Overturning Stability of a Rigid Retaining Wall for Foundation Pits in Unsaturated Soils

The soils surrounding foundation pits are commonly unsaturated, but routine anti-overturning calculations of retaining walls are conducted assuming saturated soil mechanics. The primary objective of this paper is to present a simple method for the anti-overturning design of a rigid retaining wall for foundation pits in unsaturated soils. The earth pressure of the Rankine theory for unsaturated soils is adopted to derive the resisting and driving moments with respect to the toe of the retaining wall. The closed-form equations of embedment depth are derived with two different distributions of matric suction. The obtained result is easy to use and has wide applicability and excellent extensibility by considering comprehensive effects from many factors. The validity of the proposed simple method is demonstrated by comparing it with a lower bound solution. Engineering application procedures for this simple method are detailed, and parametric studies about a new defined overturning buried coefficient are discussed. It is found in this paper that the anti-overturning design ignoring matric suction is too conservative; the overturning buried coefficient is significantly influenced by matric suction and its distribution, the suction angle, and effective shear strength.