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The influence of the inherent fabric anisotropy of sand and its evolution on the footing bearing capacity and failure mechanism has been modelled and analysed with a multiscale approach that couples the finite-element method (FEM) and the discrete-element method (DEM). In this approach, the material constitutive responses are captured by DEM simulations on representative volume elements (RVEs) assigned to the FEM Gauss points. The inherent fabric anisotropy of sand is reflected by the bedding plane angle α of the RVEs composed of elliptic particles, where α measures the average angle between the long axes of the particles and the horizontal direction. The bearing capacity is found to decrease with an increasing α and the reduction can reach as high as 25%. Asymmetric deformation has been observed in the α other than 0° or 90° cases, which is mainly attributable to the different relative principal directions between the stress and the fabric at the two sides of the domain. Further multiscale analyses reveal that the load-bearing structure of the material expressed by the contact-normal-based fabric tensor is more fragile under the footing loading at one side of the domain and in larger α cases, which offers a micromechanical explanation to the observation of the asymmetric deformation and the decreased bearing capacity with increased α.

In practical engineering, natural soil deposits often sustain an initial driving force prior to cyclic shear, owing to earthquakes, traffic and waves; such asymmetrical loading conditions may significantly affect the liquefaction susceptibility and failure mechanism of sand. To understand the typical cyclic liquefaction responses, comprehensive asymmetrical cyclic loading tests were conducted on sand samples subjected to either compressional or extensional static stress. The results indicated that different stress conditions can result in three distinct failure mechanisms: flow liquefaction, cyclic mobility and residual deformation accumulation. According to the experimental observations, an anisotropic sand model was developed within the framework of the anisotropic critical state theory. The model employed a fabric-dependent dilatancy, and accounted for the effects of the fabric evolution and accumulated loading index on the plastic hardening, in order to better reflect the cyclic degradation of the plastic modulus. The predictive capacity of the model was confirmed through undrained monotonic test results for samples with different densities. Comparisons between the model responses and experimental results indicated the excellent capabilities of the developed model in terms of capturing the typical deformation, strength and fabric characteristics of different cyclic failure mechanisms of sand under either symmetrical or asymmetrical loading conditions.

Flow liquefaction, which is characterized by sudden collapse following the unstable behavior of saturated loose sand, may lead to the most catastrophic consequence of all liquefaction-related phenomena. This note presents a systematic experimental investigation into the flow liquefaction potential of sand under various initial and cyclic shear conditions. The cyclic flow liquefaction responses are compared with the monotonic shear results under an identical initial testing condition. It is found that the effective stress path of a monotonic test appears to envelop that of its corresponding cyclic test. The energy-based liquefaction potential evaluation indicates that the accumulative dissipated energy is uniquely correlated not only with the pore pressure and axial strain induced in sand, but also with the degraded stiffness during cyclic loading. Furthermore, the energy capacity for triggering the flow liquefaction appears to be intimately related to the cyclic resistance of sand; this signifies the potential applicability of energy-based liquefaction potential evaluation using strength data available in conventional analysis.

A unified hypoplastic model is formulated by incorporating the anisotropic critical state theory to describe the fabric effect in sand under both monotonic and cyclic loading conditions. An evolving deviatoric fabric tensor that characterizes the internal microstructure of sand is introduced into the hypoplastic model in conjunction with the intergranular strain concept. A scalar-valued fabric anisotropic variable indicating the interplay between the fabric and the loading direction is employed to account for the impact of fabric anisotropy on both the dilatancy and shear strength of sand. The model is demonstrated to be capable of simulating the anisotropic behavior of sand, using a single set of parameters under both monotonic and cyclic loading conditions, as evidenced by the satisfactory match with experimental results from various sources. In particular, by considering the influence of fabric evolution on the dilatancy of sand, the model adequately accounts for the fabric change effect and accurately captures the deviatoric strain accumulation, cyclic mobility, and the flow liquefaction phenomenon under cyclic loading condition.

