The mitigation of seismic soil liquefaction in sand with fine content presents a challenge, demanding efficient strategies. This research explores the efficacy of Microbial-Induced Partial Saturation (MIPS) as a biogeotechnical technique to improve the liquefaction resistance of sandy soils with plastic fines. By leveraging the natural metabolic processes of indigenous microorganisms, this method introduces biogenic gas production within the soil matrix, effectively reducing its degree of saturation. This partial desaturation alters the soil's response to cyclic loading, aiming to mitigate the risk of liquefaction under dynamic loading conditions. Experimental results from a series of undrained strain-controlled cyclic shear tests reveal that even a modest reduction in saturation significantly enhances the soil's stability against seismic-induced liquefaction. The investigation extends to analyzing the effectiveness of the MIPS treatment in sands with low-plasticity clay content, offering insights into the interaction between microbial activity, soil texture, and liquefaction potential. Results show that while plasticity plays a key role in improving the cyclic response of soils, the influence of MIPS treatment remains noteworthy, even in sand with plastic fines. Additionally, a modified predictive formulation is introduced, incorporating a calibrated parameter to account for the influence of fines' plasticity on excess pore pressure generation.

The laboratory experiment is an effective tool for the rapid assessment of the unsaturated soil slopes instability induced by extreme weather events. However, traditional experimental methods for unsaturated soils, including the measurement of the soil-water characteristic curve (SWCC), soil hydraulic conductivity function (SHCF), shear strength envelope, etc., are time-consuming. To overcome this limitation, a rapid testing strategy is proposed. In the experimental design, the water saturation level is selected as the control variable instead of the suction level. In the suction measurement, the suction monitoring method is adopted instead of the suction control method, allowing for simultaneous testing of multiple soil samples. The proposed rapid testing strategy is applied to measure the soil hydro-mechanical properties over a wide suction/saturation range. The results demonstrate that: (1) only 3-4 samples and 2-5 days are in need in the measurement of SWCC; (2) 7 days is enough to determine a complete permeability function; (3) only 3 samples and 3-7 days are in need in the measurement of the shear strength envelope; (4) pore size/water distribution measurement technique is fast and recommended as a beneficial supplement to traditional test methods for unsaturated soils. Our findings suggest that by employing these proposed rapid testing methods, the measurement of pivotal properties for unsaturated soils can be accomplished within one week, thus significantly reducing the temporal and financial costs associated with experiments. The findings provide a reliable experimental approach for the rapid risk assessment of geological disasters induced by extreme climatic events.

Landslides commonly evolve from slow, progressive movements to sudden catastrophic failures, with saturation and displacement rates playing significant roles in this transition. In this paper, we investigate the influence of saturation, displacement rate, and normal stress on the residual shear strength and creep behaviour of shear-zone soils from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Results reveal a critical transition from rate-strengthening to rate-weakening behaviour with increasing displacement rates, significantly influenced by the degree of saturation. This transition governs the observed patterns of slow movement punctuated by periods of accelerated creep, highlighting the potential for exceeding critical displacement rates to trigger catastrophic failure. Furthermore, partially saturated soils exhibited higher residual strength and greater resistance to creep failure compared to nearly and fully saturated soils, underscoring the contribution of matric suction to shear strength.

