Behavior of compacted expansive soil under multi-directional stress and deformation boundary conditions

This study aims at investigating the effect of multi-direction stress and deformation boundary conditions on the volume change behavior of highly expansive compacted soils. Stress boundary condition refers to the stresses applied on the axial and lateral boundaries of the specimen. Deformation boundary condition refers to restraint imposed on the axial or lateral boundaries of the specimen. To this end, a series of response-to-wetting triaxial tests were carried out to simulate three boundary conditions; namely, constant isotropic stress (CIP), constant axial (CA) deformation, and constant volume (CV). In addition, a series of one-dimensional consolidation tests (oedometer tests) was performed to provide baseline information on volume change of expansive specimens under fully laterally restrained conditions. All tests, including the triaxial, axial stress and oedometer tests, were performed under a wide range of confining pressures, ranging between 50 and 800 kPa. Test results revealed that stress conditions had a significant effect on the magnitude and sign of strain realized during inundation of CIP and CA specimens. It was observed that axial restraint (in CA tests) or full restraint (in CV tests) induced time-dependent changes in stresses. In addition, this study demonstrated the effect of stress ratio, K, on the axial and volumetric swelling behavior of tested specimens. Finally, comparisons between triaxial and oedometer test results were conducted for realistic estimation of swelling strain under given boundary and stress conditions.