2008 Vol. 30 No. 5
Abstract：
Soil reinforced with horizontal-vertical(H-V) inclusions orthogonally is a new concept of reinforced soil.In the H-V reinforced soil,besides the conventional horizontal inclusions,vertical reinforced elements are also placed on the horizontal ones.A series of laboratory triaxial compression tests on sand specimens reinforced with H-V orthogonal inclusions were carried out.Particle flow code(PFC),based on the discrete element method(DEM),was introduced to simulate the triaxial tests.The macro stress-strain relation of the sand specimens reinforced with H-V inclusions was reproduced and verified by PFC2D model,and the fundamental mechanism was also analyzed.From the numerical simulation of PFC2D,the occurrence and propagation of shear band were studied and some useful conclusions were drawn.
Soil reinforced with horizontal-vertical(H-V) inclusions orthogonally is a new concept of reinforced soil.In the H-V reinforced soil,besides the conventional horizontal inclusions,vertical reinforced elements are also placed on the horizontal ones.A series of laboratory triaxial compression tests on sand specimens reinforced with H-V orthogonal inclusions were carried out.Particle flow code(PFC),based on the discrete element method(DEM),was introduced to simulate the triaxial tests.The macro stress-strain relation of the sand specimens reinforced with H-V inclusions was reproduced and verified by PFC2D model,and the fundamental mechanism was also analyzed.From the numerical simulation of PFC2D,the occurrence and propagation of shear band were studied and some useful conclusions were drawn.
Abstract：
Based on the surrounding pressure,shrinkage of whole body,strong deformation characteristics of soft rock in deep roadways,a stress-relief method of active control was established.It was put forward that the expansive deformation energy of surrounding rock would be released,the high stress be transferred to the deeper surrounding rock,and the stress in shallow rock be reduced.Considering the geological conditions of the west tunnel in Guhanshan Mine,the rational space for deformation release was determined.Using high-water rapid hardening materials to reinforce the mudstone easily weakened and expanded by water,the rational time of the secondary support was obtained.The obtained results were successfully applied in the coal mining,and the large deformation of soft rock in deep roadways could be controlled effectively.
Based on the surrounding pressure,shrinkage of whole body,strong deformation characteristics of soft rock in deep roadways,a stress-relief method of active control was established.It was put forward that the expansive deformation energy of surrounding rock would be released,the high stress be transferred to the deeper surrounding rock,and the stress in shallow rock be reduced.Considering the geological conditions of the west tunnel in Guhanshan Mine,the rational space for deformation release was determined.Using high-water rapid hardening materials to reinforce the mudstone easily weakened and expanded by water,the rational time of the secondary support was obtained.The obtained results were successfully applied in the coal mining,and the large deformation of soft rock in deep roadways could be controlled effectively.
Abstract：
A new type of piled raft was developed with the gap between pile top and raft.It could be adopted to adjust the raft-pile-soil interaction and to reduce differential settlement of buildings.Model tests on piled raft in sand with and without the gap between pile top and raft were carried out.It was shown that the sand among piles with the gap between pile top and raft was compacted earlier than that of coventional piled raft foundation under the same load.The compaction of sand among piles could increase the load carried by soil and at the same time reduce the penetration of pile tip.This would make piles and soil settle together.Piled raft with the gap between pile top and raft could mobilize the bearing capacity of soil effectively,in the meantime reduce the stress concentration at pile top and enhance the bearing resistance of pile tip.
A new type of piled raft was developed with the gap between pile top and raft.It could be adopted to adjust the raft-pile-soil interaction and to reduce differential settlement of buildings.Model tests on piled raft in sand with and without the gap between pile top and raft were carried out.It was shown that the sand among piles with the gap between pile top and raft was compacted earlier than that of coventional piled raft foundation under the same load.The compaction of sand among piles could increase the load carried by soil and at the same time reduce the penetration of pile tip.This would make piles and soil settle together.Piled raft with the gap between pile top and raft could mobilize the bearing capacity of soil effectively,in the meantime reduce the stress concentration at pile top and enhance the bearing resistance of pile tip.
Abstract：
Based on the analysis of the geology of levee foundation and hydrologic geology,in order to understand the reason of seepage failure occurred in the levee foundation,the complex levee foundation was divided into three kinds,and the simulation experiments were performed.The failure characteristics and influencing factors of seepage were studied for uniform sand foundation in laboratory.It was found that seepage filure of uniform sand foundation mainly occurred in the contact zone of levee and levee foundation,and the failure hydraulic gradient was dependent on the failure hydraulic gradient of sand seam.When there was declutch problem,the failure hydraulic gradient became the washing hydraulic gradient on surface of sand seam.
