A New Hollow Cylinder Torsional Shear Device for Stress/Strain Path Controlled Loading

Abstract

An automated hollow cylinder torsional (HCT) shear device has been commissioned at Carleton University to enable research on stress rotation and partial drainage. The design incorporates elements to arrest undesirable runaway strains and enable the capture of post peak strain softening in different directions, and the ability to closely follow prescribed loading paths. This device is capable of applying both static and cyclic loading under stress and displacement controlled loading modes. This is one of the first HCT devices built specifically to study the partially drained response of soils under three dimensional loading. Test results demonstrating various capabilities of this device, and the level of confidence in the measurements are presented in this paper. The presented results highlight the importance of drainage boundary conditions, and principal stress rotation on liquefaction susceptibility. The partial drainage condition in soils reveals that a small expansive volumetric deformation due to unfavorable drainage boundary conditions can trigger strain softening and flow in soils that may be stable and strain hardening under undrained loading. Tests along different total stress paths under three-dimensional generalized loading show that the uniqueness of undrained effective stress path can be extended to generalized three dimensional loading.