Experimental and Numerical Evaluation on the Response of Unsaturated Compacted Soils under Triaxial Conditions

This paper presents the findings from a series of constant suction triaxial tests conducted on compacted sand and silty sand under unsaturated conditions. These tests were carried out using a fully automated double-walled triaxial cell employing the axis translation technique. The net mean stresses applied ranged from 50 to 250 kPa, while matric suctions were maintained at 0, 100, and 200 kPa. The primary objective of this study was to elucidate the mechanical behavior of the two compacted soils under triaxial conditions, particularly focusing on the influence of suction on variables such as peak stress, apparent cohesion, critical state stress, postpeak softening, and strain-induced dilatancy. The experimental results were utilized to calibrate and validate two prominent critical state-based models for unsaturated soils: the Barcelona basic model (BBM) and the Morvan model. While the BBM accurately predicted the deviatoric stress values at the critical state under controlled suction conditions, it did not adequately capture the postpeak softening behavior. Conversely, the Morvan model, after appropriate calibration and validation, successfully replicated both the critical state and postpeak behaviors, demonstrating a strong correlation between its predictions and the experimental data for both soil types.