In this study, we examined the thermal effects throughout the process of the placement of span-scale girder segments on a 6×110-m continuous steel box girder in the Hong Kong-Zhuhai-Macao Bridge. Firstly, when a span-scale girder segment is temporarily stored in the open air, temperature gradients will significantly increase the maximum reaction force on temporary supports and cause local buckling at the bottom of the girder segment. Secondly, due to the temperature difference of the girder segments before and after girth-welding, some residual thermal deflections will appear on the girder segments because the boundary conditions of the structure are changed by the girth-welding. Thirdly, the thermal expansion and thermal bending of girder segments will cause movement and rotation of bearings, which must be considered in setting bearings. We propose control measures for these problems based on finite element method simulation with field-measured temperatures. The local buckling during open-air storage can be avoided by reasonably determining the appropriate positions of temporary supports using analysis of overall and local stresses. The residual thermal deflections can be overcome by performing girth-welding during a period when the vertical temperature difference of the girder is within 1 °C, such as after 22:00. Some formulas are proposed to determine the pre-set distances for bearings, in which the movement and rotation of the bearings due to dead loads and thermal loads are considered. Finally, the feasibility of these control measures in the placement of span-scale girder segments on a real continuous girder was verified: no local buckling was observed during open-air storage; the residual thermal deflections after girth-welding were controlled within 5 mm and the residual pre-set distances of bearings when the whole continuous girder reached its design state were controlled within 20 mm.

This paper investigates the limiting force profile (LFP) for laterally loaded piles embedded in undrained clay. Based on the three- and two-dimensional finite-element limit analysis (FELA)...

Diffuse instability is a typical failure mode of sand that occurs before the perfect plastic flow condition is attained. Whereas extensive laboratory experiments have demonstrated the macro-scale responses associated with such a failure mode, its underlying microscopic mechanism remains unclear. Therefore, no effective predictions can be made incorporating sophisticated constitutive models of sand, particularly when various drainage conditions are considered. In the present study, diffuse instability is first investigated using the discrete element method (DEM). Herein, partially drained and fully drained conditions are imposed to investigate the instability failure in proportional strain loading and constant shear drained tests, respectively. Then, both macro- and micro-scale second-order work criteria are applied to identify the occurrence of instability. Furthermore, the main features associated with the onset of diffuse instability are presented. The diffuse instability behavior of sand is observed to be closely related to its fabric evolution. Eventually, independent criteria for diffuse instability under various drainage conditions are determined considering the DEM results. In addition, a newly developed anisotropic constitutive model with a fabric evolution law is applied to simulate the mechanical behavior of sand and the instability that ensues. The model exhibits satisfactory agreement with the DEM simulation results. Overall, this study is aimed at elucidating why diffuse instability occurs prior to the plastic limit and how to predict it under various drainage conditions.

It has long been recognized that traditional exact methods may encounter numerical instability when analyzing the free vibration of a continuous partial-interaction composite beam, a type of composite beam which considers the interfacial slip. In contrast to the Euler–Bernoulli beam theory, the form of the general solution for the free-vibration governing equations of partial-interaction composite beams based on Timoshenko beam theory will change dramatically when the frequency is sufficiently high, indicating that shear deformation cannot be ignored at high-order frequencies. To tackle this difficulty, this paper presents a numerically stable and theoretically exact method to analyze the dynamic responses of continuous composite beams with partial-interaction. The new method can effectively overcome the problem of numerical instability encountered by traditional theoretical solutions such as the dynamic stiffness matrix method and transfer matrix method, particularly for high-order vibrations or long-span continuous beams. Some numerical examples are provided to demonstrate the performance of the proposed method.

Behaviour of granular soils subjected to internal erosion involves complex coupling between solid–fluid interaction, skeleton deformation and microstructural evolutions. This paper presents a micro–macro investigation on suffusion in idealized gap-graded and well-graded soils using the coupled computational fluid dynamics and discrete element method. The interaction between soil particles and seepage flow is modelled via momentum exchange between two phases. The progressive loss of fine particles subjected to upward seepage flow at various hydraulic gradients is investigated. The fines content, volumetric contraction and void ratio are monitored to identify the changes of macroscopic states of the soil skeleton. In addition, the microstructural evolution is tracked via particle-scale descriptors such as coordination numbers and force chain statistics. Several clogging–unclogging events which are responsible for the sudden changes of fines content and skeleton response are observed during suffusion. A parametric study indicates that the initial fines content and the hydraulic gradient significantly affect the kinetics of suffusion. Microstructural analyses reveal that the removal of fines is accompanied by the reduction in weak contact pairs and particles with low connectivity.

