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This paper investigates shear banding as a possible failure mode for silt–clay transition soils under general three-dimensional stress conditions. Drained and undrained true triaxial tests with constant b values were performed on tall prismatic specimens of such soils with systematically varying silt contents. Based on the values of critical plastic hardening modulus, shear banding does not govern the strength characteristics of the soils for b values less than 0.2. For larger b values, shear band formation is essentially critical as it takes place in the hardening regime of the stress–strain curves prior to the smooth peak failure points. An increase in silt content appears to move the onset of shear banding to lower levels of shear in the stress–strain relations of the silt–clay transition soils. It is also demonstrated that a non-associated constitutive model with a single hardening law is capable of accurately predicting the onset of shear banding in normally consolidated silt–clay transition soils based on bifurcation theory.

The structure of unsaturated loess has a significant impact on its hydraulic and mechanical properties. An elastoplastic model considering the structured evolution of unsaturated loess is presented in this paper using double stress variables consisting of average skeleton stress and suction. The model divides the structure of unsaturated loess into inherent structure and suction-induced structure from the structured composition of loess and gives isotropic compression equation for unsaturated loess that considers the structure evolution. At the same time, a soil–water characteristic curve considering the influence of the void ratio is introduced to reflect the coupling between the hydro-mechanical behaviours of unsaturated loess. The proposed isotropic compression equation is extended to axisymmetric stress space with the aid of the yield surface and flow law in the modified Cam-clay model. The proposed model can not only reflect the structured evolution of loess, but also predict reasonably the mechanical and hydraulic behaviour of loess under different stress paths. The reasonableness and availability of the proposed model are initially verified by comparison with the results of the unsaturated loess isotropic compression tests at constant suctions, the wetting test at constant net stresses, the complex stress path tests and the triaxial shear tests as well. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Slope stability analysis is the earliest subject that classical soil mechanics tried to solve but has not yet been satisfactorily solved. Various stability analysis methods are roughly equivalent at home and abroad, while the current numerical analysis methods can generally only obtain slope stress, displacement, and plastic zone cannot obtain slope dangerous sliding surfaces and corresponding safety factor. With the development of computer technology, especially the development of nonlinear elastoplastic finite element calculation technology for geotechnical materials, the finite element strength reduction method has attracted attention in recent years. In this paper, the finite element strength reduction method is used to search for the dangerous sliding surface of the slope to obtain the corresponding stability safety factor, and the slope of Fushun West Open-Pit Mine in China is used as an example to analyze the calculation.

According to post-seismic observations, spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction, where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a “liquid”. Therefore, correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field. In advanced elastoplastic models of sand liquefaction, certain fitting parameters have a remarkable effect on the computed results. However, the identification of these parameters, based on the experimental data, is usually intractable and sometimes follows a subjective trial-and-error procedure. For this, this paper presented a novel calibration methodology based on an optimization algorithm (particle swarm optimization (PSO)) for an advanced elastoplastic constitutive model. A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations. To overcome computational problem probably appearing in simulation of the cyclic triaxial test, two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions. The Dafalias model has been used as an example to demonstrate the main programme. With the calibrated parameters for the HN31 sand, the computed results were highly consistent with the laboratory experiments (including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes). Finally, an extension example is given for Ottawa sand F65, suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.

In the ultra‐deep reservoir or other deep‐buried subsurface engineering, the in situ stress is high enough to make the rock transition from the brittle to the plastic. In such situation, the fracturing process always goes with the plastic deformation together. Therefore, to develop an elastoplastic constitutive model which can simultaneously account for both fracture and plastic deformation is critically important. In this paper, an elastoplastic augmented virtual internal bond (EP‐AVIB) model is developed. In EP‐AVIB, a hyperelastic AVIB is developed to characterize the elastic deformation of rock, in which the micro bond is linear elastic in compression whereas is hyperelastic in tension. The Drucker‐Prager yield criterion is employed to characterize the plastic deformation. Thus, the EP‐AVIB can combine the fracture and plastic deformation together. The simulation examples show that the EP‐AVIB can simulate the elastoplastic mechanical behaviors and the fracturing process of rock subjected to compression. It provides a simple approach to the elastoplastic failure simulation of rock. Its perspective in deep reservoir and deep‐buried subsurface engineering simulation should be inspiring. [ABSTRACT FROM AUTHOR]

In order to investigate the hydromechanical behavior of basalt in Baihetan hydropower station in China, a series of uniaxial and triaxial hydromechanical tests were carried out in the laboratory. Experimental results indicated that the deformation state of samples transformed from compaction to dilation. Characteristic stresses were determined by a moving point regression technique, including the crack closure stress σ cc , crack initiation stress σ ci , crack damage stress σ cd , and peak stress σ p , revealing a strong dependence on the confining and pore pressures. Failure modes of the basalt changed from tensile to tensile-shear failure as the confining pressure increased. Moreover, scanning electron microscope (SEM) tests demonstrated that the growth of microcracks caused the failure of the basalt. Based on the experimental results, an elastoplastic constitutive model was proposed to take into account the hardening and softening, as well as the hydro-mechanical behavior of basalt. The return mapping algorithms of the elastoplastic constitutive model are deduced for plastic corrections. Model parameters were determined by experimental results. Finally, the validity of the model was demonstrated by comparing the experimental results with the simulated curves. [ABSTRACT FROM AUTHOR]