Based on the analysis of the geology of levee foundation and hydrologic geology,in order to understand the reason of seepage failure occurred in the levee foundation,the complex levee foundation was divided into three kinds,and the simulation experiments were performed.The failure characteristics and influencing factors of seepage were studied for uniform sand foundation in laboratory.It was found that seepage filure of uniform sand foundation mainly occurred in the contact zone of levee and levee foundation,and the failure hydraulic gradient was dependent on the failure hydraulic gradient of sand seam.When there was declutch problem,the failure hydraulic gradient became the washing hydraulic gradient on surface of sand seam.
Abstract：
For numerous constitutive models are established based on the coaxial theory and validated only under triaxial compression condition,the soil behavior is inaccurately described under the true triaxial condition.A 3D non-coaxial elasto-plasticity model with a novel su?rface shape was proposed to simulate stress-strain curves before bifurcation and to predict the bifurcation strength.It was shown that both the pre-bifurcation deformation and the bifurcation strength were strongly affected by the intermediate principal stress,and the peak failure stemmed from the onset of strain localization when the ratio of intermediate principal stress was beyond 0.2.It was shown by comparisons between the predicted and experimental results on dense sands that the 3D non-coaxial model was more reasonable to be used to predict the bifurcation strength than the coaxial one under the true triaxial condition.
For numerous constitutive models are established based on the coaxial theory and validated only under triaxial compression condition,the soil behavior is inaccurately described under the true triaxial condition.A 3D non-coaxial elasto-plasticity model with a novel su?rface shape was proposed to simulate stress-strain curves before bifurcation and to predict the bifurcation strength.It was shown that both the pre-bifurcation deformation and the bifurcation strength were strongly affected by the intermediate principal stress,and the peak failure stemmed from the onset of strain localization when the ratio of intermediate principal stress was beyond 0.2.It was shown by comparisons between the predicted and experimental results on dense sands that the 3D non-coaxial model was more reasonable to be used to predict the bifurcation strength than the coaxial one under the true triaxial condition.
Abstract：
Heat transfer equation is a kind of basic mathematical-physical equation.The thermal diffusivity is an important thermal physical parameter for soil.The derivation was presented for the one-dimensional heat tranfer equation by means of Fourier series.With the assumption of wave equation for ground temperature,the analytical solution for the distribution of ground temperature at different depths was presented.Based on the analytical solution of heat transfer equation,the principle of measured soil moisture by means of thermal diffusivity was discussed,and two kinds of methods were forward put to evaluate the soil thermal diffusivity,i.e.,the amplitude method and the phase method.The principle of numerical methods to simulate heat transfer in soil was also discussed.Finally,these methods were verified by examples.
Heat transfer equation is a kind of basic mathematical-physical equation.The thermal diffusivity is an important thermal physical parameter for soil.The derivation was presented for the one-dimensional heat tranfer equation by means of Fourier series.With the assumption of wave equation for ground temperature,the analytical solution for the distribution of ground temperature at different depths was presented.Based on the analytical solution of heat transfer equation,the principle of measured soil moisture by means of thermal diffusivity was discussed,and two kinds of methods were forward put to evaluate the soil thermal diffusivity,i.e.,the amplitude method and the phase method.The principle of numerical methods to simulate heat transfer in soil was also discussed.Finally,these methods were verified by examples.
Abstract：
The measurement and analysis of pore water pressure is significant for the studies on under watervacuum preloading method.In order to study the variation of pore water pressure,the full-scale field tests were performed.It was indicated that the variation of pore water pressure was influenced by water pressures on the sealing membrane and negative pressures in sand cushion.The variation of stress in soil was equal to the difference between the values of pore pressure before and during vacuum preloading,indicating that water pressures on the sealing membrane could act as preloading loads.When the depth of water on membrane increased,the positive pore pressure would be induced in soil which,and it similar to the surcharge load.The distribution of negative pore pressure in soil was not uniform,causing differential settlement and strength increase.
The measurement and analysis of pore water pressure is significant for the studies on under watervacuum preloading method.In order to study the variation of pore water pressure,the full-scale field tests were performed.It was indicated that the variation of pore water pressure was influenced by water pressures on the sealing membrane and negative pressures in sand cushion.The variation of stress in soil was equal to the difference between the values of pore pressure before and during vacuum preloading,indicating that water pressures on the sealing membrane could act as preloading loads.When the depth of water on membrane increased,the positive pore pressure would be induced in soil which,and it similar to the surcharge load.The distribution of negative pore pressure in soil was not uniform,causing differential settlement and strength increase.
