The deformation energy(Wd)of soil-like tectonic coal is crucial for investigating the mechanism of coal and gas outbursts.Tectonic coal has a significant nonlinear constitutive relationship,which makes traditional ela...The deformation energy(Wd)of soil-like tectonic coal is crucial for investigating the mechanism of coal and gas outbursts.Tectonic coal has a significant nonlinear constitutive relationship,which makes traditional elastic-based models for computing Wdunsuitable.Inspired by critical state soil mechanics,this study theoretically established a new calculation model of Wdsuitable for the coal with nonlinear deformation characteristics.In the new model,the relationship between energy and stress no longer follows the square law(observed in traditional linear elastic models)but exhibits a power function,with the theoretical value of the power exponent ranging between 1 and 2.Hydrostatic cyclic loading and unloading experiments were conducted on four groups of tectonic coal samples and one group of intact coal samples.The results indicated that the relationship between Wdand stress for both intact and tectonic coal follows a power law.The exponents for intact and tectonic coal are close to 2 and 1,respectively.The stress-strain curve of intact coal exhibits small deformation and linear characteristics,whereas the stress-strain curves of tectonic coal show large deformation and nonlinear characteristics.The study specifically investigates the role of coal viscosity in the cyclic loading/unloading process.The downward bending in the unloading curves can be attributed to the time-dependent characteristics of coal,particularly its viscoelastic behavior.Based on experimental statistics,the calculation model of Wdwas further simplified.The simplified model involves only one unknown parameter,which is the power exponent between Wdand stress.The measured Wdof the coal samples increases with the number of load cycles.This phenomenon is attributed to coal's viscoelastic deformation.Within the same stress,the Wdof tectonic coal is an order of magnitude greater than that of intact coal.The calculation model of Wdproposed in this paper provides a new tool for studying the energy principle of coal and gas outbursts.展开更多
The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by ...The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by the common self-similar-based similarity techniques.This paper proposes a novel,exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils.Considering stress-dependent elastic moduli of soils,new analytical stress and displacement solutions for the nonself-similar problem are developed taking the small strain assumption in the elastic zone.In the plastic zone,the cavity expansion response is formulated into a set of first-order partial differential equations(PDEs)with the combination use of Eulerian and Lagrangian descriptions,and a novel solution algorithm is developed to efficiently solve this complex boundary value problem.The solution is presented in a general form and thus can be useful for a wide range of soils.With the new solution,the non-self-similar nature induced by the finite outer boundary is clearly demonstrated and highlighted,which is found to be greatly different to the behaviour of cavity expansion in infinite soil mass.The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small-sized calibration chambers.展开更多
The disposal of filtered tailings in high dry stacks can induce particle breakage,changing the material's behaviour during the structure's lifetime.The grading changes influence material properties at the crit...The disposal of filtered tailings in high dry stacks can induce particle breakage,changing the material's behaviour during the structure's lifetime.The grading changes influence material properties at the critical state,and this is not mature for intermediate artificial soils(tailings)in a broad range of confining pressures.In this paper,it aims to describe the behaviour of iron ore tailings in a spectrum of confining pressures broader than the reported in previous studies.A series of consolidated drained(CD)triaxial tests was carried out with confining pressures ranging from 0.075 MPa to 120 MPa.These results show that the amount of breakage plays an essential role in the response of iron ore tailings.The existence of curved critical state line(CSL)in both specific volume(ν)-logarithm of mean effective stress(p′)and deviatoric stress(q)-mean effective stress(p′)planes,and different responses in the deviatoric stress-axial strain-volumetric strain curves were verified.An inverse S-shaped equation was proposed to represent the silty-sandy tailings'behaviour up to high pressures onν-lnp′plane.The proposed equation provides a basis for enhancing constitutive models and considers the evolution of the grading up to severe loading conditions.The adjustment considered three regions with different responses associated with particle breakage at different pressure levels.展开更多
The compression behavior responsible for unity sensitivity is very valuable in quantitative assessment of the effects of soil structure on the compression behavior of soft marine sediments. However, the quantitative a...The compression behavior responsible for unity sensitivity is very valuable in quantitative assessment of the effects of soil structure on the compression behavior of soft marine sediments. However, the quantitative assessment of such effects is not possible because of unavailability of the formula for the compression curve of marine sediments responsible for unit sensitivity. In this study, the relationship between the remolded state and the conventional critical state line is presented in the deviator stress versus mean effective stress plot. The analysis indicates that the remolded state is on the conventional critical state line obtained at a relatively small strain. Thus, a unique critical state sedimentation line for marine sediments of unit sensitivity is proposed. The comparison between the critical state sedimentation line proposed in this study and the existing normalized consolidation curves obtained from conventional oedometer tests on remolded soils or reconstituted soils explains well the展开更多
In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intac...In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now,leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD,and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comprehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions.展开更多
