Undrained Sand Behavior in Axisymmetric Tests at High Pressures

Abstract

The results from an experimental study of undrained granular material behavior at high pressures are presented. Axisymmetric specimens of dense Cambria sand were tested in undrained triaxial compression tests between initial effective confining pressures of 6.4 and 68.9 MPa. Undrained triaxial extension tests between initial effective confining pressures of 12.0 and 52.0 MPa were also performed. Uniform strains in extension specimens were enforced by creating a rigid jacket around the specimen, which prevented necking, but allowed unimpeded deformations in the specimen. It consisted of two layers of spaced steel plates, which were bent to fit the contours of the specimen. The layers of plates are separated by greased rubber membranes. The high confining pressures cause large amounts of particle crushing to occur, which in turn cause the development of large positive pore pressures. This caused the effective stress path to move rapidly toward the effective stress failure envelope. The Mohr-Coulomb, effective stress, secant friction angles in both compression and extension appear to be approximately the same. The applicability of critical state soil mechanics at high pressures is explored.