A Discrete-Element-Based Pore-Scale Hydromechanical Approach to Investigate the Hysteresis Effect on the Unsaturated At-Rest Earth Pressure Coefficient

Accurate design of several geotechnical structures, such as retaining walls and piles, necessitates a thorough understanding of the dependence of earth pressure on various soil conditions. Designing resilient earth structures in a rapidly changing climate requires consideration of soil moisture variations caused by droughts or intense rainfall. Therefore, saturation-dependent alterations in the soil's mechanical behavior, such as lateral earth pressure, are crucial to consider. In this study, a pore scale approach, namely, a coupled discrete element-pore network method, was utilized to study the volumetric behavior of unsaturated sandy soils under at-rest conditions. The simulated oedometer tests indicated that the behavior of the soil under study is nonlinear, regardless of variations in the degree of saturation and the hydraulic hysteresis, in which the elastic and elastoplastic regions can be vividly captured. The higher the suction level, the more stretched the elastic region, highlighting the suction-induced effects on the lateral pressure variation with vertical stress; moreover, the increase in suction results in lower values for the at-rest earth pressure coefficient. Finally, the effect of the hysteresis phenomenon and cycles of drying–wetting on the at-rest pressure coefficient was examined. The effect of drying–wetting cycles was assessed in terms of a new quantity, the so-called degree of hysteresis in K₀. The results indicate that the earth pressure coefficient is highly dependent on the hydraulic path as well as the drying–wetting cycles, where a considerable reduction in the degree of hysteresis in K₀ was observed during the second cycle of drying–wetting and this reduction is more prominent in the samples of lower density.