Earth Pressure of Partially Saturated Over-Consolidated Collapsible Soils

Abstract

Collapsible soils are known as unsaturated soils that exhibit high strength when dry, while experiencing a drastic volume reduction when inundated. Due to the constant growth in construction and urban development, dealing with these types of soils has become unavoidable. Collapsible soils are exposed to water during deep excavations, rising the groundwater table, irrigation activities, heavy rainfalls, broken sewer pipes, etc., which results in excessive settlement of foundations, landslides, embankments or slope failures. In most of these structures, retaining walls and earth pressures dominate the design. Numerical models were developed to simulate the case of walls retaining over-consolidated, partially saturated collapsible soils. The models used the finite element technique and the commercial software “ABAQUS” to model walls subjected to at-rest or passive earth pressure. The theory of unsaturated soil mechanics was employed to evaluate the soil parameters at a given degree of saturation. It is of interest to report that for a given collapse potential, the coefficient of the at-rest earth pressure increases with the increase of the degree of saturation up to a maximum value for each over-consolidation ratio, beyond which it decreases with the increase of the degree of saturation, while the coefficient of passive earth pressure decrees with the increase of the degree of saturation. Design charts are presented to estimate the coefficients of at-rest and passive earth pressures for a given collapse potential, over-consolidation ratio, and degree of saturation.