Abstract：
The non-linear coupling classification technique of surrounding rock mass was put forward based on the rock engineering system,considering the combined action of influential factors and paying attention to the variation of engineering state.All the influential factors and in-site sample values were firstly searched,then the nerve net was applied to establish coupling effect matrix.The stability classification index was put forward,and the scopes of stability parameters were obtained by the regress statistic analysis of the main influential factors and mechanism of action.It was indicated that,when the rock mass was in five stability states of worst instability,instability,stability,more stability,best stability,then five corresponding scopes of Sp were 0～0.24,0.24～0.46,0.46～0.72,0.72～1.15,>1.15,respectively.Through analysis of the main factors,intact rock strength,rock mass structure,RQD value,and supporting method were taken for the four most beneficial factors to rock mass stability of Jinchuan Mine.But the exploitation depth,groundwater permeability,open degree of structure face,and relation of engineering alignment and discontinuity occurrence were taken for the four worst factors.It was indicated by the application of 1120 m-roadway engineering in Jinchuan Mine that the stability state of surrounding rock mass could be inspected by this technique dynamically to provide duly reliable theoretical basis for the supporting design.
The non-linear coupling classification technique of surrounding rock mass was put forward based on the rock engineering system,considering the combined action of influential factors and paying attention to the variation of engineering state.All the influential factors and in-site sample values were firstly searched,then the nerve net was applied to establish coupling effect matrix.The stability classification index was put forward,and the scopes of stability parameters were obtained by the regress statistic analysis of the main influential factors and mechanism of action.It was indicated that,when the rock mass was in five stability states of worst instability,instability,stability,more stability,best stability,then five corresponding scopes of Sp were 0～0.24,0.24～0.46,0.46～0.72,0.72～1.15,>1.15,respectively.Through analysis of the main factors,intact rock strength,rock mass structure,RQD value,and supporting method were taken for the four most beneficial factors to rock mass stability of Jinchuan Mine.But the exploitation depth,groundwater permeability,open degree of structure face,and relation of engineering alignment and discontinuity occurrence were taken for the four worst factors.It was indicated by the application of 1120 m-roadway engineering in Jinchuan Mine that the stability state of surrounding rock mass could be inspected by this technique dynamically to provide duly reliable theoretical basis for the supporting design.
Abstract：
According to large quantity of data obtained from the ground GPS monitoring and underground investigation,the current status of the ground movement,deformation and fracture induced by underground backfill mining in Jinchuan Mine No.2 was given.Based on the detailed analysis of its development process,the main reason and mechanism of the ground movement,deformation and fracture lagged behind the backfill mining were studied,and the intense aftereffect was analyzed and the formation mechanism was also given.At the same time,the mechanism was well studied in the respect of space development process,indicating the relationship between the rock mass movement,deformation,fracture and the whole mine during the period of cut-and-fill.The obtained conclusion was consistent with that obtained in situ and might be used to guide the future production.
According to large quantity of data obtained from the ground GPS monitoring and underground investigation,the current status of the ground movement,deformation and fracture induced by underground backfill mining in Jinchuan Mine No.2 was given.Based on the detailed analysis of its development process,the main reason and mechanism of the ground movement,deformation and fracture lagged behind the backfill mining were studied,and the intense aftereffect was analyzed and the formation mechanism was also given.At the same time,the mechanism was well studied in the respect of space development process,indicating the relationship between the rock mass movement,deformation,fracture and the whole mine during the period of cut-and-fill.The obtained conclusion was consistent with that obtained in situ and might be used to guide the future production.
Abstract：
The line sink drainage element method was proposed to solve the problem that small FEM grid was needed near drainage holes due to the high hydraulic gradient at the cost of time consuming.Based on the assumption that the water flow around the drainage holes was radial one,the flux of the drainage holes was determined.Then,the line sink drainage elements were created by establishing the relationship between the drainage flux and water heads of the nodes of conventional element containing the drainage holes.The differences among the line sink drainage elements used in completely penetrating single well,well cluster,and partially penetrating well were discussed,and the conclusion was drawn that replacing well cluster and partially penetrating well with completely penetrating single well only brought small error.The line sink drainage elements could be used to simulate the function of drainage holes in a simple way with high precision.
The line sink drainage element method was proposed to solve the problem that small FEM grid was needed near drainage holes due to the high hydraulic gradient at the cost of time consuming.Based on the assumption that the water flow around the drainage holes was radial one,the flux of the drainage holes was determined.Then,the line sink drainage elements were created by establishing the relationship between the drainage flux and water heads of the nodes of conventional element containing the drainage holes.The differences among the line sink drainage elements used in completely penetrating single well,well cluster,and partially penetrating well were discussed,and the conclusion was drawn that replacing well cluster and partially penetrating well with completely penetrating single well only brought small error.The line sink drainage elements could be used to simulate the function of drainage holes in a simple way with high precision.