The advantages of data science have inspired the development of data-driven approaches for solving constitutive modeling problems, which have become a new research focus in engineering mechanics. These approaches help fully utilize the information inherent in the data, bypassing the traditional modeling processes. In order to advance the development of Constitutive Model Based on Data-Driven (CMBDD), we introduced a novel framework called the Geometric Physical I nformation-enhanced D ata- D riven E lasto P lastic constitutive model (IDD-EP) under hysteretic loading paths. IDD-EP adopts an "Encoder-Decoder" framework, with the information transmission between the encoder and decoder facilitated by the "Geometric Physical Information" proposed in this paper. Specifically, IDD-EP-I, serving as the encoder, extracts Geometric Physical Information from experimental constitutive images, which is then transmitted to the modular data-driven decoder IDD-EP-II, designed based on physical mechanisms, to compute material responses under arbitrary paths. IDD-EP aims to establish a constitutive model relying solely on a single small sample without using deep learning techniques and avoids the challenge of model parameter fitting in classical models through a non-mathematical model design. In addition to discussing the general framework of IDD-EP, this paper specifically demonstrates a specialized version of the IDD-EP framework based on uniaxial buckling-restrained braces (BRBs), which are commonly used in structural vibration control, in order to showcase a specific implementation example of the IDD-EP model. The IDD-EP method in this paper accurately predicts the mechanical response of the BRB using only one constitutive experimental image, without the need to pre-select a base constitutive model or fit model parameters. This innovative approach to IDD-EP opens a new avenue for constitutive modeling of elastoplastic materials and may offer solutions to a wider range of history-dependent constitutive modeling challenges in the future. [ABSTRACT FROM AUTHOR]

This paper investigates shear banding as a possible failure mode for silt–clay transition soils under general three-dimensional stress conditions. Drained and undrained true triaxial tests with constant b values were performed on tall prismatic specimens of such soils with systematically varying silt contents. Based on the values of critical plastic hardening modulus, shear banding does not govern the strength characteristics of the soils for b values less than 0.2. For larger b values, shear band formation is essentially critical as it takes place in the hardening regime of the stress–strain curves prior to the smooth peak failure points. An increase in silt content appears to move the onset of shear banding to lower levels of shear in the stress–strain relations of the silt–clay transition soils. It is also demonstrated that a non-associated constitutive model with a single hardening law is capable of accurately predicting the onset of shear banding in normally consolidated silt–clay transition soils based on bifurcation theory. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The contact behavior of hemisphere pressed by a rigid flat is analyzed based on the finite element method under the condition of independent varying elastic moduli (E) and yield strengths (Y). The contact behavior is related to the ratio of E/Y. The mean contact pressure (p*) first increases and then decreases with the increasing interference, and this trend is more obvious for the contact of materials with the comparatively small ratio of E/Y. The end of the elastoplastic range or the inception of the fully plastic range is determined according to the interference corresponding to the peak value of the p*. The contact load and area in elastoplastic and fully plastic ranges are determined by the interference and the ratio of E/Y. Then, a new contact model to accurately predict the contact load and area for a wide range of E and Y is proposed, and compared with the previous models. The correctness of the current model is verified by the experimental measurement results recorded in previous literature. [ABSTRACT FROM AUTHOR]

In the framework of generalized plasticity theory, this paper presents a new elastoplastic model to characterize complicated softening/hardening and dilation/contraction behaviors of sand–gravel composites in triaxial tests. The model has six parameters that are determined by the conventional triaxial test directly, which is of great practical interest to engineers. The dilatancy equation that is able to describe the dilatancy of sand–gravel composites during the whole shearing process is incorporated into the model. The advantage of the proposed model in predicting the dilatancy behavior of sand–gravel composites is demonstrated by comparing it with three widely used dilatancy equations. A set of drained triaxial compression tests were launched to examine the performance of the proposed model. In addition, the applicability of the model is also confirmed by sand–gravel composites tests covering a wider range of confining pressure in previous literature. The generality of the model on other granular materials including rockfill, Ottawa sand, calcareous sand, cement-sand–gravel material, and glass beads mixtures is also verified by comparing the experimental results with the corresponding fitting results. Furthermore, the proposed model is programmed into the nonlinear finite element program GEODYNA and applied to the numerical simulation of high concrete-faced sand–gravel dams. Summarizing the fitting and numerical results comprehensively, the constitutive model proposed in this study is capable of characterizing the mechanical behaviors of granular materials and can provide a powerful tool for geotechnical engineering. [ABSTRACT FROM AUTHOR]

Considering unsaturated triaxial tests including a ceramic disk as initial and boundary value problems, a series of suction change, isotropic consolidation, and drained shearing processes was simulated using a soil-water-air coupled elastoplastic finite deformation analysis code. As a result, it was demonstrated that the delayed behavior of a wetting-induced collapse during the suction change and isotropic consolidation processes, as well as water-absorption behavior during the subsequent drained shearing process, were attributed not to the characteristics of the soil specimen, but to the permeability of the disk. Thus, it is important to take the ceramic disk into account in unsaturated triaxial tests regarded as initial and boundary value problems in order to understand the temporal change behavior of unsaturated soil specimens. Otherwise, there is a risk that the behavior appearing as the solution of an initial and boundary value problem may be modeled as a constitutive relation.

