Analysis of Pile–Soil Interaction Based on an Unsaturated Soil Equivalent Rheological Model

Unsaturated soils constitute a substantial portion of the Earth’s surface, underscoring the critical importance of examining the deep foundation behavior within these soils in the field of geotechnical engineering. This study develops a time-dependent model to analyze pile–soil interactions in unsaturated soils, focusing on the temporal evolution of these interactions following pile installation. By employing an equivalent time-dependent model for unsaturated soils, the stress state surrounding the pile is integrated into the model to account for soil creep behavior postpile driving. Creep is translated into variations in void ratio through a geometric equation. Utilizing the surface strength criterion for unsaturated soils, the temporal variation in shear strength is determined. This shear strength is subsequently employed to formulate a time-dependent equation for pile-side resistance, allowing for an analysis of the temporal behavior of side resistance and its influencing factors. The proposed methodology is validated through comparison with experimental data. The results demonstrate that the shaft friction resistance of jacked piles in unsaturated soils follows a distinct temporal pattern postinstallation, characterized by an initial rapid increase, a subsequent gradual deceleration, and eventual stabilization. During this creep period, variations in matric suction and moisture content exert minimal influence on the extent of resistance enhancement, with only an approximately 5% increase observed under all conditions. As the moisture content increases from 11.7% to 13.7%, 15.7%, and ultimately 17.7%, the shaft resistance initially rises by approximately 21% before declining by about 7.9% at corresponding time intervals. This behavior indicates that shaft resistance initially increases with moisture content up to a certain threshold, beyond which it begins to decrease.