Abstract：
Model tests were carried out in laboratory to get the relationship between the vertical load and the horizontal soil pressure in the surface of soft mucky soil.The thickness of the crust overlying soft mucky soil was less than one fourth of the width of the loaded area.Being limited by the current experimental ability,the horizontal and vertical stresses of one point in ground couldn’t be measured at once.It was the difficulty for the further analysis of the closure effect.PFC software was used to establish mechanical model for the analysis of stress distribution in soft soil during the elastic stage considering the closure effect.Based on the analysis of stress distribution in soft soil during the elastic stage,the stress path method was used to clarify how the critical edge pressure of the two-layered ground was affected by the closure effect.Then it was concluded that K0 in the surface of the soft mucky soil was increased due to the closure effect,so that the development of plastic state of the soft clay was delayed,and the critical edge load of two-layered ground was increased.
Model tests were carried out in laboratory to get the relationship between the vertical load and the horizontal soil pressure in the surface of soft mucky soil.The thickness of the crust overlying soft mucky soil was less than one fourth of the width of the loaded area.Being limited by the current experimental ability,the horizontal and vertical stresses of one point in ground couldn’t be measured at once.It was the difficulty for the further analysis of the closure effect.PFC software was used to establish mechanical model for the analysis of stress distribution in soft soil during the elastic stage considering the closure effect.Based on the analysis of stress distribution in soft soil during the elastic stage,the stress path method was used to clarify how the critical edge pressure of the two-layered ground was affected by the closure effect.Then it was concluded that K0 in the surface of the soft mucky soil was increased due to the closure effect,so that the development of plastic state of the soft clay was delayed,and the critical edge load of two-layered ground was increased.
Abstract：
Based on a practical project of Wushaoling tunnel,a squeezing ground tunnel with high geostress conditions,the essential characteristics of squeezing ground tunnels were analyzed according to the monitored data.In terms of laboratory tests and in-situ monitoring,the physical and mechanical parameters of surrounding rock were synthetically established and analyzed.The condition for the generation of plastic zone arround tunnels,the influencing factors of plastic zone and displacement of tunnels and the relationship between radius of plastic zone and displacement of tunnel were quantitatively analyzed.Based on the monitored data,theoretical calculation and experience of similar tunnels,considering relative deformation,strength stress ratio,ground stress,elastic ratio and comprehensive coefficient α as classification indexes,the classification criterion and measures to prevent large deformation of squeezing ground tunnels were worked out.
Based on a practical project of Wushaoling tunnel,a squeezing ground tunnel with high geostress conditions,the essential characteristics of squeezing ground tunnels were analyzed according to the monitored data.In terms of laboratory tests and in-situ monitoring,the physical and mechanical parameters of surrounding rock were synthetically established and analyzed.The condition for the generation of plastic zone arround tunnels,the influencing factors of plastic zone and displacement of tunnels and the relationship between radius of plastic zone and displacement of tunnel were quantitatively analyzed.Based on the monitored data,theoretical calculation and experience of similar tunnels,considering relative deformation,strength stress ratio,ground stress,elastic ratio and comprehensive coefficient α as classification indexes,the classification criterion and measures to prevent large deformation of squeezing ground tunnels were worked out.
Abstract：
In natural element method,the trial and test functions were constructed with the natural neighbor interpolation method.The interpolation was based on the Voronoi tessellation of the scattered nodes in the problem domain.The integration of the weak form was performed in the Delaunay triangles which were the dual diagram of the Voronoi tessellation when the Galerkin method was used to form the discrete system equation.But there was obvious error in the numerical integration of the natural element method due to the characteristics of natural neighbor interpolation function.Every factor that produced the error possibly was analyzed,and a method using Monte Carlo integration was proposed to solve this problem.The weight coefficient was directly related to the precision,and its determination was also simple and effective.Integral point was cast in the Delaunay triangle,so the result of probability integral was close to mathematical expectation.The definite method of the least integral points,was given so as to enhance computational efficiency of the Monte Carlo integral as far as possible.Finally,the numerical example of the patch experiment and the cantilever beam confirmed the validity and feasibility of using Monte Carlo integration to solve these errors.
In natural element method,the trial and test functions were constructed with the natural neighbor interpolation method.The interpolation was based on the Voronoi tessellation of the scattered nodes in the problem domain.The integration of the weak form was performed in the Delaunay triangles which were the dual diagram of the Voronoi tessellation when the Galerkin method was used to form the discrete system equation.But there was obvious error in the numerical integration of the natural element method due to the characteristics of natural neighbor interpolation function.Every factor that produced the error possibly was analyzed,and a method using Monte Carlo integration was proposed to solve this problem.The weight coefficient was directly related to the precision,and its determination was also simple and effective.Integral point was cast in the Delaunay triangle,so the result of probability integral was close to mathematical expectation.The definite method of the least integral points,was given so as to enhance computational efficiency of the Monte Carlo integral as far as possible.Finally,the numerical example of the patch experiment and the cantilever beam confirmed the validity and feasibility of using Monte Carlo integration to solve these errors.
