Evaluation of distribution of void ratio and degree of saturation in partially saturated triaxial sand specimen using micro x-ray tomography

Partially saturated soils are composed of three phases: soil particle, pore water and pore air. The pore water forms menisci among soil particles at which suction works. Suction is higher at the upper part of partially saturated soils due to the higher negative pressure head. It is therefore likely that degree of saturation in partially saturated soils distributes in a vertical direction with different suction levels. Additionally, partially saturated soils show more brittle mode of failure compared with fully saturated soils for which investigation of distribution changes in degree of saturation and void ratio is important. In this present study, triaxial compression tests for partially saturated Toyoura sand specimens are conducted and x-ray computed tomography scans are performed at initial state and after tests. Trinarisation technique by taking into account partial volume effect is applied to evaluate the volume of each three phase, through which the distribution of void ratio and degree of saturation in a vertical direction of partially saturated trixial sand specimens are discussed. It is found that degree of saturation is lower in larger voids while degree of saturation was higher in smaller voids. At the middle of specimen where large deformation is observed, void ratio and degree of saturation significantly changes while those at the other position where less deformation is observed slightly changes.