The purpose of this study is to establish an elastic–plastic damage constitutive model of shale and simulate the elastic–plastic damage characteristics of shale under stress. Based on the unified strength theory and the mechanics of shale rock samples characterized in laboratory tests, a new elastic–plastic damage constitutive model for shale is established by introducing compression factors and damage variables. The main considerations include the compressibility of primary fractures and pores in the shale core, and the formation of secondary cracks in the rock matrix under stress. A fully implicit backward Euler regression mapping algorithm has been used to solve the model, and the numerical simulation results are in good agreement with the experimental results. The results show that the model established in this paper can accurately simulate the elastic–plastic damage characteristics of shale under stress, and that it provides a new numerical simulation method for describing the elastic–plastic damage in shale.

Austenitic stainless steel is useful for storing and transporting liquefied natural gas (LNG) at temperatures below −163 °C due to its superior low-temperature applications. This study develops a computational method for the failure prediction of 304L stainless steel sheet to utilize its usability as a design code for industrial purposes. To consider material degradation in a phenomenological way during the numerical calculation, the combined Swift–Voce equation was adopted to describe the nonlinear constitutive behavior beyond ultimate tensile strength. Due to the stress state-dependent fracture characteristics of ductile metal, a modified Mohr–Coulomb fracture criterion was adopted using stress triaxiality and Lode angle parameter. The numerical formulation of the elastoplastic-damage coupled constitutive model with fracture locus was implemented in the ABAQUS user-defined subroutine UMAT. To identify the material and damage parameters of constitutive models, a series of material tests were conducted considering various stress states. It has been verified that the numerical simulation results obtained by the proposed failure prediction methodology show good agreement with the experimental results for plastic behavior and fractured configuration. [ABSTRACT FROM AUTHOR]

In this paper, an elastoplastic constitutive model is proposed to uniformly describe the mechanical behavior of cemented/ non-cemented soil under different loading conditions. A state variable characterizing the degree of cementation is introduced into the yield function of the cyclic mobility model, and an evolution rule is proposed to describe the degradation of cementation and structure. Since the cyclic mobility model is developed based on the concepts of subloading surface and superloading surface, the newly proposed model inherits both its advantages and can systematically describe the effects of cementation, structure, overconsolidation, and stress-induced anisotropy on the mechanical behavior of soil. Compared with cyclic mobility model, this proposed model adds only one state variable associated with cementation, which has clear physical meaning and can be determined by uniaxial compression or tension test. The capability of the proposed model has been validated carefully through a series of tests such as isotropic, uniaxial, and triaxial tests under monotonic and cyclic loading conditions. [ABSTRACT FROM AUTHOR]

Due to the degradation of the elastic modulus and Poisson's ratio, hard brittle rock is characterized as non-linear mechanical properties. Elastic modulus, Poisson's ratio, and strength parameters show non-linear characteristics with increase of confining pressure, due to the microcracks in hard brittle. The pre-peak deformation process of rock is divided into four stages based on the variation of microcracks to characterize the asymptotic deformation process of rock. The variation of elastic modulus, Poisson's ratio, and strength parameters with confining pressure are acquired in different stages. The results show that the elastic modulus E is not only related to the confining pressure, but also related to the deformation and damage state of the rock; in addition, the deformation and damage state of the rock depends on the activity state of the microcracks. The elastic modulus at each stage increased significantly with the increase of the confining pressure. The Poisson's ratio v of the rock samples under different confining pressures at the same deformation stage is relatively close and approximately constant. On this basis, an elasto-brittle-plastic constitutive model reflecting the non-linear mechanical characteristics of hard brittle rock before the peak is established. The model is composed of non-linear elastic stage, strain softening stage, and plastic flow ones, which is applied to numerically simulate hard brittle rocks under different confining pressures, and the obtained stress–strain curves are consistent with the test curves, reflecting the pre-peak nonlinear mechanical behavior of hard brittle rocks. This study will be conducive to deformation, stability analysis, and engineering design of deep roadway and tunnel under high in-situ stress. [ABSTRACT FROM AUTHOR]

This study deals with the problem of axial and radial swelling of a cylindrical bentonite specimen with a gap at the top or side. Unsaturated soil water coupled finite element analyses are carried out to analyze how the bentonite specimen changes during the process of swelling due to water absorption from the surface facing the gap. The behavior of the bentonite after the finite gap is filled by the swollen bentonite until the equilibrium state is also analytically evaluated. The analysis results show that the distribution of void ratio and swelling pressure in the specimen remains non-uniform in both axial and radial swelling, even if the bentonite specimen reaches a saturated and equilibrium state. In the case of axial swelling, the radial and hoop stresses remain equal at all positions in the specimen, whereas in the case of radial swelling, an anisotropic stress state, in which even the radial and hoop stresses are different, is observed immediately after the start of water absorption, resulting in the formation of complex stress distribution in the radial direction. [ABSTRACT FROM AUTHOR]

To achieve versatility, a unified nonlinear strength (UNS) criterion is put forward for capturing the complicated strength behaviors exhibited by geomaterials under three dimensional (3D) stress paths. The UNS criterion, widely covering meridian planes and octahedral planes, can serve for describing the nonlinear strength behaviors exhibited by soils, as well as confirm how the intermediate principal stress affects the strength of different materials. Based on UNS strength criterion, an elastoplastic constitutive model is presented, with the purpose of predicting the strength as well as deformation behavior exhibited by soils under 3D stress conditions. Besides, although the proposed model is extremely simple, it is fit for predicting the results of true triaxial tests in related literature with the help of the UNS criterion, and meanwhile can confirm how intermediate principal stress affects material strength and material deformation when the stresses are different.