Shear strength of hydrate-bearing sediment is an essential parameter for assessing landslide potential of hydrate reservoirs under exploration conditions. However, the characteristics and simulation of this shear strength under varying dissociation conditions have not been thoroughly investigated. To this end, a series of triaxial compression tests were first carried out on sediments with varying initial hydrate saturations along dissociation pathways. Combining measured data with microscale analysis, the underlying mechanism for the evolution of shear strength in hydrate-bearing sediment was studied under varying partial dissociation pathways. Moreover, a shear strength model for hydrate-bearing sediment was proposed, taking into account the hydrate saturation and the unhydrated water content. Apart from the parameters derived from the hydrate characteristic curve, only one additional model parameter is required. The proposed model was validated using measured data on hydrate sediments. The results indicate that the proposed model can effectively capture the shear strength behavior of hydrate-bearing sediment under varying dissociation paths. Finally, a sensitivity analysis of the model parameters was conducted to characterize the proposed model. (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 engineering diseases caused by seasonal sulfate saline soil in Hexi region of Gansu Province seriously affect the local infrastructure construction and operation maintenance. To address this issue, this study explored the thermal mass transfer law, pore fluid phase transition, soil deformation and microstructure of unsaturated sulfate saline soil under the open system. Firstly, based on the theories of porous media mechanics and continuum mechanics, combined with the conservation equations of mass, energy and momentum and considering the phase transition of pore fluid, a multi-field coupled mathematical model of hydro-thermal-salt-gas-mechanical for unsaturated sulfate saline soil was established. Secondly, basic unknown variables such as pore water pressure, concentration, temperature, porosity, and displacement were selected to perform numerical simulation analysis on the equation system by Comsol Multiphysics finite element method. Finally, a comparative analysis was conducted between the on-site measured data and the numerical simulation results. The results show that the water and salt phase transitions caused by temperature change could lead to soil salt heave and frost heave, alter the pore structure of the soil, and reduce the compactness of the soil, ultimately being reflected in the changes in soil porosity. The influence of external temperature on soil temperature gradually decreases with increasing depth, and the sensitivity of frozen areas to external temperature is much higher than that of unfrozen areas. This study not only enriches the theoretical results of thermal mass transfer law and deformation of unsaturated sulfate saline soil, but also provides practical guidance for the prevention and control of engineering diseases in local sulfate saline soil.

This study investigates slope stability under rainfall infiltration using numerical modeling in Plaxis 2D, comparing poorly graded sand (6.5% fines) and well-graded sand (11.9% fines) under high-intensity rainfall of 30 mm/h for durations of 8, 12, 18, and 24 h. The results indicate that, as rainfall duration increases, soil saturation rises, leading to reduced suction, lower shear strength, and decreased safety factors (S.F.s). Poorly graded sand shows minimal sensitivity to infiltration, with the S.F. dropping by only 4.3% after 24 h, maintaining values close to the initial 1.126. Conversely, well-graded sand demonstrates significant sensitivity, with its S.F. decreasing by 25.4% after 8 h and 73.7% after 24 h, due to higher water retention capacity and suction. This highlights the significant contrast in stability behavior between the two soil types. The findings emphasize the critical role of soil hydro-mechanical properties in assessing slope stability, especially in regions with intense rainfall. This study establishes a methodology for correlating safety factor variations with rainfall duration and soil type, offering valuable insights for modeling and mitigating landslide risks in rainy climates, considering the hydraulic and mechanical parameters of the soil.

Previous studies provide ample experimental evidence highlighting the effect of temperature on the volume change response of unsaturated soils. However, analytical efforts to capture the temperature dependency of dilatancy under shear stresses are notably scarce. This paper aims to fill this gap by presenting a thermodynamics-based dilatancy model incorporating the influence of the degree of saturation, temperature, soil type, and suction. The model is derived from the first law of thermodynamics, formulated in terms of stored and dissipative energies. Various sources of energy dissipation, including entropy, water flow, friction, as well as energies associated with volume change and rearrangement of soil grains, are considered. The temperature-dependent model is calibrated, and its accuracy is validated using data from 27 triaxial experiments available in the literature. This data set encompasses tests conducted under different temperatures, suctions, stress states, and initial void ratios. The accuracy of the proposed model is compared to three classic models present in the literature that do not account for suction and temperature. The findings demonstrate that the model adeptly captures the complex stress-dilatancy behavior of unsaturated soils with considerably higher accuracy than alternative models. Further, the proposed model's application to simulate the volume change response is demonstrated for two soils under varying saturation levels. The model can readily be incorporated into constitutive modeling of unsaturated soils under thermo-hydro-mechanical conditions.

