This paper presents the results from a preliminary series of conventional triaxial compression (CTC) and triaxial compression (TC) tests conducted on compacted silty sand (SM) under constant-suction states. The experiments were conducted by using a novel, servo-controlled, true triaxial (cubical) apparatus that is suitable to test 3-in (7.5-cm) per side, cubical specimens of unsaturated soil under controlled-suction states and for a wide range of stress paths that are not achievable in a conventional cylindrical apparatus. The equipment is a mixed-boundary type of device, with the specimen seated on top of a high-air-entry ceramic disk and between five flexible (latex) membranes on the remaining sides of the cube. The cell features two independent pore-air (ua) and pore-water (uw) pressure control systems via a PCP-5000-UNSAT pressure panel. Target suction levels are induced and kept constant during testing using the axis-translation technique. The technique is implemented by utilizing the s = uatesting concept (uw= 0), which plays a fundamental role in characterizing unsaturated soil behavior under multiaxial stress paths that are likely to be experienced in the field. Results from suction-controlled tests under axisymmetric conditions (σ2= σ3) were used for calibration and further fine-tuning of the original elasto-plastic, critical state based framework postulated by the Barcelona Model (Alonso et al. 1990). Matric suction was found to exert a noticeable influence on the soil's stress-strain-strength behavior under multiaxial stress states. Numerical predictions of experimental stress-strain response of silty sand under axisymmetric conditions, using the Barcelona Model, were proved to be reasonably accurate.