The reinforcement of shield tunnels with secondary linings is a widely used method to enhance the overall rigidity of tunnels; therefore, ensuring tunnel safety during construction and ope...

Optimal whole life design for railways, highways, runways, and metro lines requires an accurate assessment of how their underlying geomaterials respond to large numbers of wheel-loading cycles. This paper presents an experimental study on a natural UK stiff clay with a cyclic triaxial (CT) and hollow cylinder apparatus (CHCA) that imposed K0 and wheel-loading stress conditions. The focus is on Gault clay, a high overconsolidation ratio (OCR) marine clay deposited in the Cretaceous, whose mechanical behavior is significantly anisotropic and in situ K0 values exceed unity. The clay outcrops under sections of most major highways radiating out of London, as well as the HS1 and new HS2 high-speed railways. The experimental investigation explored how the principal stress rotation implicit in wheel loading increases the magnitudes and changes the sign of vertical strain accumulation, as well as accelerating resilient modulus degradation and accentuating stress–strain hysteresis, all of which affect pavement or rail-track serviceability. The clay’s deformation and pore pressure responses are categorized into stable, metastable, and unstable patterns. Comparisons with related studies on low OCR, low K0 soft clay from Wenzhou in southeastern China, confirm the Gault clay’s generally stiffer prefailure behavior and different cyclic response. The stiff clay’s greater brittleness is also emphasized; particle reorientation occurs readily along distinct shear bands, leading to dramatic shear strength reductions that have a major impact on slope and foundation stability and call for appropriate caution in practical design.

This study examines the influence of particle shape irregularity and elongation on the shear behaviors of granular materials using the 3D discrete element method (DEM). The particles are generated by combining a Fourier shape descriptor-based method with the random field theory and reconstructed in DEM using the overlapping sphere algorithm. A series of drained and undrained triaxial and true triaxial tests are performed to shear the samples with different particle irregularity and elongation to the critical state. The stress and the strain responses, the evolution of the fabric anisotropy and the coordination number are examined and analyzed within the framework of the anisotropic critical state theory. It is found that the consideration of complex shaped particles in DEM produces more realistic sand behaviors, and the shear strength and the dilation of the granular material increase with increasing irregularity and elongation. While elongation in the range of the study has insignificant influence on the location of the critical state line (CSL) on the void ratio-mean effective stress plane, irregularity is found to positively affect both the absolute slope and the intercept of the CSL. The unique fabric anisotropy norm at the critical state is also sensitive to the particle shape and is greater with larger irregularity and elongation.

Multidirectional shearing of granular soils involves shearing more than one shear stress component, and thus may result in more-complex soil responses than unidirectional shearing. This stu...

An optimized finite element method (FEM) based on layer structure method has been put forward, which combined the nonlinear behavior of both the structure and the soil surrounding. The lining is simulated with solid element and meshed finely, while the longitudinal joint between segments is modeled by 6-node line interface element. Nonlinear mechanical behaviors of soil, concrete, reinforcement and interfaces are considered with advanced material models. A parameter study is conducted to reveal the influence of several concerning parameters such as the rotation angle of the ring, the width of surface loading, the offset of surface loading and the depth of the tunnel. To better illustrate the result, several indexes including maximum crack width, crack index and crack ratio is introduced to evaluate and forecast crack behavior. The results show that the crack-resistant ability of the tunnel is slightly enhanced as the rotation angle of the ring increases. A more unfavorable influence can be brought to linings by the shift of the surface loading when its offsetting is smaller than 30 m in the case. However, the influence on segment cracking caused by the change of the tunnel depth is complicated when stress redistribution after tunnel excavation is considered, and there is an unfavorable buried depth when the crack ratio reaches maximum. Finally, a simple fitting equation, which is based on the previously mentioned numerical simulation, is provided to establish the relationship between the horizontal ovalisation and the crack ratio.

The lateral bearing performance of a defective pile-supported wharf located on a slope was investigated through centrifuge modeling, and a numerical model was employed to back-analyze the ...

Displacement piles are driven to support a wide range of structures. Predicting their axial limiting capacities and load-displacement behavior is critical to many such engineering applicati...

As a typical form of internal erosion, suffusion refers to the detachment and migration of fine particles through voids among coarse particles driven by seepage flow. This paper studies the...

