Constitutive modeling of unsaturated soil behavior using a refined suction-controlled true triaxial cell: Preliminary observations

This paper presents the results from a comprehensive series of hydrostatic compression, conventional triaxial compression, and triaxial compression tests conducted on compacted specimens of unsaturated clayey sand under constant-suction states. The experiments were conducted using a strain-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 cell is a considerably refined version of the stress-controlled systems previously reported by Hoyos et al. (2001, 2005). Target suction levels are induced and kept constant during testing using the axis-translation technique. Results from suction-controlled tests under axisymmetric conditions were used for calibration and further fine-tuning of the elasto-plastic, critical state-based framework postulated by the original Barcelona Model. Numerical predictions of soil response proved to be reasonably accurate, highlighting the potential of the critical state-based framework for use in the analysis of geotechnical boundary-value problems involving unsaturated soil deposits.