Active Earth Pressure from Unsaturated Soils with Different Water Levels

Abstract

The problem of active earth pressure has historically been investigated assuming dry or saturated backfills, ignoring the fact that soils are usually unsaturated in nature. This note proposes a kinematic framework for the estimation of active earth pressure induced by unsaturated backfills with different water levels. Several formulas consisting of linear and nonlinear forms are used to represent the apparent cohesion due to matric suction. The seepage effect is included in this analysis with the water level to be located at any depth below the crest of the retained soil masses. The impact of cracks is also considered as part of the failure mechanism. An explicit function of the resultant active earth pressure is derived using the principle of work rate balance. The results show that the magnitude of unsaturated active earth pressure is influenced by the soil properties and wall geometry as well as by the models used to estimate the apparent cohesion due to matric suction.