A New Method for Determination of 3D Active Earth Pressure of Unsaturated Backfills

Determinations of active earth pressures are commonly performed two-dimensionally (2D) based on completely saturated and/or dry assumptions, though the soil in cases of geotechnical interest is mostly unsaturated and the earth pressures are usually of conspicuous three-dimensional (3D) features. In this paper, a novel finite prismoid element method (FPEM) for calculating the lateral earth pressures acting against the retaining wall is suggested. The main feature of the FPEM is that the whole backfill is discretized into numerous horizontally distributed prismoid elements that might characterized with different soil properties. For unsaturated backfills, the prismoid elements are characterized with various soil cohesions and unit soil weights. Upper bound solutions to active earth pressures under 2D and 3D conditions with and without suction are both calculated and compared with several other analytical ones, indicating the reliability and applicability of the proposed method. The responses of unsaturated backfills to surcharge loads on the crest are numerically studied and discussed. An illustrative example is reexamined to further demonstrate the practical use of the technique.