In this paper, the thermodynamics of granular material is developed to get constitutive relations for unified modelling of undrained viscoplastic flow behavior with complex combined effects of state, rate, time, and path. The proposed formulations of energy storages and dissipations lead to the state-dependent hyperelasticity with an elastic instable region and the viscoplasticity with considerations of the granular kinetic flow. Subjected to strict thermodynamic restraints, a generalized law of viscoplastic shear flow is proposed for granular material as the combination of state-based and rate-based viscoplastic flows, which predictively captures the diversity of undrained granular flow pattern with elastic-plastic coupled non-coaxialities among stresses, (total/ viscoplastic/elastic) strains, and their increments. The viscoplastic flow is also linked with the granular temperature that accounts for the granular kinetic fluctuation varying from dilative dense flow to large unlimited flow under shear-induced static liquefaction. This enables predictions of the creep and the stress relaxation as well as the over- and -under shooting of stress under stepwise changes in strain rate. The model is well validated by predicting the flow potential, phase transformation, critical state, and rate/time effects under undrained conventional triaxial shearing and simple shearing for Toyoura sand, which are strongly related to the void ratio, the confining pressure, the shear stress, and the shear mode.

In order to estimate accumulated excess pore pressures in the soil around a cyclically loaded (offshore) foundation structure, cyclic laboratory tests are required. In practice, the cyclic direct simple shear (DSS) test is often used. From numerous undrained tests (or alternatively tests under constant-volume condition) under varying stress conditions, contour diagrams can be derived, which characterize the soil's behavior under arbitrary cyclic loading conditions. Such contour diagrams can then be used as input for finite element models predicting the load-bearing behavior of foundation structures under undrained or partially drained cyclic loading. The paper deals with the general behavior of a poorly graded medium sand in cyclic DSS tests under undrained loading conditions. The main objective of the research was to investigate and parametrize the soil's behavior and to identify possible effects of sample preparation. Numerous tests with varying cyclic stress ratios (CSR) and mean stress ratios (MSR) have been conducted. Also the relative density of the sand was varied. A new set of equations for a relatively easy handable mathematical description of the resulting contour plots was developed and parametrized. In the original tests, the sand was poured into the testing frame and carefully compacted to the desired relative density by tamping. In offshore practice, a preconditioning of a soil sample is usually realised by cyclic preshearing with a certain CSR-value or additionally by preconsolidation under drained conditions. By that, a more realistic initial state of the soil shall be achieved. In order to investigate the effect of such a preconditioning on the resulting contour diagrams, additional tests were conducted in which preshearing and preconsolidation was applied and the results were compared to the test results without any preconditioning. The results clearly show a significant effect of preshearing and an even more pronounced effect of preconsolidation for the considered poorly graded medium sand.

Accurately predicting pile penetration in marine soft clays is crucial for effective construction, load-bearing design, and maintenance of offshore pile foundations. A semi-analytical solution employing the combined expansion-shearing method (CESM) is introduced to model pile penetration in soft clays. This method innovatively simplifies the Pile penetration into undrained cavity expansion and vertical shearing. Using the S-CLAY1S model, which incorporates the anisotropy and structure of natural soft clays, an exact semi-analytical solution was developed to describe soil behavior around the pile under undrained vertical shearing, expanding upon existing undrained cavity expansion solutions. The accuracy and innovation of the CESM were validated through the results of field tests and finite element simulations. Additionally, a comprehensive parametric study highlighted the significant impact of soil's initial structure and stress state on pile penetration response. The study findings strongly align with theoretical calculations, field Measurements, and numerical simulations. Compared to the conventional cavity expansion method, CESM excels in resolving soil stresses at the pile shaft, albeit with a slight limitation in evaluating excess pore water pressure of soils at the pile shaft. The proposed solution considers the fundamental properties of soft clays, including their anisotropy and structural behavior, while incorporating the vertical shearing experienced by the soil during pile installation, thereby providing a simplified yet precise theoretical framework for addressing pile penetration challenges.

