Visualization and Characterization of Heterogeneous Water Flow in Double-Porosity Media by Means of X-ray Computed Tomography

Three-dimensional visualization of dynamic water transport process in soil by computed tomography (CT) technique is still limited by its low temporal resolution. In order to monitor dynamically water transport in soil, a compromise has to be found between water flow velocity and CT acquisition time. Furthermore, an efficient image analysis method is necessary. In this work, we followed the water transport in three dimensions by CT imaging across a double-porosity media constituted of two distinct materials, i.e. sand and porous clay spheres. The CT acquisition parameters were adjusted to the water pore velocity so that we succeeded to register the water front displacement per time range of 25 min. We also used the image subtraction method to extract water distribution evolution with time with a space resolution of 6× 10^-3 cm . Both time and space resolution are relatively high compared with other dynamic studies. The water content profiles showed that the clay spheres remained in their dry state during water infiltration, while the water transport only occurred in the sand matrix. These results are consistent with macroscopic experiments. The water front visualized by CT showed a non-symmetrical shape which was related to water transfer in non-equilibrium as shown by column displacement experiments.