Study on micromechanism of water absorption and its softening effect on shale rock in deep coal measures

Water absorption experiments under different water pressures were carried out on a series of shale samples collected from Shenyang of Liaoning province using a self-developed hydrophilic experimental system.At the same time,X-ray diffraction,high pressure mercury intrusion,scanning electron microscope and uniaxial compression experiments were performed on the shale rock samples before and after water absorption.The experimental results are as follows:① the absorbed water increases with time while the water absorption rate decreases with time and water absorption curves can be well fitted by an exponential function;② the water absorption capacities of the shale samples under different water pressures are remarkably different which are suggesting that water pressure can significantly increase the water absorptivity;③ the water absorption capacity and the clay mineral content are positively correlated which indicates that the clay minerals,specifically illite,plays an important role in water absorption process of the shale samples;④ the water absorption capacity and the effective porosity are negatively correlated and the reasons are closely related to a micro-structural perspective;⑤ the uniaxial compression strength(UCS)of the hydrated shale samples is negatively correlated with their water content and the increase of the porosity after water absorption may be an important reason for decreased strength of the hydrated shale samples.