In this study, a high-confining pressure and real-time large-displacement shearing-flow setup was developed. The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing permeability and injection-induced seismicity during hot dry rock geothermal extraction. For optimizing injection strategies and improving engineering safety, real-time permeability, deformation, and energy release characteristics of fractured granite samples driven by injected water pressure under different critical sliding conditions were evaluated. The results indicated that: (1) A low injection water pressure induced intermittent small-deformation stick-slip behavior in fractures, and a high injection pressure primarily caused continuous high-speed large-deformation sliding in fractures. The optimal injection water pressure range was defined for enhancing hydraulic shear permeability and preventing large injection-induced earthquakes. (2) Under the same experimental conditions, fracture sliding was deemed as the major factor that enhanced the hydraulic shear-permeability enhancement and the maximum permeability increased by 36.54 and 41.59 times, respectively, in above two slip modes. (3) Based on the real-time transient evolution of water pressure during fracture sliding, the variation coefficients of slip rate, permeability, and water pressure were fitted, and the results were different from those measured under quasi-static conditions. (4) The maximum and minimum shear strength criteria for injection-induced fracture sliding were also determined (m = 0.6665 and m = 0.1645, respectively, m is friction coefficient). Using the 3D (three-dimensional) fracture surface scanning technology, the weakening effect of injection pressure on fracture surface damage characteristics was determined, which provided evidence for the geological markers of fault sliding mode and sliding nature transitions under the fluid influence. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The stimulation of shale reservoirs frequently involves significant shear failure, which is crucial for creating fracture networks and enhancing permeability to boost production. As the depth of extraction increases, the impact of elevated temperatures on the anisotropic shear strength and failure mechanisms of shale becomes pronounced, yet there is a notable lack of relevant research. This study conducts, for the first time, direct shear experiment on shales at four different temperatures and seven bedding angles. By employing acoustic emission (AE) and digital image correlation (DIC) techniques, the evolution of damage and the mechanism of crack propagation under anisotropic direct shearing at varying temperatures is revealed. The results indicate that both shear displacement and strength of shale increase with temperature across different bedding angles. Additionally, shale demonstrates distinct brittle failure characteristics under various conditions during direct shearing tests. The types of anisotropic shear failure observed under the influence of temperature include central shearing fracture, central shearing with secondary fracture, and deflected slip along the bedding. Moreover, the temperature effect enhances shear-induced crack propagation along bedding planes. Shear failure in shale predominantly occurs during higher loading stages, which coincide with a substantial amount of AE signals. Finally, the introduction of the anisotropy index and temperature sensitivity coefficient further elucidates the interaction mechanism between thermal effects and anisotropy. This study offers a novel methodology to explore the anisotropic shear failure behavior of shale under elevated temperatures, and also provides crucial theoretical and experimental insights into shear failure behavior relevant to practical shale reservoir stimulation. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Although time-dependent deformation of geomaterials underpins slope-failure prediction models, the influence of strain rate on shearing strength and deformation behavior of loess remains unclear. The consolidated undrained (CU) and drained (CD) triaxial testing elucidated the impact of strain rate (0.005-0.3 mm/min) on strength envelopes, deformation moduli, pore pressures, and dilatancy characteristics of unsaturated and quasi-saturated loess. Under drained conditions with a controlled matric suction of 50 kPa, increasing strain rates from 0.005 mm/min to 0.011 mm/min induced decreases in failure deviatoric stress (qf), initial deformation modulus (Ei), and cohesion (c), while friction angles remained unaffected. Specimens displayed initial contractive volumetric strains transitioning to dilation across varying confining pressures. Higher rates diminished contractive volumetric strains and drainage volumes, indicating reduced densification and strength in the shear zone. Under undrained conditions, both unsaturated and quasi-saturated (pore pressure coefficient B = 0.75) loess exhibited deteriorating mechanical properties with increasing rates from 0.03 mm/min to 0.3 mm/min. For unsaturated loess, reduced contractive volumetric strains at higher rates manifested relatively looser structures in the pre- peak stress phase. The strength decrement in quasi-saturated loess arose from elevated excess porewater pressures diminishing effective stresses. Negative porewater pressures emerged in quasi-saturated loess at lower confining pressures and strain rates. Compared to previous studies, the qf and Ei exhibited rate sensitivity below threshold values before attaining minima with marginal subsequent influence. The underlying mechanism mirrors the transition from creep to accelerated deformation phase of landslides. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

A thermodynamics-based constitutive model predicting the critical state behavior of sands is developed in this paper. The model includes hyperelastic and plastic constitutive relations derived from thermodynamics. Using the concept of elastic potential, hyperelastic relations are derived to describe the stress- and -density dependency of the elastic stiffness of sands, which naturally lead to the elastic limit with stress-induced anisotropy in effective stress space. The plastic constitutive relations coupled with the nonlinear hyperelasticity are then derived based on the energy dissipations and the second law of thermodynamics. The model is capable of predicting the critical state behavior of sands without concepts of yield surface and plastic potential surface. The model is validated by predicting the undrained shear behavior of Toyoura sand. The modeling results show that different patterns of undrained shear response, such as the pure dilation type, the contraction-dilation type with hardening, the contraction-dilation type with softening, and the pure contraction type, can be well captured by the model, depending on the confining pressure and the void ratio. The distinctions of contraction/dilation and critical state behavior between triaxial compression and extension are also predicted. It is shown that the critical state behavior of sand is the combined results of the pressure/density/path-dependent hyperelasticity and plasticity coupled with each other.

Particle shape is an intrinsic characteristic of soil particles that significantly influences mechanical responses. In this investigation, a meticulously calibrated and validated two-dimensional discrete element method (DEM) model of a biaxial shearing test was employed to simulate the shearing response of forty distinct particle shapes. The systematic evolution of particle roundness (R) and aspect ratio (AR) was achieved by utilizing idealized polygonal-shaped particles, aiming to comprehend their effects on the macro and micromechanical behaviors of granular materials. The results suggest that a reduction in R limits free rotations and enhances interlocking, thereby promoting relatively stable force transmission between particles and leading to a monotonic increase in shear strength. However, this effect diminishes as particles become more elongated. Conversely, a decrease in AR from 1.0 (increased elongation) constrains particle rotations, increases the coordination number, and enhances fabric anisotropy initially resulting in increased overall shear strength, reaching a maximum before exhibiting a decreasing trend, indicative of non-monotonic variation. For high elongations, notable fabric anisotropy impedes clear force transmission between particles thus facilitating interparticle sliding and overall strength diminishes. The extent to which AR impacts depends on the angularity feature of particles. Finally, a nonlinear equation has been proposed to predict the variation in critical state shear strength of granular samples, based on the R and AR values of the constituent particles.

To investigate the freeze-thaw resistance of hydroxypropyl methylcellulose (HPMC)-modified loess, the study analyzed the effects of HPMC dosage and the number of freeze-thaw cycles on the shear strength of modified loess through triaxial shear tests. The results indicated that the peak stress of modified loess exhibited a tendency to increase and then decrease with the increase of the dosage. The optimal dosage of HPMC was 0.5 %. When the confining pressure were 100kPa and 200kPa, the stress-strain relationship curves of modified loess with optimal dosage after freeze-thaw cycles exhibited a weak hardening behavior; at confining pressures of 300kPa and 400kPa, the stress-strain curves exhibited weak softening behavior. As the number of freeze-thaw cycles increased, the peak stress and shear strength indices of the optimal dosage of modified loess exhibited fluctuations. with the lowest values observed after five freeze-thaw cycles. Based on the peak stress, an anti-freezethaw modification effect parameter was proposed, which exhibited a positive correlation with the number of freeze-thaw cycles. The anti-freeze-thaw modification effect parameters for modified loess with optimal dosage were all greater than 1, indicating that the addition of HPMC significantly enhances the freeze-thaw resistance of seasonally frozen soil. HPMC functions both within the soil and at the air-water interface, forming hydrogen bonds, three-dimensional network structures, and flocculated agglomerates, thereby enhancing the strength and freeze-thaw resistance of the soil.

Vibrators are widely used in agriculture, such as for vibrating trees to harvest fruits and nuts, or for vibrating screens to separate different materials (e.g. plants and soil or grain and debris) in the harvesting process. Traditional vibrators are bulky and configured with fixed mechanical transmission, so they cannot be precisely controlled and cannot adapt to different conditions, causing negative effects such as ineffective vibration or damaging tree barks. In this paper, a full-directional and lightweight electric vibrator is designed. The unidirectional vibration force is produced through the utilization of two centrifugal forces that are generated by the eccentric mass rotation of two motors. Firstly, the vibration direction can be adjusted to any direction by adjusting the meeting position of the two centrifugal forces. Secondly, the vibration force can be adjusted by changing the motor speed, as the centrifugal force is proportional to the square of the rotation speed. The vibrator is tested with laboratory bench experiment and with agricultural application for vibrating a tree. The prototype vibrator can produce 680N with the weight of 7.2kg, the force can be further improved by increasing the eccentric mass, increasing the rotation speed or decreasing the rotation arm length. The vibrator can be applied to smart agriculture, such as nut and fruit harvesting, or adaptive vibration screening.