A numerical investigation on the behavior of granular materials subjected to the rotation of principal stresses using the discrete element method is presented. A numerical procedure is developed to implement the two-dimensional arbitrary stress or strain paths imposed on polygonal specimens. Significant volumetric strain can be obtained and granular assembly appears to develop an anisotropic internal structure characterized by the contact-normal-based fabric tensor in due course, with its direction being rotated with the rotation of the principal stress. The observations indicate a significant degree of non-coaxiality between the principal-stress direction and the principal-strain increment direction. An ultimate state can be reached after sufficiently large numbers of cycling, resulting in a constant fabric norm and a circular strain trajectory in the deviatoric space. The boundary work, dissipation, and strain energy, are also registered during the entire loading process and its correlation between non-coaxial deformations is analyzed from micro-scale perspective. Before the ultimate state is reached, the applied work is partially dissipated by frictional sliding, and the remainder is stored as the strain energy within the specimen. When the ultimate state is reached, however, no change in the strain energy is obtained, and the plastic work is entirely dissipated, as the elastic portion of the free energy increment only depends on the elastic strain.

A J2-deformation type model coupled with dilatancy is proposed, aiming to eliminate two major deficiencies of Duncan–Chang model in modeling shear responses, i.e. no softening response and no volumetric response. Only four model constants are traditional parameters and can easily be determined in the basic model. The basic model can be extended by incorporating a more appropriate dilatancy expression and modifying the shear response curve to simulate a more realistic behavior of soils. The simulative capacity of the model is demonstrated by the comparisons between the model responses and the test data of both sand and clay.

With the rapid development of the real estate market, real estate evaluation is becoming more and more important and active. The real estate is now evaluated according to the expertise and experience of the appraiser. The evaluation results are often influenced by the subjective randomness of the evaluation personnel and the complicated and changeable environmental factors. It is not only a professional technology, but also a complicated art. Therefore, how to improve the scientific, accuracy and efficiency of real estate evaluation has become an important issue that needs to be studied and solved in the real estate evaluation industry. This paper takes mass real estate evaluation system as the research object, adopts the BP neural network to research the design principles of the evaluation system and the design method of the model, and designs and develops the mass intelligent evaluation system to improve the intelligence, scientific, accuracy and credibility of the evaluation system.

In this paper we propose a degradation model to describe the damage-dependent behavior of saturated soft clay under cyclic loading, which is then applied to the analysis of a caisson breakwater. The degree of damage and remolding of soft clay is quantified by a damage parameter related to the accumulated plastic deviatoric strain. Through the correlation between the maximum pore pressure and the undrained strength of soft clay, we obtain a damage-dependent degradation model that employs the post-cyclic undrained strength degradation coefficient in terms of the cyclic stress ratio and the number of cycles. Based on the Tresca yield criterion, the degradation model of undrained strength of soft clay is numerically implemented in the user interface USDFLD of ABAQUS. The performance of this model is verified by a comparison between numerical results (finite element method) and experimental data (cyclic triaxial test). The model is applied to the numerical simulation of a caisson breakwater resting on a partially sand-filled soft clay seabed under cyclic wave loading. The cyclic stress distribution, pore pressure development, and strength degradation of the seabed soil are presented to illustrate the applicability and efficiency of the model in the analysis of the interaction between offshore structures and soft ground.

Using an assumed vertical retaining wall with a drainage system along the soil–structure interface, this paper analyses the effect of anisotropic seepage flow on the development of passive earth pressure. Extremely unfavourable seepage flow inside the backfill, perhaps due to heavy rainfall, will dramatically increase active earth pressure while reducing passive earth pressure, thus increasing the probability of instability of the retaining structure. A trial and error analysis based on limit equilibrium is applied to identify the optimum failure surface. The flow field is computed using Fourier series expansion, and the effective reaction force along the curved failure surface is obtained by solving a modified Kötter equation considering the effect of seepage flow. This approach correlates well with other existing results. For small values of both the internal friction angle and interface friction angle, the failure surface can be appropriately simplified with a planar approximation. A parametric study indicates that the degree of anisotropic seepage flow affects the resulting passive earth pressure. In addition, incremental increases in the effective friction angle and interface friction angle both lead to an increase in passive earth pressure.

