Microscopic Mechanisms and Acoustic Emission Characteristics of Sandy Mudstone under Different Water Saturations

In order to study the damage mechanism of surrounding rocks under water-rock coupling, an experimental study on the microscopic law of water absorption and mechanics of sandy mudstone was carried out in the sandy mudstone stratum of Wanfu coal mine in Shandong, China. The results indicate that the strength of sandy mudstone exhibits three stages of relative softening, rapid softening, and decelerated softening. The speed of water molecules entering the microscopic pore structure was analyzed based on the percentage of water molecules in the pore structure. The acoustic emission energy release process is divided into energy accumulation stage, stable release stage and intense release stage. With the increase of water content saturation, Δα (Spectral width of the multifractal spectrum) tends to decrease and the distribution of events is gradually uniform. The action of water gradually expands and penetrates the cracks and pores inside the sandy mudstone, which makes Δf (Frequency of occurrence of the signal) change from negative to positive values.