Freeze–Thaw Infiltration Governed by Soil Freezing Characteristic Curves and Hydraulic Impedance in Unsaturated Sands

Multiphysical Modelling of Pile Behaviour Under Combined Vertical and Lateral Loads in Thermally Variable Soils

Mechanisms of freeze-thaw-induced structural degradation in black soil driven by ice lens growth using a phase-field model

Seasonal freeze–thaw processes in black soil critically regulate soil structural stability, hydrothermal migration, and aggregate integrity, thereby influencing water retention, root-zone stability, and agricultural productivity and ecological stability. In cold-region agricultural ecosystems, freeze–thaw-induced changes in pore structure and permeability also strongly influence contaminant migration, retention, and the effectiveness of soil remediation measures by altering water flow pathways and mass transport processes. However, the multi-scale coupled mechanisms linking ice lens growth, hydrothermal transport, and structural degradation under varying initial water content and freezing intensity remain poorly understood. To address this, a thermo–hydro–mechanical phase-field coupled model (THM-PF), specifically adapted for black soil, was developed to simulate interactions among temperature variation, moisture migration, stress redistribution, and pore structural evolution. Gradient cooling experiments (−15 °C to −3 °C), combined with microscopic observations, were conducted to validate the model and elucidate coupled freeze–thaw mechanisms and structural degradation processes under controlled conditions. The results indicate that freeze–thaw fragmentation in black soil is primarily controlled by ice lens-induced segregation stress, exhibiting threshold behavior defined by the critical separation void ratio (e sep ). When this threshold is exceeded under strong freezing, the system rapidly destabilizes, with pore pressure reaching 107 kPa and porosity increasing by up to 546.47% relative to the initial state. Initial water content further regulates degradation pathways: at high water content (>32.3%), ice lens growth dominates and causes severe aggregate breakage (up to 99% after 30 cycles), whereas at low water content (<3.4%), degradation is mainly driven by mechanical friction, resulting in limited structural change (porosity increase of 21.62%). In addition, permeability heterogeneity alters heat transfer pathways by 15°–23°, leading to discontinuous ice lens distribution and enhanced spatial heterogeneity. Structural modification (e.g., gravel–sand incorporation) can reduce temperature gradients by up to 27%, thereby suppressing ice lens development. These results collectively reveal a cascade mechanism of “ice lens segregation → hydrothermal heterogeneity → structural degradation” and highlight the potential risks to soil stability, crop productivity, and contaminant transport in high-intensity freeze–thaw regions. Based on this mechanism, targeted mitigation strategies are proposed, including optimal water content control (<28%), permeability regulation through graded fillers, and layered structural design, providing theoretical guidance and technical support for soil conservation, agricultural management, ecological restoration, and contaminant transport management in black soil regions.

Experimental investigation and conceptual modelling of water-limited transpiration as hydraulic boundary condition in geotechnical engineering problems

Water uptake through plant transpiration is a critical hydraulic boundary condition in modelling geostructures under climatic loading. Transpiration occurs in two regimes: energy-limited, controlled by atmospheric evaporative demand; and water-limited, governed by soil hydraulic conductivity around roots. While energy-limited (potential) transpiration is generally modelled using a physically based approach, the water-limited regime is usually modelled macroscopically by way of an empirical transpiration reduction function. This paper first presents an experimental investigation into the influence of soil hydraulic behaviour and potential transpiration rate on water-limited transpiration. Two soil textures were tested – silty sand and clayey-silty sand – planted with Medicago sativa. The use of high-capacity tensiometers enabled the investigation of an unprecedented suction range in clayey soils. Results show that the water-limited branch of the reduction function is non-linear, and its decay is strongly influenced by unsaturated hydraulic conductivity. Furthermore, the suction marking the transition from energy- to water-limited regimes varied with potential transpiration rate and soil hydraulic behaviour. A novel physically based, closed-form reduction function is then formulated to advance water uptake modelling in the water-limited regime. This function is shown to compactly capture the combined effects of soil hydraulic conductivity, root system architecture expressed through root length density and potential transpiration rate on transpiration in the water-limited regime, consistent with observations from both this experimental campaign and the literature data.

NMR-based characterization of soil-water characteristic curves considering volume change during drying-wetting cycles

The Stability of Unsaturated Lateritic Slopes Under Rainfall Conditions Considering Shear Strength Variability

Rainfall-induced slope failures pose significant risks and economic impacts globally. This study investigates the impact of rainfall on the hydromechanical behavior and stability of unsaturated lateritic slopes, commonly found in tropical regions. By employing both experimental and computational analyses, this research goes beyond traditional assumptions about soil behavior, providing an insight into the behavior of clayey and sandy lateritic soils in unsaturated condition. A probabilistic Monte Carlos analysis highlights the critical role of the variability of soil strength parameters on the assessment of slope stability. Detailed experimental design and computational modeling capture the complex interactions between hydraulic and mechanical soil behaviors, contributing substantial empirical data to geotechnical engineering fields. Notably, the shear strength prediction models adapted for unsaturated soils significantly influence slope behavior, demonstrating similar patterns in factor of safety reduction across different hydraulic models during rainwater infiltration. The analysis also confirmed hydraulic parameters with marked differences in porosity and water retention capacities between the soils impacting their susceptibility to saturation and shear strength reduction under similar conditions. This comprehensive approach not only advances our understanding of lateritic soils under changing climatic conditions but also enhances the predictive capabilities for slope stability, guiding effective risk management and engineering practices in tropical regions.

Numerical modelling of suction diffusion in unsaturated expansive soils under climatic fluctuations

The behaviour of expansive clay soils is highly influenced by climatic variations that govern the hydric exchanges between the atmosphere and the ground surface. These fluctuations cause changes in soil suction, leading to significant volumetric variations in expansive soils and resulting in differential settlements of lightweight structures, which can induce structural damage. Despite the critical role of these hydroclimatic processes, few models are able to describe the evolution of soil suction under realistic boundary conditions. In this study, a two-dimensional diffusion model is proposed to simulate the temporal and spatial evolution of suction beneath a structure, considered as impermeable, under the influence of climatic fluctuations and over selected time steps. The model is based on the numerical solution of the diffusion equation in unsaturated porous medium, formulated in terms of suction. The boundary conditions incorporate a surface water balance accounting for infiltration and evaporation, using meteorological data from the Météo-France SIM2 model. Hydraulic soil parameters, such as unsaturated permeability and water retention curve expressing suction as a function of water content, are defined from empirical relationships reported in the literature. The model is applied to a clay soil whose parameters are derived from the Chaingy experimental site (France) using daily climatic data for the year 2025. The simulations highlight a strong seasonal variability of suction concentrated within the upper soil layers, while the presence of an impermeable surface zone representing the structure significantly attenuates suction fluctuations beneath the foundation and induces marked horizontal gradients during dry periods.