The study presents a lightweight code that implements 2D node-based smoothed particle finite element method (NSPFEM) to fulfill the requirement of modeling large deformation in a variety of research fields and engineering applications. NSPFEM discretizes the problem domain with a set of Lagrangian nodes and employs Delaunay triangulation to build/re-build mesh on the nodes at each time step. It is therefore able to tackle large deformation without suffering from mesh entanglement. The method also adopts the nodal integration technique to avoid interpolation of material variables after remeshing which can eliminate interpolation-induced errors. The code has been built using hybrid C++ and Python programming, and is thus efficient and versatile to couple with other well-developed codes, such as MFront for the incorporation of various constitutive models and YADE , a discrete element method code, for multiscale simulations. The implementation of NSPFEM has first been validated using two examples, i.e., axial vibration of an elastic cantilever beam and a rolling cylinder down incline. Next, the capability and flexibility of the code has been demonstrated by three examples, namely retrogressive slope failure, pullout of a strip plate anchor, and multiscale modeling of trapdoor.

Multidirectional shearing tests on soils in the laboratory suffer from drawbacks such as non-uniformity of stress and unknown horizontal stress of the specimen. As a promising numerical technique, the discrete element method (DEM) enables investigation of the responses of virtual granular samples under general loading conditions and provides ideal numerical results to overcome the aforementioned limitations. In this study, three different drained cyclic tests, including conventional rotational shear, bidirectional circular rotational shear, and bidirectional elliptical rotational shear, were conducted on both isotropic and transversely isotropic samples under various stress ratios and density conditions. In all these tests, the magnitudes of the three principal stresses were kept constant during the entire loading process. Principal stress rotation occurred in one deviatoric stress plane in a conventional rotational shearing test but spatially (not necessarily in one plane) in the other two bidirectional shearing tests. The normalized deviatoric strain increment was decomposed into (1) coaxial and proportional, (2) coaxial and orthogonal, and (3) totally non-coaxial parts in reference to the deviatoric stress tensor. Their evolutions are presented and discussed in detail herein. The internal structure quantified by the contact-normal-based fabric tensor was tracked, and its correlation with the imposed stress path is illustrated.

Vehicle traffic loading appears to contribute significantly to long-term settlement beneath highways, airport runways, and metro lines in China. Wheel loading imposes cycles in both the magnitude and direction of the principal stresses acting on the soils beneath pavement or rail-track structures. Conventional cyclic triaxial (CT) testing, which is not capable of imposing such stress paths, may underestimate how heavy traffic loading affects any underlying soft clay layers. A hollow cylinder apparatus (HCA) can simulate such traffic loading stress paths more accurately, including rotation of the principal stress directions. This paper presents a systematic experimental study of cyclic HCA (CHCA) tests on K0-consolidated saturated soft clay involving cyclic variations in both vertical and torsional shear stresses, along with a parallel programme of CT tests, considering the undrained response of saturated samples of intact soft clay. It is shown that when applied above certain critical cyclic stress ratios, principal stress rotation accelerates excess pore-water pressure and permanent strain development. Corresponding changes are also seen in the resilient modulus and damping ratio trends. The discrepancies between the behaviour of CHCA and equivalent CT tests grow as the cyclic stress ratios increase.

Soils are inherently anisotropic, which may significantly influence their mechanical behavior and the performance of related geostructures. In this study, the response of strip footing on anisotropic sand was investigated using a J2-type deformation model coupled with state-dependent dilatancy and fabric evolution. The capability of the model was validated by simulating several element tests and a centrifuge test of strip footing. Footing tests with varying fabric orientations and relative densities were numerically simulated, revealing the influence of fabric anisotropy on the bearing capacity and its mobilization mechanism. Additionally, the effect of fabric on the failure mode of strip footing, including the pattern of the shear band, displacement field within the sand mass, and progressive failure characteristics, was also investigated. The simulation results obtained using an isotropic model indicate that neglecting the fabric anisotropy may cause severe overestimation of the bearing capacity of the strip footing.

Recognizing the limitation of the existing yield surfaces for clays, a novel type of the yield surface is derived. The shape parameters allow for the distortion of the yield surface from an ellipse to a teardrop shape such that it provides more flexibility for better modeling the shear response for over-consolidated clays. A new bounding surface model has been proposed within a critical state framework, and can predict the realistic behavior of over-consolidated clays under both undrained and drained conditions. The capacity of the model is demonstrated by five different reconstituted clays with representative testing results in the literature.