A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework o...A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework of critical state soil mechanics and modified Cam-clay model. The existing model hasbeen generalized to simulate the experimentally observed behavior of unsaturated clays by introducingBishop＇s stress and suction as independent stress parameters and modifying the hardening rule and yieldcriterion to take into account the role of suction. Also, according to previous studies, an increase intemperature causes a reduction in specific volume. A reduction in suction （wetting） for a given confiningstress may induce an irreversible volumetric compression （collapse）. Thus an increase in suction （drying）raises a specific volume i.e. the movement of normal consolidation line （NCL） to higher values of voidratio. However, some experimental data confirm the assumption that this reduction is dependent on thestress level of soil element. A generalized approach considering the effect of stress level on themagnitude of clays thermal dependency in compression plane is proposed in this study. The number ofmodeling parameters is kept to a minimum, and they all have clear physical interpretations, to facilitatethe usefulness of model for practical applications. A step-by-step procedure used for parameter calibrationis also described. The model is finally evaluated using a comprehensive set of experimental datafor the thermo-mechanical behavior of unsaturated soils.2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently develo...Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently developed SIMSAND critical state sand model combined with the smoothed particle hydrodynamics(SPH)method is adopted in this work to study slope failure under large deformations.To illustrate the efficiency and accuracy of the SIMSAND-SPH approach,a series of slope collapse studies using the discrete element method(DEM)considering various particle shapes(i.e.spherical,tetrahedral and elongated)is adopted as benchmarks.The parameters of the SIMSAND model are calibrated using DEM triaxial tests.In comparison to the DEM simulations,the runout distance and final slope height are well characterized with the SIMSAND-SPH approach with less computational cost.All comparisons show that the SIMSAND-SPH approach is highly efficient and accurate,which can be an alternative numerical tool to simulate real scale granular flow.展开更多
The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for enginee...The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for engineering design and practice.In this paper,we propose a novel numerical approach to study soil collapse involving large deformation.The approach combines a recently developed critical state-based sand model SIMSAND for describing complex sand mechanical behaviors,and the smoothed particle hydrodynamics(SPH)method for dealing with large deformation.To show the high efficiency and accuracy of the proposed approach,a series of column collapses using discrete element method(DEM)and considering the influence of particle shapes(i.e.spherical shape(SS),tetrahedral shape(TS),and elongated shape(ES))were adopted as benchmarks and simulated by the proposed method.The parameters of SIMSAND were calibrated from the results of DEM triaxial tests on the same samples.Compared with the results of DEM simulations and reference solutions derived by published collapse experiments,the runout distance and final height of specimens with different particle shapes simulated by SPH-SIMSAND were well characterized and incurred a lower computational cost.Comparisons showed that the novel SPH-SIMSAND approach is highly efficient and accurate for simulating collapse,and can be a useful numerical analytical tool for real scale engineering problems.展开更多
Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years.A series of consolidated drained triaxial compression tests has been conducted here to examine the effect...Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years.A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand.Sand with 0%,0.2%,0.4%,and 1%fiber contents,prepared to yield random distribution,was sheared under several confining pressures and controlled via their initial relative densities.The test results showed that the maximum and residual deviatoric stresses increased,whereas the volumetric expansion decreased with an increase in fiber content.Although the stress ratio h(=q/p′)and specific volume changed depending on the fiber content and confining pressure with shear progression,they each reached the same values for a definite fiber content at the end of shearing,independent of initial relative density.In other words,the unique critical state line can be found for a definite fiber content.Moreover,the greater the fiber content,the larger the slope of the critical state line at the end of shearing.Additionally,as the length of fibers shortened with the same percentage of fiber inclusions in sand,the deviatoric stress and the stress ratio decreased,approaching the shear-strain-volumetric response of unreinforced sand.展开更多
There have been significant advances in the application of critical state,CS,in liquefaction potential assessment.This was done by comparing state parameter,j with estimated characteristic cyclic stress ratio,CSR due ...There have been significant advances in the application of critical state,CS,in liquefaction potential assessment.This was done by comparing state parameter,j with estimated characteristic cyclic stress ratio,CSR due to an earthquake.A cyclic resistance ratio,CRR curve,which can be determined from cyclic liquefaction tests,separates historical liquefied and non-liquefied data points(j,CSR).On the other hand,the concepts of equivalent granular state parameter,j*,which was developed for sands with fines,can be used in lieu j to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines,irrespective of fines content(fc).The present work combines these two propositions,and by merely substituting j*for j into the aforementioned CS approach to capture the influence of fc.A series of static and cyclic triaxial tests were conducted,separately and independently of the concept of j*,for sand with up to fc of 30%.The clean sand was collected from Sabarmati river belt at Ahmedabad city in India which was severely affected during the Bhuj earthquake,2001.The experimental data gave a single relation for CRR and j*which was then used to assess liquefaction potential for a SPT based case study,where fc varies along the depth.The prediction matched with the field observation.展开更多
Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of partic...Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.展开更多
