Model for Lateral Swelling Pressure in Unsaturated Expansive Soils

Abstract

Unsaturated expansive soils annually cause major economic losses and structural damages to foundations and earthen structures, primarily due to exhibiting large amounts of swelling and shrinkage when subjected to variations in water content. If an expansive soil is laterally constrained, lateral swelling pressure can exacerbate the unfavorable characteristics of expansive soil by increasing the lateral earth pressure applied to geotechnical structures. This study presents a model to determine lateral swelling pressure considering transient flow in deformable (swelling) unsaturated soils. The transient profiles of water content and suction versus depth during the wetting process are determined considering a coupled hydromechanical behavior. The interplay between the soil deformation, water content, and hydraulic conductivity is accounted for by linking the soil swelling-shrinkage characteristic curve (SSSCC), the soil water retention curve (SWRC), and the hydraulic conductivity function (HCF). An analytical model for quantifying lateral swelling pressure is then developed using a suction stress-based effective stress, the SWRC, and extended Hook’s law for unsaturated soils. The presented model is built upon the conceptual model that lateral swelling pressure is controlled by infiltration-induced changes in suction stress of a laterally-constrained unsaturated soil. The model offers a generalized framework to determine lateral swelling pressure of expansive soils under different degrees of saturation while accounting for the effect of deformation on water content and suction profiles. The model is validated against results attained from three sets of experimental tests available in the literature. Through the three case studies examined, the proposed model exhibited a reasonable accuracy over a wide range of degrees of saturation from 50% to near fully saturated conditions. The findings of this study can contribute toward more accurate evaluations regarding the performance of geotechnical structures in unsaturated expansive soils.