The K 0 -consolidated soil elements beneath structures like quay walls, bridge abutments, cut and cover tunnels and similar structures may be subjected to static shear involving the rotation of the principal stress prior to cyclic loading, which results in the presence of initial shear stress. A hollow cylindrical apparatus was employed and a series of drained cyclic tests was conducted to examine the effects of the initial shear stress induced by drained static shear prior to the application of cyclic loading. Both the initial vertical stress and the initial torsional shear stress were considered in the drained cyclic deformation behavior. The experimental observations indicate that the initial vertical stress accelerates the accumulation of vertical permanent strain during the first 100 cycles only when the initial vertical stress exceeds the value corresponding to the K 0 -consolidated stress state. The average growth rate of strain increases due to the presence of the initial torsional shear stress. A Critical Static Shear Line (CSSL), initiating from the K 0 -consolidated stress state in the ( σ z − σ θ ) − 2 σ zθ plane, divides the volume change responses into contraction and dilation in subsequent cyclic loading. To account for the combined effects of the initial vertical stress and the initial torsional shear stress on the deformation behavior, a modified model is proposed to predict the vertical permanent strain.

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb’s earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb’s formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions, showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.

Approximately 25% of China's 120 000 km of expressway, as well as many new metro lines and airports, rest on soft clay deposits. However, service settlements are proving larger than expected, especially in southeast China. This note describes laboratory experiments on K0-consolidated intact samples of soft clay taken near Wenzhou, south-east China, that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends. Cyclic triaxial (CT) tests are reported together with cyclic hollow cylinder (CHCA) experiments that imposed cardioid-shaped 2τzθ − (Δσz − Δσθ) stress paths. Cyclic principal stress axis rotation is shown to have an important influence on vertical straining. Once a certain threshold has been exceeded, the resilient and permanent strains developed in the CHCA tests become progressively larger than their counterparts in CT tests conducted at the same vertical cyclic stress ratio, with trends that diverge progressively as vertical cyclic stress ratio increases. Critical cyclic stress ratios can be defined that divide the response into (a) stable, (b) metastable and (c) unstable cyclic ranges. The novel experimental approach and high-quality data reported should aid practitioners and modellers in developing new analyses to address this economically significant geotechnical problem.

In ocean engineering, storm-wave loading imposes irregular cycles in the magnitudes acting on the coastal or seabed cohesionless soils, giving rise to more complex consequences on the their liquefa...

The structural temperatures and thermal effects on the cable forces of a long-span cable-stayed bridge with prestressed concrete girders were monitored. The temperatures were distributed as...

This study examines the influence of particle elongation on the direct shear behaviour of granular materials using the discrete element method. A series of numerical direct shear test simulations were performed, and both the macroscopic and microscopic behaviour of elongated assemblies at the critical state were examined. The macroscopic response of elongated particles exhibits an initial hardening followed by post-peak strain softening, prior to reaching the critical state. The peak state friction angles initially increase and stay stable as the dimensionless elongation parameter ($$\eta$$) increases, whereas the critical state friction angles increase with the increase of $$\eta$$. Independent of the applied normal stresses, all samples reach a critical state at a unique normalized stress ratio (i.e., $$\tau /\sigma = 0.51$$) after ~ 25% shear strain. The stress-fabric relationship is mainly governed by the strong force subnetwork which is more affected by the change of η than the weak force subnetwork. Particle elongation generates a downward shifting of critical state lines (CSLs) in $$e - p^{{\prime }}$$ space. Furthermore, the correlations between CSL parameters and $$\eta$$ are well-fitted by a second-order polynomial function. These findings highlight the significance of particle elongation on direct shear behaviour of granular materials.

A non-equilibrium statistical thermodynamics-based framework for describing elasto-viscoplastic deformations in amorphous materials termed shear-transformation-zone (STZ) theory has been implemented in the material point method (MPM) and applied to the modeling of large-deformation geomechanical problems. Plane strain biaxial shear tests with different loading rates were first performed using the model to emphasize its rate-dependency and to compare its performance with that of a μ(I) rheological model. The model was then utilized to simulate three classical large-deformation geomechanical problems, namely, the granular column collapse, the footing settling on a soft ground, and the soil-pipe interaction. It has been shown from this study that the STZ theory is promising in modeling rate-dependent viscoplastic behaviors of geomaterials, as well as solid–fluid phase transition and strain localization.