Passive earth pressure analysis considering hydraulic and mechanical hysteresis for unsaturated soil

This paper addresses the mechanical characteristics of a passive earth pressure problem taking into account water retention curve (SWRC) hysteresis. Both hydraulic (drying and wetting cycles) and mechanical hysteresis were considered. Parametric studies were carried out at various air entry values (AEV = 5-30 kPa), different wall frictions (delta = 0, 0.33 phi, 0.5 phi, 0.67 phi and delta = phi), and unsaturated conditions (covering the zone from the fully saturated to the transition suction, 0 - similar to 40 kPa) using an upper bound theorem. The numerical results were compared with a passive earth pressure equation based on the limit equilibrium method. The results indicated significant influences of SWRC hysteresis and wall frictions on the passive thrust (P-p) for the modeled suction profiles. An increase of 1.31-fold in P-p was obtained when the AEV changed from 10 to 20 kPa at the water table (H-w) = -2 m. Additionally, the combined effects of AEV and delta were found to be significant. An increase of 4.14-fold in P-p at H-w = -3 m was obtained when comparing the case of AEV = 30 kPa and delta = phi with AEV = 5 kPa and delta = 0. Based on the parametric studies, a series of design charts of the exerted passive thrust were proposed.