribution of tensile stress in reinforcing materials and the safety index in high reinforced retaining walls were obtained.
In order to study the security evaluation and reinforcement option of reinforced bank-protection works on Binjiang road in Yuzhong district of Chongqing,a numerical procedure based on the finite element methods for analysis of behavior of deformations and stresses of reinforced earth structures was presented.In the proposed method,the nonlinear creep behavior of both backfill and geosynthetics used for reinforcements was taken into account by using the rheological models of visco-elasto-plasticity and nonlinear visco-elasticity respectively.Additionally,the interaction effects between the reinforcement and the backfill,the panel and the backfill as well as the panel and the panel were rationally considered.The layer-by-layer filling process of backfill of retaining wall was also simulated.Comparing with the conventional calculation methods and the field measured data,the effectiveness of the method was provend tentatively.Meanwhile,the failure mode,the distribution of tensile stress in reinforcing materials and the safety index in high reinforced retaining walls were obtained.
Abstract：
A dynamic numerical simulation model of soil slopes was established with FLAC3D program,and the validity of simulation was validated with a shaking table model test.Based on this,the dynamic response laws and the influence of parameters of ground motion on the responses under earthquakes were analyzed.It was shown that the input seismic waves were affected by vertical and surface amplification of the slopes,and the effect amplified the input seismic waves with low frequency and filtered those with high frequency.It was reported that the coefficients of amplification of PGA along the slope surface decreased with the increase of amplitudes and frequencies of earthquakes,while these coefficients were less affected by the duration.It was also indicated that the maximum displacement of the slopes evidently increased with increase of amplitudes and duration of earthquakes while decreased with increase of frequencies.Furthermore,it was shown by the location and the shape of the maximum shear-strain increment region that the failure pattern of homogeneous soil slopes under earthquakes is instability along a potential sliding surface,similar to that under static condition.The results were helpful to further researches on the mechanism of slope instability under earthquakes.
A dynamic numerical simulation model of soil slopes was established with FLAC3D program,and the validity of simulation was validated with a shaking table model test.Based on this,the dynamic response laws and the influence of parameters of ground motion on the responses under earthquakes were analyzed.It was shown that the input seismic waves were affected by vertical and surface amplification of the slopes,and the effect amplified the input seismic waves with low frequency and filtered those with high frequency.It was reported that the coefficients of amplification of PGA along the slope surface decreased with the increase of amplitudes and frequencies of earthquakes,while these coefficients were less affected by the duration.It was also indicated that the maximum displacement of the slopes evidently increased with increase of amplitudes and duration of earthquakes while decreased with increase of frequencies.Furthermore,it was shown by the location and the shape of the maximum shear-strain increment region that the failure pattern of homogeneous soil slopes under earthquakes is instability along a potential sliding surface,similar to that under static condition.The results were helpful to further researches on the mechanism of slope instability under earthquakes.
Abstract：
When waves propagate over a porous sea bed,the strength of soils in seabed will vary non-uniformly with depth.On the basis of Biot’s consolidation theory,the distributions of the volume strain of soils along the depth was discussed considering of influences of permeability,shear modulus,wave period,water depth and soil thickness.It was shown that under the action of waves,there’s a hard layer at the depth of 0.12 wavelength in silty seabed of infinite thickness;the wave-induced hard layer was at the surface of seabed when the thickness of sediment was less than half a wavelength;when the thickness was larger than half a wavelength,the wave-induced hard layer was at a depth increasing as seabed thickness increases;the wave-induced strength of soils was apparently non-uniform under the influence of shear modulus and permeability of soil,wave period and water depth.
When waves propagate over a porous sea bed,the strength of soils in seabed will vary non-uniformly with depth.On the basis of Biot’s consolidation theory,the distributions of the volume strain of soils along the depth was discussed considering of influences of permeability,shear modulus,wave period,water depth and soil thickness.It was shown that under the action of waves,there’s a hard layer at the depth of 0.12 wavelength in silty seabed of infinite thickness;the wave-induced hard layer was at the surface of seabed when the thickness of sediment was less than half a wavelength;when the thickness was larger than half a wavelength,the wave-induced hard layer was at a depth increasing as seabed thickness increases;the wave-induced strength of soils was apparently non-uniform under the influence of shear modulus and permeability of soil,wave period and water depth.
Abstract：
An effective approach for formulating the initial geostress field was presented based on the ideas of sub-model method.Firstly,considering mainly the topographical influences of the nearby engineering projects,a large-scale monolithic model was created,and the geostress field was back analyzed initially with the neural network method.Then,considering influences of some main geological structures,the refined sub-model was created,and the more precise initial geostress field of the sub-model was obtained by finite element analysis iteration with interpolated displacement boundary conditions.Finally,the back analysis on the initial geostress filed of the left bank region for Xiluodu Hydropower Project was adopted to verify the described method.It was shown that the complication of problems was reduced by this approach and the more accurate initial geostress field could be obtained efficiently as a foundation for the engineering design and construction.