This paper investigates the strength and critical state(CS)behaviours of granular materials via DEM simulations of true triaxial drained tests under three different loading modes including constant b(in-termediate str...This paper investigates the strength and critical state(CS)behaviours of granular materials via DEM simulations of true triaxial drained tests under three different loading modes including constant b(in-termediate stress ratio)tests with constantσ'1(major principal stress),constant p(mean pressure)and constantσ'3(minor principal stress)respectively.To this end,a series of samples are generated with the same particle size distribution,and with the confining stresses ranging from 100 kPa to 900 kPa.The CS is achieved for all samples.Both the macroscopic behaviours and the microscopic behaviours are examined and compared considering different loading modes,confining stresses and intermediate stress ratios(b).The critical state lines(CSLs)are found to be unique and independent of the loading modes,but dependent on the b values.The CSLs with b=0 and b=1 form the two boundaries of CSLs respectively beyond which CSLs under all other b tests cannot go beyond.Six different strength criteria are examined and compared in terms of both peak and CS failures.The Mohr-Coulomb strength criterion is found to be only suitable for axisymmetric loading conditions.The Lade-Duncan criterion is only suitable for describing peak strengths,which is dependent on the loading modes and confining stresses.The Satake criterion and Matsuoka-Nakai criterion are the more appropriate strength criteria for describing CS failures,indicating that the CS values of both the Satake parameter and the Matsuoka-Nakai parameter describe an inherent property that characterizes the CS failure for a given type of soil.The CS mechanical coordination number is fitted by a curved line for a given b value,which is unique regardless of the loading modes.The peak and CS values of both major and minor principal fabric tensors decrease with increasing b values,while they increase with increasing b values for the intermediate principal fabric tensor.展开更多
Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization ...Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization and good magnetic softness(high permeability and low core loss).In this work,utilizing the order modulation strategy,a critical state in a FeSiBCCr amorphous soft magnetic composite(ASMC),consisting of massive crystal-like orders(CLOs,∼1 nm in size)with the feature ofα-Fe,is designed.This critical-state structure endows the amorphous powder with the enhanced ferromagnetic exchange interactions and the optimized magnetic domains with uniform orientation and fewer micro-vortex dots.Superior comprehensive soft magnetic properties at high frequency emerge in the ASMC,such as a high saturation magnetization(Ms)of 170 emu g^(-1)and effective permeability(µ_(e))of 65 combined with a core loss(Pcv)as low as 70 mW cm^(-3)(0.01 T,1 MHz).This study provides a new strategy for the development of high-frequency ASMCs,possessing suitable comprehensive soft magnetic performance to match the requirements of the modern magnetic devices used in the third-generation semiconductors and new energy fields.展开更多
Particle breakage has a significant influence on the stress-strain and strength behavior of rockfill material.A breakage critical state theory(BCST)was proposed to describe the evolution of particle breakage.The break...Particle breakage has a significant influence on the stress-strain and strength behavior of rockfill material.A breakage critical state theory(BCST)was proposed to describe the evolution of particle breakage.The breakage critical state line in the breakage critical state theory was correlated with the breakage factor,which was fundamentally different from that of the original critical state theory.A simple elastoplastic constitutive model was developed for rockfill in the frame of BCST.An associated flow rule was adopted in this model.Isotropic,contractive and distortional hardening rules were suggested in view of the particle breakage.It was observed that the proposed model could well represent the complex deformation behaviors of rockfill material,such as the strain hardening,post-peak strain softening,volumetric contraction,volumetric expansion,and particle breakage under different initial confining pressures.展开更多
The interface between soil and structure can be referred to as a soil-structure system, and its behavior plays an important role in many geotechnical engineering practices, In this study, results are presented from a ...The interface between soil and structure can be referred to as a soil-structure system, and its behavior plays an important role in many geotechnical engineering practices, In this study, results are presented from a series of monotonic direct shear tests performed on a sand-structure interface under constant normal stiffness using the discrete element method （DEM）. Strain localization and dilatancy behavior of the interface is carefully examined at both macroscopic and microscopic scales. The effects of soil initial relative density and normal stress on the interface shear behavior are also investigated, The results show that a shear band progressively develops along the structural surface as shear displacement increases. At large shear displacement a unique relationship between stress ratio and void ratio is reached in the shear band for a certain normal stress, indicating that a critical state exists in the shear band. It is also found that the thickness and void ratio of the shear band at the critical state decreases with increasing normal stress. Comparison of the DEM simulation results with experimental results provides insight into the shear behavior of a sand-structure interface and offers a means for quantitative modeling of such interfaces based on the critical state soil mechanics.展开更多
The critical state soil mechanics(CSSM)framework has been widely used across a range of problems in geomechanics involving complex loading conditions.However,the uniqueness of the critical state has been disputed for ...The critical state soil mechanics(CSSM)framework has been widely used across a range of problems in geomechanics involving complex loading conditions.However,the uniqueness of the critical state has been disputed for many years and it remains a controversial issue.Motivated by previous investigations,a series of discrete element method(DEM)simulations were performed under both axial compression(AC)and axial extension(AE)stress paths.All samples were isotropically compressed at varying mean normal effective stresses(confining pressures)and sheared to a large axial strain of approximately 60%.It is found that there exist unique values of critical void ratios and stress ratios under critical state,which are independent of the samples’initial packings but dependent on stress paths.And the critical strength(stress ratio)for the AC stress path tests is higher than that for the AE stress path.The critical state lines(CSLs)are found to path-dependent but unique for each stress path.A unique linear relationship between the critical coordination numbers and critical void ratios is identified under the AC and AE stress paths respectively,but such a relationship depends on the stress paths.It is also found that there exist unique values of microscopic parameters in terms of deviator fabric under critical state,which are independent of the samples’initial packings but dependent on stress paths.All these simulation results lead to the conclusion of non-uniqueness of CSLs from both macroscopic and microscopic viewpoints.展开更多