A series of triaxial compression tests of frozen sandy soil are carried out under five confining pressures (1 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa) at –6 °C. By comparing the grain size distribution curves of frozen sandy soil before and after shearing, it is found that significant particle breakage can occur during triaxial shearing. Particle breakage changes internal structure of geomaterials and has a significant effect on their stress–strain relationships. In order to accurately describe the effect of particle breakage of frozen sandy soil on the stress–strain relationships, an elastoplastic constitutive model for frozen sandy soil considering particle breakage is proposed. Based on the energy balance equation established by Indraratna and Salim, the constant critical state stress ratio (Mcr) in the energy balance equation is modified to the stress ratio (M) which changed with shear strain during the shearing process. A yield function, considering particle breakage, is proposed using the modified energy balance equation. The hardening law is determined based on the rebound test results of frozen sandy soil, and the associated flow rule is adopted in the model. Compared with experimental data, the model can well simulate the stress–strain relationships under different confining pressures for frozen sandy soil. The particle breakage characteristics of frozen sandy soil are studied. The energy balance equation considering particle breakage is modified to calculate the energy dissipation of frozen sandy soil. An elastoplastic constitutive model for frozen sandy soil considering particle breakage is proposed. [ABSTRACT FROM AUTHOR]

The risk assessment of liquefaction damage is crucial for recovery from large-scale earthquakes, which are predicted to occur in recent years. In this study, the liquefaction risk is evaluated over a wide area through effective stress analysis, considering the interaction between the soil particles and pore water. The target area of the analysis was the 23 wards of Tokyo, including the zero-meter zone, and a 3D ground model was constructed from the borehole data. A vertical columnar ground model is established at 463 locations from the 3D ground model using the material parameter determination flow. The liquefaction risk of a wide area is evaluated by performing seismic response analysis using two types of earthquake motions for each analysis point, thus showing the difference in the risk and degree of liquefaction by location. In the future, various dynamic analyses must be conducted with sufficient resolution and compared with the actual damages. [ABSTRACT FROM AUTHOR]

Recently, the occurrence of large earthquakes has become a concern in Japan, prompting the need for a numerical method that can accurately predict real phenomena, such as the elastoplastic soil-water coupled finite element method. Because the elastoplastic constitutive model requires many material parameters, various soil tests and specialized knowledge are needed to determine these material parameters. In this study, a new method was proposed to determine the material parameters from the limited ground information obtained by borehole inspections and the method was validated by comparing the numerical results with monitored seismic behavior. One-dimensional seismic analyses were conducted using the material parameters estimated from borehole data near the target sites. It was confirmed that the amplitude and predominant period obtained by numerical simulation were consistent with the monitored data. As a result, it was found that the dynamic numerical result was more consistent with the monitored data when the compression index was set to be larger than that in the static analysis. [ABSTRACT FROM AUTHOR]

Considering unsaturated triaxial tests including a ceramic disk as initial and boundary value problems, a series of suction change, isotropic consolidation, and drained shearing processes was simulated using a soil-water-air coupled elastoplastic finite deformation analysis code. As a result, it was demonstrated that the delayed behavior of a wetting-induced collapse during the suction change and isotropic consolidation processes, as well as water-absorption behavior during the subsequent drained shearing process, were attributed not to the characteristics of the soil specimen, but to the permeability of the disk. Thus, it is important to take the ceramic disk into account in unsaturated triaxial tests regarded as initial and boundary value problems in order to understand the temporal change behavior of unsaturated soil specimens. Otherwise, there is a risk that the behavior appearing as the solution of an initial and boundary value problem may be modeled as a constitutive relation. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel is useful for storing and transporting liquefied natural gas (LNG) at temperatures below −163 °C due to its superior low-temperature applications. This study develops a computational method for the failure prediction of 304L stainless steel sheet to utilize its usability as a design code for industrial purposes. To consider material degradation in a phenomenological way during the numerical calculation, the combined Swift–Voce equation was adopted to describe the nonlinear constitutive behavior beyond ultimate tensile strength. Due to the stress state-dependent fracture characteristics of ductile metal, a modified Mohr–Coulomb fracture criterion was adopted using stress triaxiality and Lode angle parameter. The numerical formulation of the elastoplastic-damage coupled constitutive model with fracture locus was implemented in the ABAQUS user-defined subroutine UMAT. To identify the material and damage parameters of constitutive models, a series of material tests were conducted considering various stress states. It has been verified that the numerical simulation results obtained by the proposed failure prediction methodology show good agreement with the experimental results for plastic behavior and fractured configuration.

