Three-dimensional active earth pressure for retaining structures in soils subjected to steady unsaturated seepage effects

Abstract

In extant studies, most of the analyses on active earth pressure focused on dry or saturated soils using two-dimensional failure mechanisms. However, in practice, soils are usually unsaturated, and all failures of retained soil masses indicate a somewhat three-dimensional (3D) feature. This work adopts the kinematic limit analysis method to evaluate the active earth pressure with considering the 3D effect and the presence of vertical steady unsaturated seepage. A closed-form framework for describing the profile of suction stress is adopted, and an extended form of the Mohr–Coulomb failure criterion is introduced to represent the unsaturated soil strength. In the context of a 3D horn-like collapse mechanism, the resultant of active earth pressure is evaluated and expressed as a dimensionless coefficient. Several charts are provided for parametric studies. The obtained results indicate that accounting for either the presence of unsaturated seepage or the 3D effect can lead to a more economical result. This study considers a more realistic service behavior of retaining structures and presents a useful solution for the 3D active earth pressure under unsaturated seepage conditions.