Abstract：
The influence of the construction machinery eccentric load on trench stability was studied by centrifuge model tests simulating the process of trench excavation.It was shown that the failure mechanism agreed well with that under the central load of construction machine.Therefore,the simplified expression for the upper-bound of excavation depth under the central load could be applied to that under the construction machinery eccentric load.The validity of the results from the simplified expression for the upper-bound solution was confirmed by comparing with the centrifuge test results.It was indicated that the influence of eccentricity on excavation depth increased with the increase of contact pressure.
The influence of the construction machinery eccentric load on trench stability was studied by centrifuge model tests simulating the process of trench excavation.It was shown that the failure mechanism agreed well with that under the central load of construction machine.Therefore,the simplified expression for the upper-bound of excavation depth under the central load could be applied to that under the construction machinery eccentric load.The validity of the results from the simplified expression for the upper-bound solution was confirmed by comparing with the centrifuge test results.It was indicated that the influence of eccentricity on excavation depth increased with the increase of contact pressure.
Abstract：
Because of the construction disturbance,the existing subway would be influenced when a new subway was built near it.When the influence reached a certain degree,the operating security of the existing subway would be threatened.For increasing the project security or decreasing the construction difficulty,lifting the existing subway by grouting was used in general to recover its elevation and to decrease differential settlement during or after the construction.The model of lifting the existing subway by grouting was created and the concept of grouting in the weak position was put forward.It was indicated that grouting in the week position would decrease the settlement and induce little stress concentration.The practical grouting program of the existing Beijing subway line 5 in the Chongwenmen station was analyzed.It was indicated that the settlement was decreased by grouting,but the degree of the stress concentration was some how large.Therefore,the lifting effect was significant and the safety of the existing subway in operation was increased.
Because of the construction disturbance,the existing subway would be influenced when a new subway was built near it.When the influence reached a certain degree,the operating security of the existing subway would be threatened.For increasing the project security or decreasing the construction difficulty,lifting the existing subway by grouting was used in general to recover its elevation and to decrease differential settlement during or after the construction.The model of lifting the existing subway by grouting was created and the concept of grouting in the weak position was put forward.It was indicated that grouting in the week position would decrease the settlement and induce little stress concentration.The practical grouting program of the existing Beijing subway line 5 in the Chongwenmen station was analyzed.It was indicated that the settlement was decreased by grouting,but the degree of the stress concentration was some how large.Therefore,the lifting effect was significant and the safety of the existing subway in operation was increased.
Abstract：
Based on the newly developed anisotropic elastic visco-plastic constitutive model for K0 consolidated clays,the expressions of preconsolidation pressure and undrained triaxial shear strength were presented,and their strain-rate dependencies were investigated.The strain rate parameter of undrained shear strength was a constant which just depends on the ratio of the consoliation coefficient to the secondary compression index,but the corresponding parameter of preconsolidation pressure was dependent on this ratio as well as the compression parameter Λ.For most inorganic clays,the preconsolidation pressure and undrained strength would increase by 8%21.2% and 7.2%12.2% respectively with a tenfold increase in the strain rate.Considering the differences of strain rate between the laboratory test and the field condition,it is suggested that the measured preconsolidation pressure and undrained strength should be modified before applied to the in-situ condition.As OCR increases,the increasing rate of the strength ratio with strain rate becomes faster.
Based on the newly developed anisotropic elastic visco-plastic constitutive model for K0 consolidated clays,the expressions of preconsolidation pressure and undrained triaxial shear strength were presented,and their strain-rate dependencies were investigated.The strain rate parameter of undrained shear strength was a constant which just depends on the ratio of the consoliation coefficient to the secondary compression index,but the corresponding parameter of preconsolidation pressure was dependent on this ratio as well as the compression parameter Λ.For most inorganic clays,the preconsolidation pressure and undrained strength would increase by 8%21.2% and 7.2%12.2% respectively with a tenfold increase in the strain rate.Considering the differences of strain rate between the laboratory test and the field condition,it is suggested that the measured preconsolidation pressure and undrained strength should be modified before applied to the in-situ condition.As OCR increases,the increasing rate of the strength ratio with strain rate becomes faster.
2008, 30(5): 726-731.
Abstract：
The strength and deformation behavior of municipal solid waste(MSW) with different composition was studied.A bilinear strain hardening model was proposed based on the results from the static triaxial tests under loading-unloading-reloading conditions.Furthermore,a complete set of model parameters including unloading modulus and Poisson’s ratio were determined.It was shown that stress-strain relationship of MSW was significantly affected by MSW composition and its compacted density.MSW was divided into two categories based on the ratio of organic fraction to inorganic fraction,and different models were used to describe corresponding types of MSW.It was found that there were marked strain hardening characteristics in the stress-strain relationship of MSW when the majority of its composition was organic component,and a bilinear model was proved to be more reasonable to describe this type of MSW.Whereas,the stress-strain behavior of MSW was similar with that of soil when the majority of its composition was inorganic,and the hyperbola model could be used to describe the stress-strain relationship of this type of MSW.
