Experimental study on the microscopic swelling-shrinking mechanisms of clay-sand mixtures from wetting to drying

Abstract

Micro-computed tomography and low-field nuclear magnetic technologies were employed to investigate the evolution of the water occurrence and particle behaviors of the montmorillonite-kaolinite-quartz sand mixtures along a wetting-drying cycle. During the wetting-drying process, the total saturation was linearly related to the sample height. The cutoff values between the adsorbed water, capillary water and bulk water were roughly determined as 2.5 ms and 50 ms, respectively. In the wetting stage, the swelling under lower water content was dominated by adsorbed water, but it mainly depended on the linear increase in capillary water under higher water content. In the drying stage, the water distribution along the height was divided into apparent dry region, capillary flow region and saturated region. With continuous drying, the first region gradually expanded and the second reduced. Compared with nondeformable porous media, the range of them was smaller. If further dried to 5% water content, there will be only adsorbed water. The capillary water content was found to be linear with the sample height during drying. Consequently, the inconsistency of swelling-shrinkage deformations was mainly attributed to the hysteresis of capillary water. This work will provide basic experimental data and guidance for the subsequent simulations and theoretical model.