Modeling unsaturated soil behavior under multiaxial stress paths using a refined suction-controlled cubical test cell

This paper introduces a servo-controlled true triaxial (cubical) device that has been developed to test 3-in (7.5-cm) side, cubical specimens of unsaturated soil under controlled-suction states for a wide range of stress paths not achievable in a conventional cylindrical apparatus. The cell is a mixed-boundary type of device, with the specimen seated on top of a high-air-entry disk and between five flexible (latex) membranes on the remaining sides of the cube. The new cell is an upgraded, more elaborate version of the one previously reported by Hoyos et al. (2005), featuring two independent pore-air pressure and pore-water pressure control systems via a PVC-100-UNSAT pressure panel, as well as a fully computer-driven stress application/control system via a PCP-5000-UNSAT pressure panel. Suction states, s = (u_a - u_w), are induced in the specimens via axis-translation technique. The technique is implemented by using the s = u_a testing concept (i.e., u_w = 0). Results from a preliminary series of hydrostatic compression and triaxial compression tests are presented.