The strength and deformation behavior of municipal solid waste(MSW) with different composition was studied.A bilinear strain hardening model was proposed based on the results from the static triaxial tests under loading-unloading-reloading conditions.Furthermore,a complete set of model parameters including unloading modulus and Poisson’s ratio were determined.It was shown that stress-strain relationship of MSW was significantly affected by MSW composition and its compacted density.MSW was divided into two categories based on the ratio of organic fraction to inorganic fraction,and different models were used to describe corresponding types of MSW.It was found that there were marked strain hardening characteristics in the stress-strain relationship of MSW when the majority of its composition was organic component,and a bilinear model was proved to be more reasonable to describe this type of MSW.Whereas,the stress-strain behavior of MSW was similar with that of soil when the majority of its composition was inorganic,and the hyperbola model could be used to describe the stress-strain relationship of this type of MSW.
Abstract：
Due to the limitation of the numerical models of rock bolts by finite element method(FEM) in geotechnical engineering,the bolt model for the FEM of strength reduction method and the optimization of anchor parameters was suggested.The model could consider the friction along the bolts.Then the corresponding program for the bolt model was developed.The model was used in the calculation of anchor projects in rock slopes.It was indicated that the model was convenient and feasible,and the applicability of the numerical simulation for the reinforced rock mass was enhanced.
Due to the limitation of the numerical models of rock bolts by finite element method(FEM) in geotechnical engineering,the bolt model for the FEM of strength reduction method and the optimization of anchor parameters was suggested.The model could consider the friction along the bolts.Then the corresponding program for the bolt model was developed.The model was used in the calculation of anchor projects in rock slopes.It was indicated that the model was convenient and feasible,and the applicability of the numerical simulation for the reinforced rock mass was enhanced.
Abstract：
Field tests on the sheet-pile walls in a highway were performed and the stress of steel bar,lateral deformation of test piles and pulling force of pre-stressed anchor cables were observed.The process of anchor-stretching were reckoned as two conditions signed as BI,BII,while the process of filling was divided into three conditions signed as AI,AII,AIII.It was shown that: ① At the end of condition AI,the maximum moment appeared and the most part of displacement at the top of the test piles appeared during construction.So the time of transition from the filling to the anchor-stretching had great influence on the inner force of the piles.The most dangerous state maybe appeared under the condition AI.② Under the condition BI,the moment value was reduced slightly and the deformation of the piles was restored partly.After anchored,the reduction of the bending moment and the displacement of the top of the piles were unremarkable,so the cables should be loaded as early as possible to make the inner force of the piles more reasonable.③ The growing rate of the moment in the test piles above the ground descended sharply under the condition AII by contrast with that under the condition AI and the moment of the test piles increased more remarkably near the anchor cables than the moment of other part,furthermore,the most remarkable variation of moment of the piles was found at section of the lower anchor under the condition BII.④ The variation of the moment of the test piles mainly occurred near the upper anchor under the condition AIII.It was indicated that there was a great effect of the construction steps on the inner force and lateral deformation of piles,so the construction conditions should be optimized and the checking calculation should be done when the piles were designed.In order to ensure the safety of the walls during construction,the construction procedure should be clearly regulated.
Field tests on the sheet-pile walls in a highway were performed and the stress of steel bar,lateral deformation of test piles and pulling force of pre-stressed anchor cables were observed.The process of anchor-stretching were reckoned as two conditions signed as BI,BII,while the process of filling was divided into three conditions signed as AI,AII,AIII.It was shown that: ① At the end of condition AI,the maximum moment appeared and the most part of displacement at the top of the test piles appeared during construction.So the time of transition from the filling to the anchor-stretching had great influence on the inner force of the piles.The most dangerous state maybe appeared under the condition AI.② Under the condition BI,the moment value was reduced slightly and the deformation of the piles was restored partly.After anchored,the reduction of the bending moment and the displacement of the top of the piles were unremarkable,so the cables should be loaded as early as possible to make the inner force of the piles more reasonable.③ The growing rate of the moment in the test piles above the ground descended sharply under the condition AII by contrast with that under the condition AI and the moment of the test piles increased more remarkably near the anchor cables than the moment of other part,furthermore,the most remarkable variation of moment of the piles was found at section of the lower anchor under the condition BII.④ The variation of the moment of the test piles mainly occurred near the upper anchor under the condition AIII.It was indicated that there was a great effect of the construction steps on the inner force and lateral deformation of piles,so the construction conditions should be optimized and the checking calculation should be done when the piles were designed.In order to ensure the safety of the walls during construction,the construction procedure should be clearly regulated.