Triaxial tests and numerical simulations were conducted to determine the water absorption compression of unsaturated soil. In the triaxial tests, unsaturated silt specimens under the same initial condition were prepared and the processes of different suction reduction, isotropic consolidation, and exhausted-drained shearing were applied to the specimens. The numerical simulations used a soil-water-air coupled finite deformation analysis code with a newly incorporated elastoplastic constitutive model. The degree of saturation was introduced to the internal state variables of the yield function of the SYS Cam-clay model and a soil-water characteristic model with void ratio dependency. Then, the triaxial test was treated as an initial and boundary value problem, and the series of processes in the experiments were simulated using a single set of material constants and initial values. The new findings are as follows: 1) The loading criterion and the classification of loading conditions considering change in saturation degree can be specified in the elastoplastic constitutive model for unsaturated soil. 2) Water absorption compression behavior was observed in the experiments not only under suction reduction but also under constant suction condition. This water absorption compression under constant suction condition was explained as a saturation-increase behavior due to volume compression using the soil-water characteristic model with void ratio dependency. 3) By considering the triaxial test as an initial and boundary value problem, the temporal change in the volume and the amount of water absorption/drainage were able to be reproduced. [ABSTRACT FROM AUTHOR]

In this paper, the stress–strain responses of frozen sands and an elastoplastic constitutive model based on the homogenization theory of heterogeneous materials are presented. In the model, frozen soils are conceptualized as binary-medium materials consisting of bonded blocks and weak bands, and their mechanical behavior is described with elastic–brittle and elastoplastic constitutive models, respectively. By introducing two groups of parameters (i.e., the breakage ratio (λv and λs) and strain concentration coefficient (cv and cs) related to the spherical and deviatoric stress components), the proposed model incorporates the breakage process of ice crystals and nonuniform strain distributions between the matrix (bonded elements) and inclusions (frictional elements) of the heterogeneous frozen soil samples. Moreover, an elasticity-based model and a double hardening constitutive model are employed to simulate the mechanical properties of the bonded elements and the characteristics of the frictional elements, respectively. To provide appropriate and quantitative predictions with the binary-medium constitutive model proposed here, triaxial compression tests are performed on the frozen and unfrozen sands to determine the individual parameters at confining pressures of 300–1800 kPa. The model validations demonstrate that the predictions agree well with the available laboratory results. [ABSTRACT FROM AUTHOR]

The liquefaction of gravelly soil has been demonstrated in many earthquakes, but the constitutive model to predict its liquefaction behavior is limited. The dilatancy equation plays an important role in establishing elastoplastic models of geotechnical materials. Recognizing the unique dilatancy characteristics of gravelly soil, this study introduces an improved nonlinear dilatancy equation into the generalized plasticity model. Consequently, a unified elastoplastic constitutive model is proposed, aimed at accurately predicting both the monotonic and cyclic behaviors of saturated gravelly soil under diverse drainage conditions. A series of drained and undrained triaxial tests of gravelly soil under monotonic and cyclic loadings are carried out to validate the model performance. In addition, the model performance is also examined through monotonic and liquefaction tests of gravelly soil obtained from prior publications. Furthermore, the proposed model is implemented into the nonlinear finite element program GEODYNA and applied to the numerical simulation of the Kobe Port Island liquefaction to better validate the capabilities of the proposed model. From the comprehensive analysis of triaxial tests and numerical simulations, the proposed model performs well in predicting mechanical behavior of gravelly soil and can provide a powerful tool for seismic liquefaction analysis of gravelly soil sites. [ABSTRACT FROM AUTHOR]

• Thermo-elastoplastic constitutive model of soil is adopted. • Thermal-induced equivalent stress tensor. • Effect of temperature on the pre-consolidation stress and critical stress ratio is considered. • Thermal-hardening and thermal-softening behavior of soils can be described properly. Based on the modified Cam-clay model and the concept of subloading yield surface, a thermo-elastoplastic model of normally consolidated and overconsolidated soils is presented in detail. The model is able to describe the thermal-hardening and thermal-softening mechanical behavior of soils with a unified set of parameters. A thermo-induced equivalent stress is proposed to consider the effect of temperature on yield surface and evolution of overconsolidation during shearing process. At the same time, the effect of temperature on the shear stress ratio at the critical state is also implemented in the model. Through comparing the simulated results with test results under different loading and temperature conditions, the availability and the accuracy of the proposed model are carefully verified. Finally, the generating mechanism of the thermal-hardening and thermal-softening mechanical behavior of soil under non-isothermal condition is discussed based on the proposed model. [ABSTRACT FROM AUTHOR]

Geothermal energy is renewable, clean and green energy generated and stored in the Earth's crust. The most important consideration for geothermal energy development in non-hydrothermal scenarios is the use of hydraulic fracturing technology to establish an effective network pathway to conduct fluid from injectors to producers. Hydraulic fracturing in geothermal wells is referred to as hydro-shearing and the aim is to improve the conductivity of natural fractures. In this paper, linear elastic constitutive relationships and shear strength of discontinuities in the pre-peak region are initially considered. Based on the dynamic frictional weakening, a proved conductive aperture and the post-peak elastoplastic constitutive models are proposed to analyze the deformation and conductivity of the natural fracture. Simulation research has shown that the joint compressive strength (JCS) mainly affects the shear displacement and hardly affects the dilation. The joint roughness coefficient (JRC) is more important for decreasing the shear strength and improves the dilation aperture. To no one's surprise, reducing the effective normal stress is the best way for increasing the shear displacement, dilation and conductivity of the natural fracture. Almost 90% of the slip displacement and dilation occurs after fracture shear failure. This displacement not only increases the hydraulic conductivity of the fracture, but also reduces the required surface pumping pressure. [ABSTRACT FROM AUTHOR]

