This paper describes a servo-controlled true triaxial (cubical) devicethat has been developed to test 3-in (7.5-cm) side, cubical specimens of unsaturatedsoil under controlled-suction states for a wide range of stress paths not achievable in aconventional cylindrical apparatus. The cell is a mixed-boundary type of device, withthe 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, moreelaborate version of the one previously reported by Hoyos et al. (2005), featuring twoindependent 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 andcontrol system via a PCP-5000-UNSAT pressure panel. Suction states, s = (u_a – u_w),are induced in the specimens via the axis-translation technique. The technique isimplemented by utilizing the s = ua testing concept (u_w = 0). The paper outlines thefull development of the new cell, including details of its main components, the stepby-step assembling process and the selection of the appropriate sample compactionprocess and density for testing compacted clayey sand. The operational cell will playa fundamental role in the complete characterization of unsaturated soil behaviorunder multi-axial stress paths that are likely to be experienced in the field.
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