An effective approach for formulating the initial geostress field was presented based on the ideas of sub-model method.Firstly,considering mainly the topographical influences of the nearby engineering projects,a large-scale monolithic model was created,and the geostress field was back analyzed initially with the neural network method.Then,considering influences of some main geological structures,the refined sub-model was created,and the more precise initial geostress field of the sub-model was obtained by finite element analysis iteration with interpolated displacement boundary conditions.Finally,the back analysis on the initial geostress filed of the left bank region for Xiluodu Hydropower Project was adopted to verify the described method.It was shown that the complication of problems was reduced by this approach and the more accurate initial geostress field could be obtained efficiently as a foundation for the engineering design and construction.
Abstract：
Based on the unloading experiments and according to the extreme depth affected by unloading in the direct shear tests,the strong rebound depth in the conventional consolidation tests and the large depth with varying lateral pressures in K0 consolidation tests,the proper stabilization depth of soil in passive area of foundation pits was put forward,and was verified through calculation and engineering practice.The obtained results were valuable to the reference for engineering design of stabilization affected by unloading.
Based on the unloading experiments and according to the extreme depth affected by unloading in the direct shear tests,the strong rebound depth in the conventional consolidation tests and the large depth with varying lateral pressures in K0 consolidation tests,the proper stabilization depth of soil in passive area of foundation pits was put forward,and was verified through calculation and engineering practice.The obtained results were valuable to the reference for engineering design of stabilization affected by unloading.
Abstract：
The evaluation of stability of surrounding rock is a complicated uncertainty system problem.Based on the set pair analysis(SPA) and the variable fuzzy sets theory,a new fuzzy comprehensive classification model was established.In order to simplify the evaluation procedure and improve the accuracy and reliability of results,a new method to construct relative difference degree was proposed.Moreover,it was shown by comparison of results between a practical example and other methods that the proposed method used to evaluate the stability of surrounding rock was feasible and effective,and more objective.
The evaluation of stability of surrounding rock is a complicated uncertainty system problem.Based on the set pair analysis(SPA) and the variable fuzzy sets theory,a new fuzzy comprehensive classification model was established.In order to simplify the evaluation procedure and improve the accuracy and reliability of results,a new method to construct relative difference degree was proposed.Moreover,it was shown by comparison of results between a practical example and other methods that the proposed method used to evaluate the stability of surrounding rock was feasible and effective,and more objective.
Abstract：
Based on the three-dimensional finite element method(3D FEM),the behavior of super-long two-pile foundation in homogeneous soil was investigated.During the course of establishing the finite element model,both the piles and soil were simulated using 8-node isoparametric elements in order to consider the co-action of the piles and soil,and a layer of thin element was placed along the side surface of the piles in order to consider the possible nonlinear deformation between the piles and soil.The relationship between stress and strain of concrete around the piles was simulated using a linear elastic model,that of the foundation soil was simulated using a nonlinear elastic model suggested by Duncan & Chang,and that of the special thin element was simulated by a special model suggested by Hohai University of China.The computed results indicated that the vertical stiffness of the piles in the super-long two-pile foundation increased with the increase of the distance between the two piles or the length of the piles,but the stiffness was always less than that of single super-long pile.The coefficient of two-pile foundation effect defined by the combination of critical tip resistance and side resistance of the piles was also investigated.The coefficient increased with the increase of the settlement at pile top or the distance between the two piles.But with the increase of the pile length,the coefficient first decreased and then increased or was almost invariant.
Based on the three-dimensional finite element method(3D FEM),the behavior of super-long two-pile foundation in homogeneous soil was investigated.During the course of establishing the finite element model,both the piles and soil were simulated using 8-node isoparametric elements in order to consider the co-action of the piles and soil,and a layer of thin element was placed along the side surface of the piles in order to consider the possible nonlinear deformation between the piles and soil.The relationship between stress and strain of concrete around the piles was simulated using a linear elastic model,that of the foundation soil was simulated using a nonlinear elastic model suggested by Duncan & Chang,and that of the special thin element was simulated by a special model suggested by Hohai University of China.The computed results indicated that the vertical stiffness of the piles in the super-long two-pile foundation increased with the increase of the distance between the two piles or the length of the piles,but the stiffness was always less than that of single super-long pile.The coefficient of two-pile foundation effect defined by the combination of critical tip resistance and side resistance of the piles was also investigated.The coefficient increased with the increase of the settlement at pile top or the distance between the two piles.But with the increase of the pile length,the coefficient first decreased and then increased or was almost invariant.
