Experimental Investigation on the Influence of Thermochemical Effect on the Pore–Water Status in Expansive Soil

The pore-water status, including adsorptive and capillary water, in expansive clay with different dry densities was investigated under the effect of temperature and saline solution via the nuclear magnetic resonance technique. Combined with a method of distinguishing the adsorptive and capillary water, the variations in the adsorptive water content with the thermochemical effect were obtained quantitatively. The experimental results show that the adsorptive water content decreases as the temperature increases, consistent with the theoretical conclusion, which is considered to be attributed to the increase of the chemical potential and the activity of the pore water. On the other hand, the volume of micropores decreases while the volume of macropores increases with the increasing temperature or concentration, resulting from the flocculation and agglomeration of soil particles. Meanwhile, the increase of salt concentration can suppress the electric double layer and decrease the micropore volume, resulting in a decrease in the adsorptive water content. In addition, due to ion hydration, the relaxation of water molecules accelerates, shifting the water distribution curves of soil leftward as concentration increases. This effect overshadows the suppression of electric double layers and the decrease of the micropores, rendering higher adsorptive water content. The microstructure and the pore size distribution, obtained by the scanning electron microscope and mercury intrusion porosimetry experiments, were used to validate the variation of the adsorptive and capillary water in the pores.