Lateral earth pressure on a wall in expansive soils
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This paper presents the prediction of lateral earth pressure on a vertical retaining wall due to suction change in expansive soils. A proposed earth pressure model includes initial and final suction envelopes, suction-volumetric water content relations, suction compression indices, and the effect of overburden pressures. The model uses the Mohr's strength envelope, effective stress and shear strength of unsaturated soil, and the passive stress state in a soil. Vertical earth pressure distribution is composed of an upper movement active zone caused by soil swelling and an anchor zone below zero swell depth. Three typical horizontal stress sub-zones are characterized based on stress states: (1) an upper passive failure state zone at which the maximum lateral earth pressures occur at a shallow depth, (2) passive stress state zone due to large suction change and (3) at rest condition zone. The lateral earth pressure increase with depth near the ground surface is limited by the maximum soil strength that can be supported by the overburden pressure. At greater depths, the lateral swelling pressure caused by small suction change is less than the classical at rest earth pressure. A case study matching field observations demonstrates that the earth pressure model calculates large lateral earth pressures and passive failures caused by rainfall and evapo-transpiration in the upper soil layer and seasonal change of water table elevation in the lower soil layer, respectively. The prediction of vertical swelling movements and lateral earth pressures are in satisfactory agreement with both the in-situ measurements of the natural earth pressure and measurements from large scale model tests. 2010 Taylor & Francis Group, London.
