Unified Consolidation-Creep-Collapse Phenomena in an Unsaturated Sand-Bentonite Mixture

Unsaturated soils that exhibit significant volume reduction under wetting or mechanical loading are referred to as collapsible soils. The main objective of this study is to investigate the time-dependent response of an unsaturated sand-bentonite mixture under coupled hydromechanical loading conditions. For this purpose, a modified osmotic oedometer device was employed to determine soil volume change properties such as the compressibility coefficient, creep index, and collapse potential under controlled matric suctions. The results demonstrate the interaction of the stress history and the long-term behavior of the tested soil, suggesting that creep and consolidation deformations strongly depend on the preceding hydraulic loadings. Incomplete collapse incidents were observed in the specimens confined in the oedometer ring in which the specimens did not collapse laterally. As a result, the volume states of the collapsed samples were located above the saturated normal consolidation line. The higher void ratios led to higher creep deformations in saturated samples that experienced the collapse phenomenon. This behavior is attributed to the meta-stable condition of samples, which eventually tends to evolve toward the stable virgin consolidation curve. Moreover, the creep index and collapse potential increased with the net stresses within the range of applied loads. Findings confirm the reverse relationship between the creep index and applied matric suction.