Deformation Behavior of Unsaturated Soils

Project Overview
A recent project sponsored by a MURI grant from the Office of Naval Research (ONR) (grant N00014-11-1-0691) has focused on understanding the mechanical behavior of unsaturated soils under conditions related to buried explosives. Woongju (MJ) Mun is studying the compression behavior of unsaturated soils under isotropic stresses up to 160 MPa. Jenna Svoboda, Mehmet Can Balci, and Thayza Teixeira have studied the impact of shearing rate on the shear strength of unsaturated soils. MJ also worked with Fabricio Valente to study the compression behavior of sand-clay mixtures. We are collaborating with researchers from other universities to integrate our work on soil behavior into the prediction of blast pressures and ejecta distribution related to a buried explosive. 

Previous Work on this Topic
Several researchers in our group have focused on understanding the fundamental properties governing the deformation response of unsaturated soils. Ali Khosravi and Majid Ghayoomi performed a series of tests to characterize the role of stress state on the dynamic shear modulus of unsaturated compacted soils. Ali Khosravi developed an approach to control the suction and track changes in degree of saturation within a soil specimen inside a resonant column-torsional shear cell, which permitted an understanding of the impacts of hydraulic hysteresis on the shear modulus. Ali worked with Chris Lynch and Nahed Alsherif to perform a series of staged triaxial tests on unsaturated, compacted silt, which helped us define the suction-stress characteristic curve for the silt. This information was being used to complement Ali's research findings on the definition of a single-value effective stress in unsaturated silt. Nahed performed a series of triaxial compression tests on unsaturated silt at high pressures and high temperatures. She used the vapor flow technique to control the suction magnitude in compacted silt specimens, and has observed a complex combination of hardening during suction application and softening during heating.  Majid Ghayoomi evaluated the seismic response of partially saturated sand layers using a novel geotechnical centrifuge test. He used steady-state infiltration of water to control the degree of saturation in a sand layer, then performed cyclic shaking tests. Majid used this setup to provide validation data for a semi-empirical model to predict the seismic compression of sand layers having different degrees of saturation.