Modeling Unsaturated Soil Response under Suction-Controlled True Triaxial Stress Paths

Results from a comprehensive series of suction-controlled hydrostatic compression, conventional triaxial compression, triaxial compression, triaxial extension, and simple shear tests, conducted on statically compacted specimens of poorly graded sand with clay, are presented. The experiments were accomplished in a newly developed true triaxial apparatus to test cubical, 7.62 cm (3 in.) side, specimens of unsaturated soil under controlled-suction states and for a wide range of stress paths that are not readily achievable in a cylindrical cell. The key features of the apparatus and a thorough performance verification test program have been documented in a first companion paper. Results from suction-controlled tests performed in the present work were used to calibrate and further validate two of the most popular elastoplastic critical state-based frameworks postulated to date for unsaturated soils, namely, the Barcelona Basic Model and the Oxford Model. In general, predictions of unsaturated soil response from either model are shown to be reasonably accurate, highlighting their potential for use in computational analyses of geotechnical boundary-value problems that involve geosystems made of compacted soil or resting on unsaturated ground.