This study presents a sophisticated elastoplastic constitutive model for unsaturated soil using Bishop-type skeleton stress and degree of saturation as state variables in the framework of critical state soil mechanism. The model is proposed in order to describe the coupled hydromechanical behavior of unsaturated soil irrespective of what kind of the loadings or the drainage conditions may be. At the same time, a water retention characteristic curve considering the influence of deformation on degree of saturation is also proposed. In the model, the superloading and subloading concepts are introduced to consider the influences of overconsolidation and structure on deformation and strength of soils. The proposed model only employs nine parameters, among which five parameters are the same as those used in Cam-Clay model. The other four parameters have the clear physical meanings and can be easily determined by conventional soil tests. The capability and accuracy of the proposed model have been validated carefully through a series of laboratory tests such as isotropic loading tests and triaxial monotonic and cyclic compression tests under different mechanical and hydraulic conditions. [ABSTRACT FROM AUTHOR]

The study is devoted to the strength and deformation behavior of fine-grained sandstone. A series of triaxial compression tests were conducted on rock samples under various confining pressures (3, 5, 10, 15, and 20 MPa) in the laboratory. The experimental results showed that the nonlinear behavior and plastic deformation of the sandstone are prominent during loading process. The peak strength of the sandstone can be enhanced with the increase of the confining pressure. The initial yield stresses σy are approximately 87.2%, 80.2%, 62.1%, 75.2%, and 83.8% of the peak strengths σp, respectively. The shear failure is predominated failure mode under different confining pressures. Based on experimental results, an elastoplastic model is proposed using a linear yield function in p-q plane, as well as a non-associated plastic potential function. Furthermore, the numerical formulations of a return mapping algorithm for constitutive model implementation are introduced in this work. The numerical results agree well with the experimental data, which show that this model is able to describe the elastoplastic behavior of the sandstone under triaxial compression. [ABSTRACT FROM AUTHOR]

This paper proposes a new constitutive model for geotechnical materials that consists two basic constitutive functions, the free energy function and the dissipation rate function, within the framework of hyperplastic theory. This free energy function is capable of describing the pressure-dependent elastic behavior of soils. The new constructed dissipation rate function accounts for the frictional mechanism of energy dissipation. Based on this dissipation rate function, the non-associated flow rule can be obtained. Furthermore, the convexity of the yield surface that is derived from the dissipation rate function is proved. Predictions of the behavior of a soil sample using this new constitutive model agree well with triaxial test data under drained and undrained conditions. [ABSTRACT FROM AUTHOR]

The interaction between sloping marine structure and level ice is a complex process, which contains local crushing and flexural failure. The ice fragments fallen from ice sheet will continuously experience rotation, sliding and accumulation processes. These processes interfere with each other and give rise to difficulty to determine accurately the ice loads on structure. The issue is solved by using cohesive element model (CEM) in this paper. In the condition of a cone icebreaking against level ice, the elastoplastic linear softening constitutive model is introduced to the regular tri-prism bulk elements to present the microscopic crushing of ice sheet, while the bending failure of ice sheet is caused by the failure of cohesive elements. The proposed models are incorporated into the LS-DYNA finite element code. The mesh dependency study and a series of parametric analysis on the main parameters of models are conducted. The numerical results are compared with available model test data in literature, and good agreements are achieved. Then a series of simulations in terms of invasion velocity, cone angle and cone waterline diameter are performed. Effects of these parameters on the ice loads and contributions of breaking module are discussed. [ABSTRACT FROM AUTHOR]

Soils encountered in geotechnical engineering exhibit a certain degree of overconsolidation and are in a three-dimensional (3D) stress state. The overconsolidated ratio (OCR) and the intermediate principal stress play a significant role in the strength and deformation of overconsolidated soils. By considering the variation of the peak stress ratio with OCR, and taking the zero-tension line and the critical state line as asymptotes, a continuous and smooth Hvorslev envelope is deduced to describe the peak strength of overconsolidated soils. Based on the proposed Hvorslev envelope, a simple 3D elastoplastic constitutive model for overconsolidated soils is directly established through the characteristic stress method. The constitutive relation of the proposed model is presented by the calculation of the total strain increment. All material parameters have clear physical meanings and can be determined by conventional laboratory tests. The isotropic compression path, the triaxial drained shearing path with constant p , the triaxial undrained shearing path, and the true triaxial drained shearing path with constant p and θ are adopted to demonstrate the essential features of the proposed model. The effectiveness of the proposed model is confirmed by comparing the experimental data from Lower Cromer till, Kaolin clay, and Fujinomori clay with corresponding model predictions. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for the development of an elastoplastic constitutive model to predict the strength and deformation behaviour of soils under general stress conditions. The proposed approach was based on characteristic stress, which considers the effect of the intermediate principal stress on the material strength. Referring to the Cam-clay model, the shear dilatancy equation, plastic potential function and hardening parameter for the developed model were all derived using the characteristic stress. The model predictions indicated that the established model could quantitatively reproduce the negative dilatancy behaviour, positive dilatancy behaviour, and three-dimensional strength properties of soils. [ABSTRACT FROM AUTHOR]

