Theoretical Survey to Study the Hydraulic Characteristics of Saturated Sand Soils Using Buckingham Theory

Review of Numerical Modeling Studies and the Influence of Compaction, Moisture, and Particle Size on Slope Stability

Analysis and evaluation of hydraulic conductivity using various field data: an example from Southwest China

Influence of varying suction conditions on the shear strength of a clayey silt soil

Unsaturated soil mechanics is a crucial area of geotechnical engineering that has gained increasing importance in recent years. However, despite its relevance, no standard guidelines have yet been implemented to study unsaturated behaviour in laboratories. This gap limits professionals’ ability to address practical challenges in arid and tropical regions, particularly in problematic soils under shallow foundations, as well as in collapsible and expansive soils. In addition, critical geotechnical structures such as earth dams, slopes, and pavements require expertise in this field. In this context, the main objective of this study was to analyse the influence of varying suction conditions on the shear strength of a problematic clayey silt soil, which exhibits a macrostructure and microstructure with highly compressible characteristics and sensitivity to moisture variations. The research was conducted following ASTM standards for physical and compressibility characterisation. Specific methods included the consolidated drained triaxial compression test with controlled suction (CID-CA-CS) and the unconsolidated undrained (UU) triaxial test for unsaturated mechanical characterisation. The PRISMA model was also applied to define the strength parameters of saturated soil and estimate the linear failure envelope of unsaturated soil. The key findings include an increase in shear strength to 102.8, 128.8, and 157.4 kPa for matric suction values of 81.3, 160.2, and 246.9 kPa, respectively. This research concludes that suction plays a fundamental role in soil strength and stiffness. Additionally, when suction is lost, the soil undergoes significant deformations under loading. Finally, the reconstituted state of the material and unconsolidated undrained conditions are not representative to evaluate its unsaturated soil behaviour.

The influence of suction and density on the resilient modulus of undercompacted soils

The resilient modulus is a key parameter in road and railway subgrade design, reflecting soil stiffness under repeated loading. While subgrades are typically compacted to maximum dry density, many existing infrastructures are supported by soils with densities lower than the maximum due to inadequate compaction or long-term density loss. Understanding the behaviour of these undercompacted and often unsaturated soils is therefore essential for both infrastructure assessment and design. This paper reviews the influence of cyclic stress, suction, density, and drying–wetting cycles on the resilient modulus of four unsaturated soils with high fines content using experimental data from the literature. The analysis indicates that resilient modulus increases with suction but decreases with increasing cyclic stress for these soils. Resilient modulus is also found to decrease significantly with reductions in density at all suction levels. Moreover, drying–wetting cycles were observed to cause soil deterioration, leading to stiffness degradation and a reduction in resilient modulus of the soil examined. A review of several predictive models showed that neglecting the influence of density and drying-wetting cycles results in weaker agreement between model predictions and experimental observations. To address these limitations, a new model is proposed that incorporates the effects of density variations and soil deterioration due to drying–wetting cycles, leading to improved predictions of the resilient modulus for undercompacted soils.

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.

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.