The present study investigates the critical state behaviour of granular assemblies composed of clumped particles under four different drained axisymmetric triaxial stress paths,using the discrete element method(DEM).A...The present study investigates the critical state behaviour of granular assemblies composed of clumped particles under four different drained axisymmetric triaxial stress paths,using the discrete element method(DEM).A series of numerical samples were prepared at initial states with different density indexes(1D)and different initial confining pressures(ρ′0).These samples were sheared to large strains,at which constant stresses and volumes were maintained to reach the critical state.The evolution of stress ratio under the same loading mode(for the same intermediate principal stress ratio,b)is shown to yield an almost identical behaviour independent of stress paths,whereas the stress-strain response depends on the stress paths.Four different axisymmetric stress paths all share the same unique friction angle at critical state,indicating the Mohr-Coulomb failure criterion is the appropriate critical state strength criterion,which is at least true for the axisymmetric stress conditions.A unique coordination number(CN)is achieved at the critical state for a given po,which is independent of the stress path.The critical state CN is found to increase with the increase in po,which could be attributed to the decrease in the critical state void ratio(ec)as mean effective stress(ρ′0)increases.Interestingly,a unique linear functional relationship is found between the critical state values of cN and ec,and a unique polynomial functional relationship is found between the critical state values of CN andρ′.These functional relationships indicate no dependency on the stress paths or loading modes,thus characterizing unique features at critical states at both macroscopic and microscopic levels for a given type of granular material.展开更多
Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have en...Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.展开更多
The effectiveness of using vegetation to stabilise shallow soil slopes heavily depends on the survival of vegetation,yet the amplification of extreme events induced by climate change threatens the health of plants cov...The effectiveness of using vegetation to stabilise shallow soil slopes heavily depends on the survival of vegetation,yet the amplification of extreme events induced by climate change threatens the health of plants covering slopes.Hydrochar is an environmentally friendly soil amender that can achieve the potential benefits of promoting plant growth for slope stabilisation and facilitation of waste upcycling.The mechanism underlying the hydrochar effects on the mechanical behaviour of unsaturated soils remains unclear.This study investigated the influence of grass-derived hydrochar on the water retention,compressibility,and shear strength of a compacted siltyeclay sand.Soil microstructural changes due to hydrochar amendment were measured to explain the soilehydrochar hydromechanical interaction.The increase in suction resulted in a less significant increase in yield stress and a negligible reduction in compressibility of the hydrochar-amended soil compared with the unamended case.This phenomenon was observed because hydrochar addition reduced the large pores with diameters greater than the macropore peak of 60 mm due to pore filling by hydrochar particles,resulting in a less substantial volume contraction during drying.Hydrochar introduced more significant effects on the soil’s shear strength in an unsaturated state compared to a saturated case.Despite the similarity of the unsaturated amended soil with the critical-state friction angle to the saturated case,the former exhibited a greater shear strength because the hydrochar addition improved water retention capability.As a result,the degree of saturation and,hence,Bishop’s effective stress were higher than those for the unamended case for a given suction.展开更多
This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis tra...This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique(ATT).Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio,matric suction,and confining pressure on the properties of CREFMs.Key findings reveal a primary suction range of 0 e100 kPa characterized by hysteresis,which intensifies with decreasing density.Notably,the air entry value and residual suction are influenced by void ratio,with higher void ratios leading to decreased air entry values and residual suctions,underscoring the critical role of void ratio in hydraulic behavior.Additionally,the critical state line(CSL)in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction,significantly affecting dilatancy and critical states.Furthermore,the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction.A novel modified dilatancy equation was proposed,which enhances the predictability of CREFMs'responses under variable loading,particularly at high stress ratios defined by the deviatoric stress over the mean effective stress.This research advances the understanding of CREFMs'performance,especially under fluctuating environmental conditions that alter suction levels.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(No.2024QN11072)National Natural Science Foundation of China(Nos.52404264 and 52174217)State Key Program of the National Natural Science Foundation of China(No.52034008)。
文摘The deformation energy(Wd)of soil-like tectonic coal is crucial for investigating the mechanism of coal and gas outbursts.Tectonic coal has a significant nonlinear constitutive relationship,which makes traditional elastic-based models for computing Wdunsuitable.Inspired by critical state soil mechanics,this study theoretically established a new calculation model of Wdsuitable for the coal with nonlinear deformation characteristics.In the new model,the relationship between energy and stress no longer follows the square law(observed in traditional linear elastic models)but exhibits a power function,with the theoretical value of the power exponent ranging between 1 and 2.Hydrostatic cyclic loading and unloading experiments were conducted on four groups of tectonic coal samples and one group of intact coal samples.The results indicated that the relationship between Wdand stress for both intact and tectonic coal follows a power law.The exponents for intact and tectonic coal are close to 2 and 1,respectively.The stress-strain curve of intact coal exhibits small deformation and linear characteristics,whereas the stress-strain curves of tectonic coal show large deformation and nonlinear characteristics.The study specifically investigates the role of coal viscosity in the cyclic loading/unloading process.The downward bending in the unloading curves can be attributed to the time-dependent characteristics of coal,particularly its viscoelastic behavior.Based on experimental statistics,the calculation model of Wdwas further simplified.The simplified model involves only one unknown parameter,which is the power exponent between Wdand stress.The measured Wdof the coal samples increases with the number of load cycles.This phenomenon is attributed to coal's viscoelastic deformation.Within the same stress,the Wdof tectonic coal is an order of magnitude greater than that of intact coal.The calculation model of Wdproposed in this paper provides a new tool for studying the energy principle of coal and gas outbursts.