Soil turning is an infrastructure activity in the field of geotechnical engineering. In this study, we propose a new soil turning numerical model based on the Smoothed Particle Hydrodynamics (SPH) method, in which an elastoplastic constitutive model is implemented. To validate the model, firstly, a landslide benchmark test is studied, the error of the maximum sliding distance is only 1.5 % compared to the experimental data. Next, a combined experimental numerical investigation on the soil turning process is carried out. We compare the experimental observations with the numerical modeling results and find that the numerical error of the peak height and the horizontal distance of the soil is about 2.56 % and 3.37 %, respectively, indicating that the proposed SPH model can reproduce the soil turning process accurately. The simulation results also demonstrate that: (1) When the turning speed is increased, the turning resistance does not change significantly but leads to a more sufficient mixing of the soil; (2) There exists a critical turning angle above which the resistance increase significantly associates with a larger angle; (3) Increasing the burying depth of the tool helps to improve the mixing effect; however, leads to larger resistance as well. [ABSTRACT FROM AUTHOR]

Numerical techniques in soil-tool interaction play a critical role in the applications of optimal design and optimal control of soil-engaging components. However, one of the greatest challenges in the simulation of soil-tool interaction is the complex dynamic behaviors of the soil in the regime of large deformations, and the analysis and evaluation of forces at the soil-tool interface. Recently smoothed particle hydrodynamics (SPH) has shown its advantages in modeling large deformation problems with deformable boundaries and moving interfaces. In this paper, an SPH model of soil-tool interaction based on the elastoplastic constitutive is established. Firstly, the cutting process and soil-tool interaction for both non-cohesive and cohesive soil are simulated based on a shear failure model and a contact algorithm. The simulation results for non-cohesive soil and cohesive soil in different operating conditions are discussed separately, and the results for different operating conditions are compared. In addition, interactions between soil and inclined short flat blades are also simulated to estimate the cutting force during the tillage process. The predicted soil configuration and cutting force are in good agreement with our experiments and with the results in published literature. The cutting forces for non-cohesive soil exhibit similar trends and average values throughout the process. For cohesive soil, the cutting force curve has a wavy trend and the average value in a stable state is greater than for non-cohesive soil. In order to further validate the feasibility and precision of the presented model, different tillage conditions (cutting angles and depths), internal friction angles for non-cohesive soil, different cohesion for cohesive soil, and different friction coefficient of the cutting blade are all discussed. This work has demonstrated that the proposed model is accurate in soil-tool interaction simulations and can also provide an accurate description of the shear fragmentation of cohesive soil. It helps to contribute to a better understanding of the tillage process that is fundamental and essential for the optimal design of the soil-engaging components. • A high-precision SPH model based on soil elastoplastic constitutive of soil-tool interaction is presented. • The soil elastoplastic constitutive model is modified by a fracture model for cohesive soil failure simulations. • The soil-tool interaction model is suitable for non-cohesive soil and cohesive soil. [ABSTRACT FROM AUTHOR]

Investigation of the strength, deformation and constitutive model of rocks under true three-dimensional stress is of much significance to scientifically and accurately predict the integrity of underground gas storage caprock. In general the intermediate principal stress and the minimum principal stress to which the caprock is subjected are not equal, and there is uncertainty in the in-situ stress test. In this study, the siltstone is taken from the caprock of the Hutubi gas storage in Xinjiang, with a buried depth of 3600 m. A series of true triaxial compression tests on siltstones were carried out using a true triaxial testing system for rocks, and the strength and deformation characteristics of siltstones under different intermediate principal stress conditions were studied. The elastoplastic constitutive model of rocks has been established: in the plastic part, the Mogi-Coulomb yield criterion has been modified so as to obtain the triple-mean-normal-stress yield function and triple-mean-normal-stress potential function suitable for rocks under the true three-dimensional stress state. The hardening law has been determined by fitting the relationship between the plastic deviatoric shear strain and the deviatoric stress in the true triaxial compression test. The constitutive model and the test data of siltstones have been verified by fitting. Finally, the influence of true triaxial stress on the permeability and breakthrough pressure of caprock siltstones has been discussed. The result indicates that with the increase of intermediate principal stress within a certain range, the peak strength of siltstones will also increase, and deformation in the direction of the intermediate principal stress will be restrained. Compared with the potential functions in other constitutive models, the triple-mean-normal-stress potential function proposed in this paper can accurately describe the plastic flow direction of siltstones under the true three-dimensional stress state. And the hardening law truly reflects the plastic deformation of siltstone specimens under different stress states during the loading process. The calculation result of the constitutive model is in good agreement with the test result. Under the true three-dimensional stress, the permeability of siltstones shows anisotropy. With the increase of the intermediate principal stress, the minimum value of siltstone permeability decreased by 8%, and the maximum value of breakthrough pressure increased by 4.3%. • The deformation and strength of rocks under the true three-dimensional stress are studied. • The triple-mean-normal-stress potential function proposed can truly describe the plastic flow direction. • A constitutive model emphasis on plastic potential and hardening law of rocks is established and verified. • The anisotropy of rock permeability is confirmed under the true three-dimensional stress. [ABSTRACT FROM AUTHOR]

