Study on the Behavior of a Collapsible Soil under Constant Matric Suction Loading Implementing an Unsaturated Framework

Collapsible soils such as loess are usually found in arid and semi-arid regions. Catastrophic failure of residential building foundations due to wetting collapse is among problems associated with loessial deposits. This behavior is generally attributed to their open, unstable soil fabric and their weak inter-particle bonding forces, which together yield a void structured soil that is susceptible to collapse. In this study, one of the possible mechanisms of pore collapse (pore collapse induced by an increase in net confining stresses under constant matric suction, such as what occurs when a new structure is constructed on top of a collapsible soil deposit) is studied. In this regard, undisturbed unsaturated loessial soil samples have been obtained from the city of Gorgan, in Golestan province, Iran, and has been examined by implementing a full stress path controlled unsaturated triaxial apparatus at Sharif University of Technology that is modified to accommodate accurate unsaturated testing with automated continuous measurement of all required parameters. Based on the results of the tests, efforts are made to indicate the capability of a present constitutive model for unsaturated soils to predict the variation of yielding net confining pressure, and load-collapse curve (LC) for the examined collapsible soil. In this research, the present framework is modified to better predict the behavior of collapsible soils. The modification includes applying the effect of suction on the elastic constants. Applying the modified framework indicated a good agreement between the measured and predicted behavior of the tested collapsible soil.