基金funding support from the National Key Research and Development Program of China(Grant No.2023YFB2604004)the National Natural Science Foundation of China(Grant No.52108374)the“Taishan”Scholar Program of Shandong Province,China(Grant No.tsqn201909016)。
文摘The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by the common self-similar-based similarity techniques.This paper proposes a novel,exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils.Considering stress-dependent elastic moduli of soils,new analytical stress and displacement solutions for the nonself-similar problem are developed taking the small strain assumption in the elastic zone.In the plastic zone,the cavity expansion response is formulated into a set of first-order partial differential equations(PDEs)with the combination use of Eulerian and Lagrangian descriptions,and a novel solution algorithm is developed to efficiently solve this complex boundary value problem.The solution is presented in a general form and thus can be useful for a wide range of soils.With the new solution,the non-self-similar nature induced by the finite outer boundary is clearly demonstrated and highlighted,which is found to be greatly different to the behaviour of cavity expansion in infinite soil mass.The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small-sized calibration chambers.
文摘The disposal of filtered tailings in high dry stacks can induce particle breakage,changing the material's behaviour during the structure's lifetime.The grading changes influence material properties at the critical state,and this is not mature for intermediate artificial soils(tailings)in a broad range of confining pressures.In this paper,it aims to describe the behaviour of iron ore tailings in a spectrum of confining pressures broader than the reported in previous studies.A series of consolidated drained(CD)triaxial tests was carried out with confining pressures ranging from 0.075 MPa to 120 MPa.These results show that the amount of breakage plays an essential role in the response of iron ore tailings.The existence of curved critical state line(CSL)in both specific volume(ν)-logarithm of mean effective stress(p′)and deviatoric stress(q)-mean effective stress(p′)planes,and different responses in the deviatoric stress-axial strain-volumetric strain curves were verified.An inverse S-shaped equation was proposed to represent the silty-sandy tailings'behaviour up to high pressures onν-lnp′plane.The proposed equation provides a basis for enhancing constitutive models and considers the evolution of the grading up to severe loading conditions.The adjustment considered three regions with different responses associated with particle breakage at different pressure levels.
基金This research project was financially supported by the Ministry of Science and Technology, Japan(Domestic Research Fellowship, 1999-2001)
文摘The compression behavior responsible for unity sensitivity is very valuable in quantitative assessment of the effects of soil structure on the compression behavior of soft marine sediments. However, the quantitative assessment of such effects is not possible because of unavailability of the formula for the compression curve of marine sediments responsible for unit sensitivity. In this study, the relationship between the remolded state and the conventional critical state line is presented in the deviator stress versus mean effective stress plot. The analysis indicates that the remolded state is on the conventional critical state line obtained at a relatively small strain. Thus, a unique critical state sedimentation line for marine sediments of unit sensitivity is proposed. The comparison between the critical state sedimentation line proposed in this study and the existing normalized consolidation curves obtained from conventional oedometer tests on remolded soils or reconstituted soils explains well the
基金the International Collaboration Project on Coupled Fracture Mechanics Modelling(project team consisting of CSIRO,SDUST,Posiva,KIGAM,KICT,CAS-IRSM,DUT/Mechsoft,SNU,LBNL,ETH,Aalto Uni.,GFZ and TYUT)Taishan Scholar Talent Team Support Plan for Advantaged&Unique Discipline Areas,Shandong Province
文摘In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now,leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD,and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comprehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions.
