Deterioration of mudstone exposed to cyclic hygrothermal conditions based on thermoacoustic emission

The periodic effect of an alternating hygrothermal environment makes the microdamage of rock gradually accumulate, thus leading to significant structural damage. The study of the progressive deterioration of mudstone exposed to cyclic hygrothermal conditions is of guiding significance to the stability of bank slopes. In this paper, purple mudstone samples from the Three Gorges Reservoir area were collected for laboratory cyclic hygrothermal experiments. Thermoacoustic emission tests of mudstone samples with different water absorptions under multiple hygrothermal cycles were carried out, and the influence of water content on the macroscopic surface damage and acoustic emission (AE) characteristics of mudstone was analyzed. The results show that the AE counts of mudstone with various water absorptions during heating can be divided into three typical stages of AE activity: active, intense and quiet. The active period of AE activity corresponds to mudstone surface temperatures of 35–50 ℃, which is considered to be the temperature range most likely to induce damage: fracturing, spalling and disintegration. The gradual increase in water absorption of mudstone leads to a decrease in the cumulative AE count during heating as the number of hygrothermal cycles increases, indicating that more clay minerals in the mudstone absorb water and undergo inhomogeneous deformation during each hygrothermal cycle, so that a large number of microcracks or even a network of cracks have been developed in the process of water absorption. This understanding of the deterioration of mudstone provides evidence for the assessment of mudstone strata stability.