Experimental study on the influence of water saturation state on the progressive failure characteristics in mudstone subjected stress loading

Abstract

Most studies on progressive failure in rocks have mainly focused on brittle materials, with limited attention given to mudstone, particularly regarding the effects of water. To address this gap, this study conducted mechanical tests on mudstone with varying water saturation, together with AE monitoring and SEM characterisation. The influence of water on physical state in mudstone was analyzed. The mechanisms by which water affects failure was revealed. The influence of water on progressive failure was discussed. Results indicate that, after water intruding mudstone develops tensile microcracks. Elastic modulus decreases linearly with saturation increasing. In mechanical tests, the proportion of AE tensile events and tensile cracking energy decrease linearly with water saturation, while plastic energy is the opposite. Macroscopic failure shifts from compressive shear to tensile rupture occurs with water saturation increasing. During the progressive failure process, crack initiation stress, crack damage stress, and peak stress all decreases exponentially with saturation increasing. While the uniformity of water distribution within the mudstone exerts a limited influence on both elastic modulus and P-wave velocity, it does effect on both stress threshold and progressive failure behaviour. After water intruding, the proportion of microcracking in elasto-plastic deformation stage (stage Ⅱ&Ⅲ) increases 20% average. Failure to account for the increased cracking behaviour into the elasto-plastic stage, may lead to overestimation of the long-term bearing capacity of mudstone in engineering application where potential leakage is a concern. This study provided a new insight into the long-term stability of mudstone under water intruding and stress loading.