Temperature and Seepage Effects on 3D Active Earth Pressure of Unsaturated Retaining Walls

Temperature and seepage are critical factors influencing the stability of unsaturated retaining walls, as they modulate soil shear strength through alterations in matric suction. This study proposes a three-dimensional analytical framework for evaluating active earth pressure under thermal and seepage conditions. With a kinematic upper-bound approach, temperature-dependent suction evolution and steady-state seepage are incorporated into a horn-shaped failure mechanism. The proposed method is validated against published analytical/numerical solutions, confirming its reliability. A systematic parametric study is conducted to examine how temperature, seepage velocity, wall geometry, and soil pore characteristics affect the active earth pressure behavior. The results reveal distinct behavioral trends depending on soil type: for sand, the active earth pressure increases with rising temperature, indicating reduced stability; conversely, for clay, it decreases with temperature elevation, suggesting enhanced stability. While seepage has minimal impact on sand, it exhibits a clear directional dependence in clays, with infiltration increasing active thrust and evaporation promoting stability through suction recovery. Three-dimensional analysis yields substantially lower earth pressure values compared with conventional two-dimensional approaches, highlighting potential design economies. The proposed method provides engineers with a practical tool for coupled thermal hydraulic mechanical analysis of retaining walls in unsaturated fills, facilitating more realistic and cost-effective designs under varying environmental conditions.