Side Shear Induced in Drilled Shaft by Suction Change

Abstract

This paper describes an experimental study in which a 305 mm diameter instrumented drilled shaft was installed in a moderately expansive clay soil during the dry season and monitored over a period of about 15 months. The purpose of the study was to investigate the effects of seasonal moisture changes in the soil on the unit shear stresses imposed on the sides of the drilled shaft. The soil in the vicinity of the test shaft was instrumented to measure suction and ground surface movement. The relation between total suction, total stress, and shear strength of the soil at the test site was determined through laboratory triaxial compression testing. Daily rainfall and temperatures were also monitored. Over the course of the study, induced side shear stresses of up to 54 kPa were measured in the test shaft. A simple computational model was developed to relate observed suction changes to unit side shear stresses induced by the expansion of the soil through the use of the laboratory total suction-total stress-shear strength relation.