This paper presents pore unit assembly-discrete element model (PUA-DEM), a pore-scale hydromechanical framework that resolves interactions between mobile granular particles and multiphase fluids in unsaturated granular media. The framework uniquely integrates DEM with pore-scale hydrodynamic models to capture unsaturated flow dynamics, while leveraging a two-way coupling mechanism to ensure bidirectional fluid-grain feedback through stabilized domain partitioning. Further innovations include a dynamic pore-merging and retriangulation algorithm that enhances computational efficiency for large-scale systems. Validated against experimental data for glass beads and Ottawa sand, PUA-DEM accurately reproduces critical hydromechanical phenomena-including capillary/viscous fingering, wetting-induced granular swelling/collapse, and quasi-static deformation-under diverse saturation and loading regimes. Numerical case studies reveal how capillary forces and wetting fluid saturation collectively govern granular response, from pore-scale meniscus evolution to macroscale flow instabilities. By bridging pore-and particle-scale physics, PUA-DEM advances predictive modeling of partially saturated granular systems, offering transformative insights for geohazard mitigation, sustainable agriculture, pharmaceutical manufacturing, and energy-related engineering applications.

Methane gas hydrate-bearing sediments hold substantial natural gas reserves, and to understand their potential roles in the energy sector as the next generation of energy resources, considerable research is being conducted in industry and academia. Consequently, safe and economically feasible extraction methods are being vigorously researched, as are methods designed to estimate site-specific reserves. In addition, the presence of methane gas hydrates and their dissociation have been known to impact the geotechnical properties of submarine foundation soils and slopes. In this paper, we advance research on gas hydrate-bearing sediments by theoretically studying the effect of the hydromechanical coupling process related to ocean wave hydrodynamics. In this regard, we have studied two geotechnically and theoretically relevant situations related to the oscillatory wave-induced hydromechanical coupling process. Our results show that the presence of initial methane gas pressure leads to excessively high oscillatory pore pressure, which confirms the instability of submarine slopes with methane gas hydrate accumulation originally reported in the geotechnical literature. In addition, our results show that neglecting the presence of initial methane gas pressure in gas hydrate-bearing sediments in the theoretical description of the oscillatory excess pore pressure can lead to improper geotechnical planning. Moreover, the theoretical evolution of oscillatory excess pore water pressure with depth indicates a damping trend in magnitude, leading to a stable value with depth.

This work is devoted to numerical analysis of thermo-hydromechanical problem and cracking process in saturated porous media in the context of deep geological disposal of radioactive waste. The fundamental background of thermo-poro-elastoplasticity theory is first summarized. The emphasis is put on the effect of pore fluid pressure on plastic deformation. A micromechanics-based elastoplastic model is then presented for a class of clayey rocks considered as host rock. Based on linear and nonlinear homogenization techniques, the proposed model is able to systematically account for the influences of porosity and mineral composition on macroscopic elastic properties and plastic yield strength. The initial anisotropy and time-dependent deformation are also taken into account. The induced cracking process is described by using a non-local damage model. A specific hybrid formulation is proposed, able to conveniently capture tensile, shear and mixed cracks. In particular, the influences of pore pressure and confining stress on the shear cracking mechanism are taken into account. The proposed model is applied to investigating thermo-hydromechanical responses and induced damage evolution in laboratory tests at the sample scale. In the last part, an in situ heating experiment is analyzed by using the proposed model. Numerical results are compared with experimental data and field measurements in terms of temperature variation, pore fluid pressure change and induced damaged zone. (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 license (http://creativecommons.org/licenses/by/4.0/).

Experimental and modeling approaches on the soil water retention of low-plasticity undisturbed silty clay were presented in this study to incorporate the combined effects of the pore structure and volume change. Two experimental procedures under the K0 stress state were performed to understand the dependency of hysteretic water retention on both pore structure and volume change effects. The water retention test results show that the hydraulic hysteresis gradually decays when either the suction or vertical compressive stress increases due to a substantial reduction in the macrostructural porosity. Distinct pore structures, including macro- and transitional extra-pore structures with a median size identified through the Mercury Intrusion Porosimetry technique, can induce a noticeable bimodal feature of the SWRC in capillary suction range. The effect of vertical stress, leading to different initial void ratios but a consistent microfabric, can also considerably restrain the irreversible suction-induced volume change and thus influence the water retention as vertical stress increases. The results from K0 compression tests indicate that the variation in the degree of saturation presents an approximate linear negative correlation with the volume change, and the hydromechanical coupling can be, therefore, interpreted through considering the effect of stress-induced volume change on the variation in the degree of saturation. A novel unified formulation of the hydraulic model was developed by incorporating the modified Gallipoli's SWRC model and an unsaturated volume change equation, which can simultaneously describe the combined effects of a heterogeneous pore structure and an elasto-plastic volume change on the variation in the degree of saturation. The proposed model was found to have a good accuracy compared to the test data, testifying to its enhanced predictive capability in modeling the bimodal water retention and the hydromechanical coupling effect.

The combination of the dipping effect and hydromechanical (H-M) coupling effect can easily lead to water inrush disasters in water-rich roadways with different dip angles in coal mines. Therefore, H-M coupling tests of bedded sandstones under identical osmotic pressure and various confining pressures were conducted. Then, the evolution curves of stress-strain, permeability and damage, macro- and mesoscopic failure characteristics were obtained. Subsequently, the mechanical behaviour was characterized, and finally the failure mechanism was revealed. The results showed that: (1) The failure of the sandstone with the bedding angle of 45 degrees or 60 degrees was the structure-dominant type, while that with the bedding angle of 0 degrees, 30 degrees or 90 degrees was the force-dominant type. (2) When the bedding angle was in the range of (0 degrees, 30 degrees) or (45 degrees, 90 degrees), the confining pressure played a dominant role in influencing the peak strength. However, within bE(30 degrees, 45 degrees), the bedding effect played a dominant role in the peak strength. (3) With the increase in bedding angle, the cohesion increased first, then decreased and finally increased, while the internal friction angle was the opposite. (4) When the bedding angle was 0 degrees or 30 degrees, the water wedging effect and the bedding buckling effect would lead to the forking or converging shear failure. When the bedding angle was 45 degrees or 60 degrees, the sliding friction effect would lead to the shear slipping failure. When the bedding angle was 90 degrees, the combination of the bedding buckling effect and shear effect would lead to the mixed tension-shear failure. The above conclusions obtained are helpful for the prevention of water inrush disasters in water-rich roadways with different dips in coal mines. (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/).