Interaction Between Water and Soft Rocks

Abstract

Water sorption is one of the most important causes for rock deformation and failure. Liquid and gaseous water adsorption experiments were carried out on shale, conglomerate and soft rock samples. First, water absorption experiments under different water pressures were carried out on a series of shale samples collected from a deep coal mine in China. The experimental results showed that the absorbed water increases with time while the water absorption rate decreases with time. Comparison between the water absorption capacities of the shale samples under different water pressures suggested that water pressure significantly increases the water absorptivity. Second, water vapor sorption experiment was carried out on clay-bearing conglomerate rock samples collected from northeast China to investigate dynamics of water vapor sorption and vapor-induced strength softening effect. The experimental results have shown that the amount of water vapor sorbed by each conglomerate sample kept increasing with time until finally reached to a plateau, generally following an exponential law. Negative correlations between water content and uniaxial compressive strength (UCS) as well as modulus of elasticity suggested that with increasing water content induced by vapor sorption conglomerate rock strength tended to decrease, and meanwhile it was more prone to deformation. Furthermore, microstructure images of scanning electron microscope (SEM) analyses for conglomerate rocks before and after water vapor sorption showed that after vapor sorption conglomerate rocks have undergone significant changes in microscopic morphology which may be an important cause for rock softening and deterioration. Third, X-ray diffraction analysis (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 clay-bearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and water-induced strength degradation effect of the investigated deep soft rock samples. Water vapor absorption processes of all the soft rock samples follow an exponential law. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples.