Rockfill, a coarse granular material commonly used in dam construction, exhibits complex mechanical behavior under generalized stress conditions. This paper investigates the mechanical properties of rockfill through a series of stress-path tests conducted on a self-developed, large-scale true triaxial apparatus with cubical specimens of 60 x 30 x 30cm. Three test series are carried out by varying the mean effective stress, the deviator stress and the Lode's angle, respectively. An elastoplastic constitutive model is presented to describe the behavior of rockfill. An improved dilatancy equation is introduced by considering the phase transformation stress ratio instead of the critical stress ratio.

The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deep geological stress for a long period of time, potentially resulting in large-scale deformations or even instability failure of the underground engineering. Accurate characterization of the creep behavior of the surrounding rock is essential for evaluating the long-term stability and safety of high-level radioactive waste (HLW) disposal repositories. Although the laboratory creep tests of brittle undamaged rocks, such as granite, have been extensively performed, the creep characteristics of fractured surrounding rock under the multi-field coupling environment still require attention. In this study, a series of creep experiments was conducted on Beishan granite, which was identified as the optimal candidate surrounding rock for the disposal repository in China. The effects of various factors, including inclination angle of fractures, stress conditions, temperatures, and water content, were investigated. The experimental results show that the axial total strain increases linearly with increasing stress level, while the lateral total strain, axial and lateral creep strain rates increase exponentially. The failure time of saturated specimens fractured at 45 degrees and 60 degrees is approximately 1.05 parts per thousand and 0.84 parts per thousand of that of dry specimens, respectively. The effect of temperature, ranging from room temperature to 120 degrees C, is minimal, compared to the substantial variations in strain and creep rates caused by stress and water content. The creep failure of specimens fractured at 30 degrees is dominated by rock material failure, whereas the creep failure of specimens fractured at 60 degrees is dominated by pre-existing fracture slip. At a 45 degrees fracture angle, a composite failure mechanism is observed that includes both rock material failure and pre-existing fracture slip. (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/).

Mechanical adhesion among lunar regolith particles significantly influences the shear characteristics of lunar regolith. However, experimental limitations on Earth and challenges in capturing particle-scale information obscure the microscopic mechanisms of adhesion and its interaction with other particle properties, such as shape. This study employs the Discrete Element Method to bridge this gap by incorporating mechanical adhesion and simplifying the particle shape effect. Numerical triaxial shear tests were performed on representative volume elements under densities representative of lunar surface. The study introduced a simplified shape parameter, the rolling friction coefficient mu r, r , representing particle 3D sphericity, which ranged from 0.025 to 1.6. Additionally, the particle surface energy density gamma was adjusted from 0 to 1.28 x 10-- 2 J/m2 2 to model the effects of mechanical adhesion. Stress-strain relationships, friction angles, and microscale mechanics parameters were thoroughly analyzed. Simulation results reveal that under low stress, the e c-ln p relationship remains linear, consistent with critical state sand theory. Significant variability in macro properties is influenced by micro-Newton adhesive forces and rolling friction coefficients (0.1-0.8), particularly in particles with notable irregularities, where adhesion profoundly affects mechanical properties, requiring precise calibration. This research advances the understanding of the shear behavior of lunar regolith, providing critical insights for future simulations and experimental designs.

Overconsolidated (OC) clays are commonly encountered in geotechnical engineering and are subjected to threedimensional (3D) stress conditions. This study proposes a unified plastic potential function for triaxial and 3D general stress conditions, by incorporating the overconsolidation parameter and intermediate principal stress parameter. This function can effectively capture the coupling influence of the overconsolidation degree and intermediate principal stress on the dilatancy characteristics of OC clay. Additionally, it possesses a simple form and clear physical significance, making it easily applicable in constitutive models. Then, a simple bounding surface model in triaxial stress conditions is established by adopting the dilatancy relation and the model is extended to general 3D stress conditions by the transformed method based on spatially mobilized plane (SMP) strength criterion. Finally, the performance of the proposed model is validated through various triaxial shearing tests under a wide range of overconsolidation ration (OCR) and the simulation results of the proposed model are compared with those of the SANICLAY model. The comparative analysis indicates that the proposed model effectively describes the complex characteristics of OC clays by simple theory and it demonstrates significant advantages in deformation and pore water pressure simulation due to the advanced dilatancy relation.

Shear strengths of silty soil were determined for shallow destruction of the soil sites frequently occurring in the Central Plains area. Specimens were prepared with five different clay contents (5, 10, 15, 20, and 25%) prior to compaction at dry densities of 1.60, 1.70, and 1.80 g/cm3. Soil specimens were saturated and then the consolidated undrained shear test was conducted with eight confined pressures ranging from 1 to 400 kPa. Results indicate that the shear strength increases significantly as the clay content increases from 5 to 25%, and the cohesion c shows bilinear function with the inflection point at the clay content of 10%. The difference of cohesion in the high and low stress sections decreases gradually to almost the same value until 25% of the clay content, while the internal friction angle phi decreases with the increase in clay content. Within the range of dry density and clay content tested, the shear strength of silty soil in the low stress range obtained is higher than the measured value. Therefore, for the shallow damage of soil site, the shear strength parameters should consider the low stress test conditions. The bilinear growth of cohesion c with clay content can be attributed to the changes from sand-like soil to clay-like soil with the skeleton of soil specimen transitioning from sand particles to clay grid when the clay content exceeds approximately 10% combined with the results of scanning electron microscopy.

Grouting is a widely used approach to reinforce broken surrounding rock mass during the construction of underground tunnels in fault fracture zones, and its reinforcement effectiveness is highly affected by geostress. In this study, a numerical manifold method (NMM) based simulator has been developed to examine the impact of geostress conditions on grouting reinforcement during tunnel excavation. To develop this simulator, a detection technique for identifying slurry migration channels and an improved fluid -solid coupling (F -S) framework, which considers the influence of fracture properties and geostress states, is developed and incorporated into a zero -thickness cohesive element (ZE) based NMM (Co-NMM) for simulating tunnel excavation. Additionally, to simulate coagulation of injected slurry, a bonding repair algorithm is further proposed based on the ZE model. To verify the accuracy of the proposed simulator, a series of simulations about slurry migration in single fractures and fracture networks are numerically reproduced, and the results align well with analytical and laboratory test results. Furthermore, these numerical results show that neglecting the influence of geostress condition can lead to a serious overestimation of slurry migration range and reinforcement effectiveness. After validations, a series of simulations about tunnel grouting reinforcement and tunnel excavation in fault fracture zones with varying fracture densities under different geostress conditions are conducted. Based on these simulations, the influence of geostress conditions and the optimization of grouting schemes are discussed. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting 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/).

Currently, extreme weather events caused by climate change, such as heat waves, drought, frost, and heavy precipitation, have become a threat to agriculture by detrimentally affecting plant productivity and quality. The overuse of synthetic fertilizers is another major concern damaging the soil quality and water and air quality. In this regard, biostimulants could be a promising and potent solution to address these environmental concerns and meet the need for developing sustainable and green modern agriculture. Biostimulants that are primarily composed of natural substances and/or microorganisms can be broadly divided into non-microbial and microbial categories. In this review, the applications of the main types of biostimulants to plant growth and development are discussed, and the possible associated mechanisms of action are described as well. Furthermore, the current status and challenges relating to commercialization and large-scale implementation under changing climate conditions are covered. Overall, this review article could offer insights and knowledge of biostimulants' uses in agriculture for both academia and industrial sectors.