文摘A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework of critical state soil mechanics and modified Cam-clay model. The existing model hasbeen generalized to simulate the experimentally observed behavior of unsaturated clays by introducingBishop＇s stress and suction as independent stress parameters and modifying the hardening rule and yieldcriterion to take into account the role of suction. Also, according to previous studies, an increase intemperature causes a reduction in specific volume. A reduction in suction （wetting） for a given confiningstress may induce an irreversible volumetric compression （collapse）. Thus an increase in suction （drying）raises a specific volume i.e. the movement of normal consolidation line （NCL） to higher values of voidratio. However, some experimental data confirm the assumption that this reduction is dependent on thestress level of soil element. A generalized approach considering the effect of stress level on themagnitude of clays thermal dependency in compression plane is proposed in this study. The number ofmodeling parameters is kept to a minimum, and they all have clear physical interpretations, to facilitatethe usefulness of model for practical applications. A step-by-step procedure used for parameter calibrationis also described. The model is finally evaluated using a comprehensive set of experimental datafor the thermo-mechanical behavior of unsaturated soils.2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
基金supported by Shenzhen(China)Science and Technology Innovation Committee(Grant Nos.JSGG20180504170449754)supported by Center for Computational Science and Engineering at Southern University of Science and Technology,Shenzhen,China。
文摘Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently developed SIMSAND critical state sand model combined with the smoothed particle hydrodynamics(SPH)method is adopted in this work to study slope failure under large deformations.To illustrate the efficiency and accuracy of the SIMSAND-SPH approach,a series of slope collapse studies using the discrete element method(DEM)considering various particle shapes(i.e.spherical,tetrahedral and elongated)is adopted as benchmarks.The parameters of the SIMSAND model are calibrated using DEM triaxial tests.In comparison to the DEM simulations,the runout distance and final slope height are well characterized with the SIMSAND-SPH approach with less computational cost.All comparisons show that the SIMSAND-SPH approach is highly efficient and accurate,which can be an alternative numerical tool to simulate real scale granular flow.
基金the Shenzhen Research and Technology Fund(No.JSGG20180504170449754)the grant from the Research Grants Council of the Hong Kong Special Administrative Region(No.UGC/FDS13/E06/18),China。
文摘The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for engineering design and practice.In this paper,we propose a novel numerical approach to study soil collapse involving large deformation.The approach combines a recently developed critical state-based sand model SIMSAND for describing complex sand mechanical behaviors,and the smoothed particle hydrodynamics(SPH)method for dealing with large deformation.To show the high efficiency and accuracy of the proposed approach,a series of column collapses using discrete element method(DEM)and considering the influence of particle shapes(i.e.spherical shape(SS),tetrahedral shape(TS),and elongated shape(ES))were adopted as benchmarks and simulated by the proposed method.The parameters of SIMSAND were calibrated from the results of DEM triaxial tests on the same samples.Compared with the results of DEM simulations and reference solutions derived by published collapse experiments,the runout distance and final height of specimens with different particle shapes simulated by SPH-SIMSAND were well characterized and incurred a lower computational cost.Comparisons showed that the novel SPH-SIMSAND approach is highly efficient and accurate for simulating collapse,and can be a useful numerical analytical tool for real scale engineering problems.
文摘Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years.A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand.Sand with 0%,0.2%,0.4%,and 1%fiber contents,prepared to yield random distribution,was sheared under several confining pressures and controlled via their initial relative densities.The test results showed that the maximum and residual deviatoric stresses increased,whereas the volumetric expansion decreased with an increase in fiber content.Although the stress ratio h(=q/p′)and specific volume changed depending on the fiber content and confining pressure with shear progression,they each reached the same values for a definite fiber content at the end of shearing,independent of initial relative density.In other words,the unique critical state line can be found for a definite fiber content.Moreover,the greater the fiber content,the larger the slope of the critical state line at the end of shearing.Additionally,as the length of fibers shortened with the same percentage of fiber inclusions in sand,the deviatoric stress and the stress ratio decreased,approaching the shear-strain-volumetric response of unreinforced sand.
基金financial support for Australian Academy of Science Early Career Fellowship(RI 18.6) in 2012-2013 from the Australia-India Strategic Research Fund (AISRF) to visit Department of Civil Engineering,Indian Institute of Science,Bangalore,India to work for the background studies of this paper
文摘There have been significant advances in the application of critical state,CS,in liquefaction potential assessment.This was done by comparing state parameter,j with estimated characteristic cyclic stress ratio,CSR due to an earthquake.A cyclic resistance ratio,CRR curve,which can be determined from cyclic liquefaction tests,separates historical liquefied and non-liquefied data points(j,CSR).On the other hand,the concepts of equivalent granular state parameter,j*,which was developed for sands with fines,can be used in lieu j to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines,irrespective of fines content(fc).The present work combines these two propositions,and by merely substituting j*for j into the aforementioned CS approach to capture the influence of fc.A series of static and cyclic triaxial tests were conducted,separately and independently of the concept of j*,for sand with up to fc of 30%.The clean sand was collected from Sabarmati river belt at Ahmedabad city in India which was severely affected during the Bhuj earthquake,2001.The experimental data gave a single relation for CRR and j*which was then used to assess liquefaction potential for a SPT based case study,where fc varies along the depth.The prediction matched with the field observation.
基金supported by the National Science Foundation of the United States under a research grant (CMMI-1917238)
文摘Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.
基金The financial support from Xi'an Jiaotong-Liverpool University(grant No.RDF 18-01-23,PGRS 1906002 and REF-20-01-01)is gratefully acknowledgedThe first and second authors would also like to appreciate the support by the Key Program Special Fund at Xi'an Jiaotong-Liverpool University(grant No.KSF-E-19).
文摘This paper investigates the strength and critical state(CS)behaviours of granular materials via DEM simulations of true triaxial drained tests under three different loading modes including constant b(in-termediate stress ratio)tests with constantσ'1(major principal stress),constant p(mean pressure)and constantσ'3(minor principal stress)respectively.To this end,a series of samples are generated with the same particle size distribution,and with the confining stresses ranging from 100 kPa to 900 kPa.The CS is achieved for all samples.Both the macroscopic behaviours and the microscopic behaviours are examined and compared considering different loading modes,confining stresses and intermediate stress ratios(b).The critical state lines(CSLs)are found to be unique and independent of the loading modes,but dependent on the b values.The CSLs with b=0 and b=1 form the two boundaries of CSLs respectively beyond which CSLs under all other b tests cannot go beyond.Six different strength criteria are examined and compared in terms of both peak and CS failures.The Mohr-Coulomb strength criterion is found to be only suitable for axisymmetric loading conditions.The Lade-Duncan criterion is only suitable for describing peak strengths,which is dependent on the loading modes and confining stresses.The Satake criterion and Matsuoka-Nakai criterion are the more appropriate strength criteria for describing CS failures,indicating that the CS values of both the Satake parameter and the Matsuoka-Nakai parameter describe an inherent property that characterizes the CS failure for a given type of soil.The CS mechanical coordination number is fitted by a curved line for a given b value,which is unique regardless of the loading modes.The peak and CS values of both major and minor principal fabric tensors decrease with increasing b values,while they increase with increasing b values for the intermediate principal fabric tensor.
基金Guangdong Major Project of Basic and Applied Basic Research,China(Grant No.2019B030302010)the National Natural Science Foundation of China(Grant Nos.52301212,52071222,52101191,52001219)+1 种基金the National Key Research and Development Program of China(Grant No.2021YFA0716302)Guangdong Basic and Applied Basic Research,China(Grant Nos.2022A1515010347,2020B1515130007).
文摘Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization and good magnetic softness(high permeability and low core loss).In this work,utilizing the order modulation strategy,a critical state in a FeSiBCCr amorphous soft magnetic composite(ASMC),consisting of massive crystal-like orders(CLOs,∼1 nm in size)with the feature ofα-Fe,is designed.This critical-state structure endows the amorphous powder with the enhanced ferromagnetic exchange interactions and the optimized magnetic domains with uniform orientation and fewer micro-vortex dots.Superior comprehensive soft magnetic properties at high frequency emerge in the ASMC,such as a high saturation magnetization(Ms)of 170 emu g^(-1)and effective permeability(µ_(e))of 65 combined with a core loss(Pcv)as low as 70 mW cm^(-3)(0.01 T,1 MHz).This study provides a new strategy for the development of high-frequency ASMCs,possessing suitable comprehensive soft magnetic performance to match the requirements of the modern magnetic devices used in the third-generation semiconductors and new energy fields.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.106112015CDJXY200008)China Scholarship Council(Grant No.201306710022)
文摘Particle breakage has a significant influence on the stress-strain and strength behavior of rockfill material.A breakage critical state theory(BCST)was proposed to describe the evolution of particle breakage.The breakage critical state line in the breakage critical state theory was correlated with the breakage factor,which was fundamentally different from that of the original critical state theory.A simple elastoplastic constitutive model was developed for rockfill in the frame of BCST.An associated flow rule was adopted in this model.Isotropic,contractive and distortional hardening rules were suggested in view of the particle breakage.It was observed that the proposed model could well represent the complex deformation behaviors of rockfill material,such as the strain hardening,post-peak strain softening,volumetric contraction,volumetric expansion,and particle breakage under different initial confining pressures.
基金The work presented in this paper was financially supported by the National Basic Research Program of China （973 Program, Grant No. 2013CB036304）, National Natural Science Foundation of China （Grant Nos. 51308408 and 11372228）, and Fundamental Research Funds for the Central Universities. The authors gratefully acknowl- edge the support provided by these fundings.
文摘The interface between soil and structure can be referred to as a soil-structure system, and its behavior plays an important role in many geotechnical engineering practices, In this study, results are presented from a series of monotonic direct shear tests performed on a sand-structure interface under constant normal stiffness using the discrete element method （DEM）. Strain localization and dilatancy behavior of the interface is carefully examined at both macroscopic and microscopic scales. The effects of soil initial relative density and normal stress on the interface shear behavior are also investigated, The results show that a shear band progressively develops along the structural surface as shear displacement increases. At large shear displacement a unique relationship between stress ratio and void ratio is reached in the shear band for a certain normal stress, indicating that a critical state exists in the shear band. It is also found that the thickness and void ratio of the shear band at the critical state decreases with increasing normal stress. Comparison of the DEM simulation results with experimental results provides insight into the shear behavior of a sand-structure interface and offers a means for quantitative modeling of such interfaces based on the critical state soil mechanics.
基金The financial supports provided by Xi'an Jiaotong-Liverpool University(Grant Nos.RDF 14-02-44,RDF 15-01-38,RDF 18-01-23 and PGRS1906002)the Key Program Special Fund at XJTLU(Grant No.KSF-E-19)Natural Science Foundation of Jiangsu Province(Grant No.BK20160393)are gratefully acknowledged.
文摘The critical state soil mechanics(CSSM)framework has been widely used across a range of problems in geomechanics involving complex loading conditions.However,the uniqueness of the critical state has been disputed for many years and it remains a controversial issue.Motivated by previous investigations,a series of discrete element method(DEM)simulations were performed under both axial compression(AC)and axial extension(AE)stress paths.All samples were isotropically compressed at varying mean normal effective stresses(confining pressures)and sheared to a large axial strain of approximately 60%.It is found that there exist unique values of critical void ratios and stress ratios under critical state,which are independent of the samples’initial packings but dependent on stress paths.And the critical strength(stress ratio)for the AC stress path tests is higher than that for the AE stress path.The critical state lines(CSLs)are found to path-dependent but unique for each stress path.A unique linear relationship between the critical coordination numbers and critical void ratios is identified under the AC and AE stress paths respectively,but such a relationship depends on the stress paths.It is also found that there exist unique values of microscopic parameters in terms of deviator fabric under critical state,which are independent of the samples’initial packings but dependent on stress paths.All these simulation results lead to the conclusion of non-uniqueness of CSLs from both macroscopic and microscopic viewpoints.
基金The financial support from Xi'an Jiaotong-Liverpool University(grant Nos.RDF 18-01-23,PGRS1906002 and REF-20-01-01)is gratefully acknowledged。
文摘The present study investigates the critical state behaviour of granular assemblies composed of clumped particles under four different drained axisymmetric triaxial stress paths,using the discrete element method(DEM).A series of numerical samples were prepared at initial states with different density indexes(1D)and different initial confining pressures(ρ′0).These samples were sheared to large strains,at which constant stresses and volumes were maintained to reach the critical state.The evolution of stress ratio under the same loading mode(for the same intermediate principal stress ratio,b)is shown to yield an almost identical behaviour independent of stress paths,whereas the stress-strain response depends on the stress paths.Four different axisymmetric stress paths all share the same unique friction angle at critical state,indicating the Mohr-Coulomb failure criterion is the appropriate critical state strength criterion,which is at least true for the axisymmetric stress conditions.A unique coordination number(CN)is achieved at the critical state for a given po,which is independent of the stress path.The critical state CN is found to increase with the increase in po,which could be attributed to the decrease in the critical state void ratio(ec)as mean effective stress(ρ′0)increases.Interestingly,a unique linear functional relationship is found between the critical state values of cN and ec,and a unique polynomial functional relationship is found between the critical state values of CN andρ′.These functional relationships indicate no dependency on the stress paths or loading modes,thus characterizing unique features at critical states at both macroscopic and microscopic levels for a given type of granular material.
文摘Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.
基金supported by grants funded by the Hong Kong Research Grants Council(Grant No.CRF/C6006-20G)a grant provided by the Joint NSFC/RGC Joint Research Scheme(Grant No.N_HKUST603/22)the Fundamental Research Funds for the Central Universities(Grant No.Z1090125018).
文摘The effectiveness of using vegetation to stabilise shallow soil slopes heavily depends on the survival of vegetation,yet the amplification of extreme events induced by climate change threatens the health of plants covering slopes.Hydrochar is an environmentally friendly soil amender that can achieve the potential benefits of promoting plant growth for slope stabilisation and facilitation of waste upcycling.The mechanism underlying the hydrochar effects on the mechanical behaviour of unsaturated soils remains unclear.This study investigated the influence of grass-derived hydrochar on the water retention,compressibility,and shear strength of a compacted siltyeclay sand.Soil microstructural changes due to hydrochar amendment were measured to explain the soilehydrochar hydromechanical interaction.The increase in suction resulted in a less significant increase in yield stress and a negligible reduction in compressibility of the hydrochar-amended soil compared with the unamended case.This phenomenon was observed because hydrochar addition reduced the large pores with diameters greater than the macropore peak of 60 mm due to pore filling by hydrochar particles,resulting in a less substantial volume contraction during drying.Hydrochar introduced more significant effects on the soil’s shear strength in an unsaturated state compared to a saturated case.Despite the similarity of the unsaturated amended soil with the critical-state friction angle to the saturated case,the former exhibited a greater shear strength because the hydrochar addition improved water retention capability.As a result,the degree of saturation and,hence,Bishop’s effective stress were higher than those for the unamended case for a given suction.
基金jointly supported by the Science Fund for Distinguished Young Scholars of Hunan Province,China(Grant No.2024JJ2073)the National Natural Science Foundation of China(Grant No.52178443)the Fundamental Research Funds for the Central Universities of Central South University,China(Grant No.2022ZZTS0620)。
文摘This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique(ATT).Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio,matric suction,and confining pressure on the properties of CREFMs.Key findings reveal a primary suction range of 0 e100 kPa characterized by hysteresis,which intensifies with decreasing density.Notably,the air entry value and residual suction are influenced by void ratio,with higher void ratios leading to decreased air entry values and residual suctions,underscoring the critical role of void ratio in hydraulic behavior.Additionally,the critical state line(CSL)in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction,significantly affecting dilatancy and critical states.Furthermore,the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction.A novel modified dilatancy equation was proposed,which enhances the predictability of CREFMs'responses under variable loading,particularly at high stress ratios defined by the deviatoric stress over the mean effective stress.This research advances the understanding of CREFMs'performance,especially under fluctuating environmental conditions that alter suction levels.