2008, 30(5): 745-749.
Abstract：
Aiming at the acoustic emission behaviors of aplite granite in Portugal,several uniaxil compressive tests with cyclic loadings were carried out on the same rock sample for monitoring acoustic emission activities and recording deformation of rock in order to acquire the relationship between them.It was found that the more the stress exerted on the rock sample,the weaker Kaiser effect became.But in balance,Kaiser effect existed profoundly in aplite granite even when the specimen was under high stress.To determine Kaiser point,using time-cumulative energy curve was easier and more reasonable than using time-cumulative AE events curve,as the inflection point in time-cumulative energy curve was so easy to be obtained.Furthermore,a good understanding on compression-deformation behavior of rock was a beneficial supplement for the explanation of acoustic emission test results.
Aiming at the acoustic emission behaviors of aplite granite in Portugal,several uniaxil compressive tests with cyclic loadings were carried out on the same rock sample for monitoring acoustic emission activities and recording deformation of rock in order to acquire the relationship between them.It was found that the more the stress exerted on the rock sample,the weaker Kaiser effect became.But in balance,Kaiser effect existed profoundly in aplite granite even when the specimen was under high stress.To determine Kaiser point,using time-cumulative energy curve was easier and more reasonable than using time-cumulative AE events curve,as the inflection point in time-cumulative energy curve was so easy to be obtained.Furthermore,a good understanding on compression-deformation behavior of rock was a beneficial supplement for the explanation of acoustic emission test results.
Abstract：
Compared the results of laboratory triaxial tests with those of biaxial tests in the particle flow code,the microscopic parameters were determined,and sand characteristics in particle flow code were simulated.Simulation of soil arching by particle flow code was proven feasible through comparison of the results of trapdoor simulated by particle flow code with those of trapdoor tests.Based on the above study,the model of particle flow code was established for simulation on relaxation effect of vertical earth pressure in shield tunneling,and then was used to analyze the earth pressure on the lining,earth displacement and contact force between soil particles considering the factors of ground loss,buried depth and diameter of tunnels and soil properties.It was indicated that the soil arching mainly took place within the range of soil of 12 times the tunnel diameter above the tunnel,and that the earth pressure acting on the tunnel lining decreased greatly because of the soil arching.
Compared the results of laboratory triaxial tests with those of biaxial tests in the particle flow code,the microscopic parameters were determined,and sand characteristics in particle flow code were simulated.Simulation of soil arching by particle flow code was proven feasible through comparison of the results of trapdoor simulated by particle flow code with those of trapdoor tests.Based on the above study,the model of particle flow code was established for simulation on relaxation effect of vertical earth pressure in shield tunneling,and then was used to analyze the earth pressure on the lining,earth displacement and contact force between soil particles considering the factors of ground loss,buried depth and diameter of tunnels and soil properties.It was indicated that the soil arching mainly took place within the range of soil of 12 times the tunnel diameter above the tunnel,and that the earth pressure acting on the tunnel lining decreased greatly because of the soil arching.
2008, 30(5): 755-759.
Abstract：
Monitoring of the stress distribution along anchor bolts is a critical issue for ground anchorage engineering.Considering the characteristics of distributed fiber optic sensing technology—Brillouin optical time-domain reflectometer(BOTDR),the layout and installation of the sensing fiber on anchor bolts were designed.Combining the pull-out tests on anchor bolts,the feasibility of this method was discussed.The test results demonstrated that BOTDR-based distributed fiber optic sensing technology had some unique advantages,such as easy installation and large measurement range.It could veritably detect the axial strain and stress distribution of the anchor bolts under different levels of load.Thus the conclusion could be drawn that BOTDR-based distributed monitoring technology had wide application prospect in geotechnical engineering.
Monitoring of the stress distribution along anchor bolts is a critical issue for ground anchorage engineering.Considering the characteristics of distributed fiber optic sensing technology—Brillouin optical time-domain reflectometer(BOTDR),the layout and installation of the sensing fiber on anchor bolts were designed.Combining the pull-out tests on anchor bolts,the feasibility of this method was discussed.The test results demonstrated that BOTDR-based distributed fiber optic sensing technology had some unique advantages,such as easy installation and large measurement range.It could veritably detect the axial strain and stress distribution of the anchor bolts under different levels of load.Thus the conclusion could be drawn that BOTDR-based distributed monitoring technology had wide application prospect in geotechnical engineering.
Abstract：
Silty slurry would be anisotropic quickly because of the deposit of silt.In order to take this anisotropy into account,equations were established to analyze the shape and mechanical behavior of geotextile bags assuming that the density of the slurry increased linearly,and the numerical method to this solution was given.It was shown that the geometry of the geotextile bags with anisotropic slurry was flatter,and the tensile was larger than that in the case of homogeneous slurry.Therefore,it was necessary to take the anisotropy of silty slurry into account.
