Deformation and Shear Strength Behaviors of Overconsolidated Clay from Stress-Path Testing for a Deep Open Cut Excavation

Abstract

A stress-path testing program was proposed and performed to investigate shear strength and deformation behaviors due to an open cut excavation in overconsolidated clay. Stress changes due to the staged excavation for different locations of the slope were estimated and applied on undisturbed specimens using a triaxial testing system. Axial load, chamber pressure, and back pressure were actively controlled to implement the various stress paths. Vertical and horizontal deformations were monitored during the stress paths, and then an undrained compression or extension shearing stage followed. Test results for three cases from the testing program: the crest and the toe of the slope, and the base of the excavation are presented. The clay deposit was found to be non-expansive, based on the deformation behaviors. Effective stresses appeared to govern the vertical and horizontal strains. Failure envelopes for compression and extension were established from the stress path testing. The mobilized undrained shear strength from the stress path approach is substantially lower than one from the conventional method.