This paper describes a novel servo-controlled true triaxial apparatus that has been developed to test 3-in (7.5-cm) per side, cubical specimens of unsaturated soil under controlled-suction states for a wide range of stress paths that are 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(s) 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 recently implemented by Hoyos (1998), featuring two independent pore-air and pore-water pressure control systems via a PCP-5000-UNSAT pressure panel. Matric suction states in the cubical specimens are induced during testing using axis-translation technique. The paper outlines the importance and development of the new cell, including a brief overview of its main components and the initial validation of its suitability for testing unsaturated soils utilizing the s = u_a testing concept (u_w = 0).
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