Mesoscopic Damage Mechanism of Red-bed Mudstone Based on Geometric and Mechanical Representative Elementary Areas

The utilization of mesoscopic representative element areas (mREA) is crucial in providing a more comprehensive elucidation of the impact of the intricate mudstone mesostructures on their failure mechanism. Conventional methods for estimating the mREAs are laborious and lack of assessing their mechanical behaviors. Based on the mean structural similarity, this paper proposed a pair of mREAs, i.e., the most representative region (MRR) and the most special region (MSR), to describe the characteristics of mudstone mesostructures jointly. The mechanical behaviors of the MRR-MSRs and their mesostructures were then investigated to reveal the mesoscopic damage mechanisms and verify the representability of the MRR-MSRs. Results showed that the fractures in the MRR-MSRs originated from the porous matrix sides of the inclusion-matrix interfaces. For the mesostructures, the fracture propagation was primarily influenced by the connectivity of the inclusion-matrix interfaces and the distribution of the porous matrix regions. Particularly, the mesostructure gradually showed a layered shear failure mode as the content of the nonclayey minerals increased. However, the characteristic length of mudstone's mechanical mREA (mech-L_REA) was smaller than that of the geometric mREA (geo-L_REA) due to the limited influence of captured pores. These results provided new insights into the mesoscopic damage mechanism of argillaceous rocks.