Silty slurry would be anisotropic quickly because of the deposit of silt.In order to take this anisotropy into account,equations were established to analyze the shape and mechanical behavior of geotextile bags assuming that the density of the slurry increased linearly,and the numerical method to this solution was given.It was shown that the geometry of the geotextile bags with anisotropic slurry was flatter,and the tensile was larger than that in the case of homogeneous slurry.Therefore,it was necessary to take the anisotropy of silty slurry into account.
Abstract：
A series of undrained cyclic triaxial tests were performed on soft clays including undisturbed and remolded samples.The transient cumulative strains under the cyclic loading with or without the initial static deviatoric stress were analyzed,and a constitutive strain model considering the cyclic stress,cycle number,OCR and initial static deviatoric stress was proposed.It was shown that the deformation of soft clay was seriously influenced by the confining pressure and the failure of soil structure.When the confining pressure was larger than the yielding pressure of the undisturbed clay,the deformation characteristics would be close to those of the remolded clay.For these two kinds of samples,there existed a turning point on strain curves under the cyclic loading,indicating failure of soil structure,and the deformation of soil before and after this structure failure should be described separately.
A series of undrained cyclic triaxial tests were performed on soft clays including undisturbed and remolded samples.The transient cumulative strains under the cyclic loading with or without the initial static deviatoric stress were analyzed,and a constitutive strain model considering the cyclic stress,cycle number,OCR and initial static deviatoric stress was proposed.It was shown that the deformation of soft clay was seriously influenced by the confining pressure and the failure of soil structure.When the confining pressure was larger than the yielding pressure of the undisturbed clay,the deformation characteristics would be close to those of the remolded clay.For these two kinds of samples,there existed a turning point on strain curves under the cyclic loading,indicating failure of soil structure,and the deformation of soil before and after this structure failure should be described separately.
Abstract：
The anomalously low friction phenomenon is one of the typical dynamic phenomena in the deep block rock mass,reflecting the inconsistent and inconsecutive dynamic characteristics of deep block rock mass.Based on the anomalously low friction test carried by Russian academician Kurlenya M V,a one-dimensional dynamic model was established,and the analytical solution of transverse displacement of working block was obtained.It was demonstrated that the analytical results based on the one-dimensional dynamic model agreed well with the experimental data.The geo-mechanical condition for the occurrence of the anomalously low friction phenomenon lied in the canonical coordination of delay intervals between the vertical and horizontal pulse impact on the block system and the working block respectively,and its formation mechanism rested on the redistribution of vertical force and variation of dynamic friction factors between blocks under the powerful impact,and the discrete periods of anomalously low friction phenomenon were closely related with the spectrums of low-frequency low-speed reversal pendulum-type wave.
The anomalously low friction phenomenon is one of the typical dynamic phenomena in the deep block rock mass,reflecting the inconsistent and inconsecutive dynamic characteristics of deep block rock mass.Based on the anomalously low friction test carried by Russian academician Kurlenya M V,a one-dimensional dynamic model was established,and the analytical solution of transverse displacement of working block was obtained.It was demonstrated that the analytical results based on the one-dimensional dynamic model agreed well with the experimental data.The geo-mechanical condition for the occurrence of the anomalously low friction phenomenon lied in the canonical coordination of delay intervals between the vertical and horizontal pulse impact on the block system and the working block respectively,and its formation mechanism rested on the redistribution of vertical force and variation of dynamic friction factors between blocks under the powerful impact,and the discrete periods of anomalously low friction phenomenon were closely related with the spectrums of low-frequency low-speed reversal pendulum-type wave.
Abstract：
Based on the principle of Mahalanobis distance discriminant analysis,the distance analytic model was applied to the prediction of sand liquefaction with eight factors listed as follows: mean diameter,coefficient of non-uniformity,blow number of standard penetration test,underground water depth,sand depth,ratio of shearing stress to effective overburden stress,seismic intensity,epicenteral distance.Through computing practical examples and assessing the model,the model was manifested to be scientific and effective with much more accurate results than the normalization methods and simplified Seed method.It was shown that the present method was efficient in solving the prediction of sand liquefaction and could be applied to practical engineering.
Based on the principle of Mahalanobis distance discriminant analysis,the distance analytic model was applied to the prediction of sand liquefaction with eight factors listed as follows: mean diameter,coefficient of non-uniformity,blow number of standard penetration test,underground water depth,sand depth,ratio of shearing stress to effective overburden stress,seismic intensity,epicenteral distance.Through computing practical examples and assessing the model,the model was manifested to be scientific and effective with much more accurate results than the normalization methods and simplified Seed method.It was shown that the present method was efficient in solving the prediction of sand liquefaction and could be applied to practical engineering.
