STUDY OF STRAIN LOCALIZATION AND MICROSTRUCTURAL CHANGES IN PARTIALLY SATURATED SAND DURING TRIAXIAL TESTS USING MICROFOCUS X-RAY CT

It is well known that strain localization and microstructural changes are important issues in the onset of failure problems. In particular, unsaturated soil exhibits more brittle failure due to the collapse of the water meniscus, caused by shearing or the infiltration of water, than saturated soil. The aim of this paper is to observe the strain localization behavior and the microstructural changes in partially saturated soil during the deformation process using microfocus Xray CT. The micro focus X-ray CT system employed in this study has a very high spatial resolution of 5 mu m, which is enough to visualize the sand particles and the other particles individually. In addition, X-ray CT scans can be performed under triaxial conditions. The strain localization of fully saturated, partially saturated, and air-dried sand specimens during triaxial compression tests is observed and discussed. The microstructure of unsaturated soil, consisting of soil particles, pore water, and pore air, is successfully observed in partial CT scans. Through a comparison of the microstructures in the shear bands and in the initial state, the microstructural changes are discussed.