Modified Shear Displacement Method for Analysis of Piles in Unsaturated Expansive Soils Considering Influence of Environmental Factors

Abstract

Pile foundations are widely used in regions with expansive soils to transfer the loads from superstructures to a rigid soil stratum, thereby alleviating stability and deformation problems. However, current design procedures for pile foundations are typically based on saturated soil mechanics principles assuming drained conditions, despite the fact expansive soils surrounding the piles are typically in an unsaturated state. Volume changes of expansive soil induced by matric suction changes upon seasonal wetting and drying can significantly influence the pile load-transfer mechanisms. In this paper, using unsaturated soil mechanics as a tool, theoretical models are introduced for estimations of pile shaft friction and pile base resistance considering both the influences of matric suction changes and matric suction variation-induced volume changes of expansive soil around the pile. The commonly used shear displacement method for interpreting the pile mechanical behaviors is modified by including these models to extend their application to piles in unsaturated expansive soils. The proposed modified shear displacement method (MSDM) is interpreted and successfully validated using a pile infiltration test conducted in the laboratory along with another case study from published literature. The results of investigation studies using the proposed MSDM suggest that it can be a valuable tool for practicing engineers to make reasonable predictions of mechanical behaviors of piles in unsaturated expansive soils.