The constitutive model of structured clays under cyclic loads is helpful to analyze the long-term stability of foundations, such as subgrade under traffic loads and foundation of an offshore gravity platform under wave loads. Responses of structured clays under cyclic loading depend on the applied cyclic stress and can be phenomenally divided into the cyclic stability, cyclic critical state and cyclic degradation. Among these three types, the cyclic stability is directly related to the long-term stability of structured soil foundations. To analyze the cyclic stability of structured soft clay, the constitutive responses under cyclic loads of different amplitudes are firstly discussed according to the shakedown theorem. Secondly, based on the modified Cam-clay model and the plastic hardening rule proposed by Li and Meissner, an elastoplastic two-surface model is herein developed to simulate the long-term responses of saturated structured soft clays under undrained cyclic loading. In the model, a special parameter for describing progressive damage of soil structure is introduced into the interpolation function of plastic modulus, which is related to the accumulated plastic deviatoric strain. The comparisons of theoretical computations with experiment data from some researchers are finally presented to demonstrate the simulation capability of this model. It is shown that the accumulated strain and the pore water pressure of soft clays under long-term undrained cyclic loading have been well simulated. Moreover, the impact of the cyclic stress ratio (CSR) on the cyclic stability is evaluated by using the empirical formula between the model parameters and the CSR. In addition, the method for calibrating the model parameters is also proved to be reasonable and feasible, thus enabling the model parameters to be determined rigorously. • The cyclic stability of soft soils is an important feature for analyzing the long-term stability of structure foundation under cyclic loading condition. This investigation attempts to analyze the cyclic stability of structured soft clays with the help of elastoplastic model. • An elastoplastic two-surface model which can describe the cyclic stability and ratcheting of saturated soft clay under long-term cyclic loading is established. • A special parameter which can describe the damage of soil structure is introduced into the interpolation function of plastic modulus newly introduced by the authors for characterizing the plastic modulus of the loading surface. • The empirical formulae between the model parameters and the cyclic stress ratio (CSR) are established and proved to be reasonable and feasible. [ABSTRACT FROM AUTHOR]

A series of experiments were performed to investigate the hydraulic and mechanical behavior of an unsaturated silt obtained from the Yellow River Delta. To identify the key factors that influence the soil-water characteristics (SWC), an experimental program was designed to study the SWC of the soil at different void ratios and vertical pressures. It was shown that an apparent hysteresis phenomenon occurred on the SWC curves when the soil experienced drying/wetting cycles. It was also shown that the influence of void ratio on the SWC was significant, and the stress state influenced the SWC only through changing the void ratio. Isotropic compression tests were conducted at different constant matric suctions, using a suction-controlled double cell triaxial apparatus. The soil under shearing showed apparent dilatant and softening behavior, in a way similar to medium to dense sand. In addition, the hardening effect of matric suction was significant, and both the stiffness and peak strength of the soil increased with matric suction. Based on the experimental observations, an elastoplastic constitutive model coupling capillary hysteresis and plastic deformation was developed, in which a hysteretic SWC relationship was introduced to characterize the influence of hydraulic history on the skeletal deformation. To better simulate the volumetric change of the soil, a nonassociated flow rule was adopted. The effect of the plastic volumetric strain on water-retention behavior was also taken into consideration. The proposed model was used to simulate the behavior of unsaturated silt under constant-suction, isotropic compression and constant-suction, triaxial shearing conditions, showing the capability of the new model in describing the behavior of unsaturated silt. [ABSTRACT FROM AUTHOR]

A simple numerical simulation method is proposed to investigate the mechanical response of the unsaturated stratum under the water environmental load. The proposed numerical simulation method applies the water environmental load to the unsaturated stratum as the load condition, and adopts the developed non-orthogonal elastoplastic constitutive model for unsaturated soil to describe the mechanical behaviors at the material scale. The mechanical response of unsaturated stratum is obtained by solving the discretized governing equation of the mechanical equilibrium. The proposed numerical simulation method is implemented based on the commercial finite element software ABAQUS. The effectiveness of the proposed method is verified through the element tests on the Botkin silt, the element tests on the Pearl clay, and a model test of the rising water level on a sand column. The numerical simulations of the rising and decreasing groundwater level in the unsaturated stratum are conducted. During the rising groundwater level, the non-collapsible stratum produces rebound deformation, the collapsible stratum below the groundwater level occurs rebound deformation, and the collapsible stratum above the groundwater level mainly produces settlement deformation. During the decreasing groundwater level, both the collapsible stratum and the non-collapsible stratum produce the settlement deformation. [ABSTRACT FROM AUTHOR]

A modified anisotropic elasto-plastic model is presented in this paper based on the frame work of Modified Cam-clay model and Original Sekiguchi-Ohta model by applying a new stress ratio parameter, through which the yield locus and hardening axis in the p-q plane were adjusted to give a more reasonable description of the practical excavation stress path from initial K0 state. Typical excavated soil slope was selected as the illustration example to carry out the finite element numerical analysis by applying four constitutive models (Original Cam-Clay, Modified Cam-Clay, Original Sekiguchi-Ohta and Modified Sekiguchi-Ohta). The calculated displacements of the slope with above different constitutive models were then compared with the measured infield data. It was found the field measured data agree better with the results calculated from modified model, which indicates that the modified anisotropic model is more suitable in the description of the stress path of excavated soils slope after K0 consolidation.