13 - True triaxial failure stress and failure plane of two porous sandstones subjected to two distinct loading paths

Abstract

A comprehensive laboratory study was conducted on the mechanics of failure in two compactive, porous, quartz-rich sandstones, subjected to true triaxial compressive stresses (σ1 ≥ σ2 ≥ σ3). True triaxial experiments using the polyaxial testing apparatus were performed in cuboidal specimens of Coconino (17% porosity) and Bentheim sandstone (24%) as both rocks are representative of formations that tend to undergo compactive deformation. Two sets of tests were conducted on each rock. In tests using the common loading path (constant σ2 and σ3), we demonstrated failure stress and failure-plane angle are affected by σ2. Tests using a novel loading path (constant Lode angle Θ) characterized the failure stress and the failure-plane angle dependence on the mean stress and the Lode angle. Comparison of failure-plane angle was made between the bifurcation theory and experimental data, and qualitative agreement was found between them.