X-ray tomographic method for measuring three-dimensional deformation and water content distribution in swelling clays

Abstract

A non-invasive method for simultaneous measurement of the 3D displacement field and the water content distribution of a wetted solid material is developed. The method is based on comparison of X-ray tomographic images of a material sample in the reference state and in the wetted and deformed state. The deformation and water content analyses were successfully compared with numerical results for a cylindrical rubber test sample under axial compression, and with gravimetric results from axially wetted and sliced cylindrical bentonite samples, respectively. The methods were applied in a 4D study (three spatial dimensions and time) of wetting and deformation of purified swelling bentonite doped with glass tracer particles, and wetted with synthetic groundwater. The results obtained for bentonite samples are repeatable and appear qualitatively correct and plausible. They are useful e.g. in validating models involving transport of water and the resulting swelling deformation of bentonite. The method is potentially applicable also in other processes involving liquid transport and deformation such as wetting/swelling and drying/shrinking of heterogeneous materials. A prerequisite for the applicability of the method is that the material contains sufficient amount of local inhomogeneities visible and identifiable in successive tomographic images to facilitate deformation analysis, and that change in water content affects the total density enough to be observable in X-ray images.