Sandy hydrate reservoirs are considered an ideal target for the extraction of marine natural gas hydrates (NGH). However, engineering geological risks, including reservoir sand production and seabed subsidence during the extraction process, present a significant challenge. In 2019, China discovered a high-concentration sandy NGH reservoir with favorable commercial development potential in the Qiongdongnan Basin of the South China Sea, establishing the region as a key focus for future exploration and development efforts. A thorough comprehension of macro-meso mechanical properties of this specific sandy NGH reservoir is essential for the safe and efficient extraction of hydrates. In this study, a novel method is proposed to calculate hydrate saturation of hydrate-bearing sandy sediments (HBSS) with hexagonal close-packed state. A series of undrained biaxial compression with flexible boundary show that hydrate cementation enhances the strength of the sample. However, an excessively high hydrate saturation is likely to induce strain softening, whereas an increase in confining pressure helps to mitigate strain softening. Hydrate cementation promotes the formation of abundant force chains. The inhomogeneous displacement, sliding, and relative rotation of the particles are the primary factors contributing to the formation of X-shaped shear bands, which is related to cemented bond breakage. The primary cause of hydrate cementation failure is tensile stress failure. External loading induces force chains to undergo buckling, fracturing, and restructuring, which governs fabric development. The research outcomes offer novel insights into the inhomogeneous deformation and macro-meso mechanical properties of HBSS at the particle-scale.

Slow-moving landslides are typically characterised by pre-existing shear zones composed of thick, clay-rich, and mechanically weak soil layers that exhibit heightened sensitivity to changes in moisture content and hydrological conditions. These zones, often governed by variations in suction and degree of saturation, play a critical role in the stability and long-term behaviour of slow-moving landslides. In this study, we investigate the influence of the degree of saturation on the mechanical properties of shear-zone soils from a reactivated slow-moving landslide in the Three Gorges Reservoir area, China. A series of laboratory experiments, including consolidation, reversal direct shear, and ring-shear tests, were conducted on reconstituted shear-zone soil samples at varying degrees of saturation. The test results indicate that increasing the degree of saturation has a marked impact on the compressibility of the soils, with saturated samples exhibiting greater compressibility and unsaturated samples demonstrating reduced compressibility. Both shear tests indicate that higher saturation leads to a reduction in peak and residual shear strength, likely due to elevated pore water pressures and a decrease in inter-particle bonding forces. These insights emphasise the need to account for varying degrees of saturation when analysing the mechanical behaviour of slow-moving landslides, contributing to an improved understanding of their deformation patterns and failure mechanisms.

In existing studies, most slope stability analyses concentrate on conditions with constant temperature, assuming the slope is intact, and employ the Mohr-Coulomb (M-C) failure criterion for saturated soil to characterize the strength of the backfill. However, the actual working temperature of slopes varies, and natural phenomena such as rainfall and groundwater infiltration commonly result in unsaturated soil conditions, with cracks typically present in cohesive slopes. This study introduces a novel approach for assessing the stability of unsaturated soil stepped slopes under varying temperatures, incorporating the effects of open and vertical cracks. Utilizing the kinematic approach and gravity increase method, we developed a three-dimensional (3D) rotational wedge failure mechanism to simulate slope collapse, enhancing the traditional two-dimensional analyses. We integrated temperature-dependent functions and nonlinear shear strength equations to evaluate the impact of temperature on four typical unsaturated soil types. A particle swarm optimization algorithm was employed to calculate the safety factor, ensuring our method's accuracy by comparing it with existing studies. The results indicate that considering 3D effects yields a higher safety factor, while cracks reduce slope stability. Each unsaturated soil exhibits a distinctive temperature response curve, highlighting the importance of understanding soil types in the design phase.