Micro-Mesoscopic Creep Damage Evolution and Failure Mechanism of Sandy Mudstone

Abstract

A typical sandy mudstone from the deep-buried roadway of the Kouzidong coal mine was taken as the research object. Based on the micro-mesoscopic experiments combining the acoustic emission (AE) and digital speckle correlation method (DSCM), as well as numerical simulations based on the discrete element method (DEM), both the micro-mesoscopic creep damage evolution and the failure mechanism of sandy mudstone were investigated. The experimental results show that the AE curve of sandy mudstone in the multilevel creep test is consistent with the axial strain curve. Three stages, including the decelerative, isokinetic, and accelerative creep stage, can be identified. The three-dimensional source location of AE events shows that the creep loading leads to more severe, homogeneous, and dispersed microdamage in sandy mudstone and a looser failure mode. It was also found by DSCM techniques that the microscopic deformation field evolution of sandy mudstone in the creep process well corresponds to the three stages of creep failure. A transition of microscopic deformation field from random, via symmetrical, to asymmetrical distribution, can be observed during the creep failure process of sandy mudstone. By introducing the time-dependent stress corrosion theory into the existing parallel-bonded model (PBM) in particle flow code (PFC), the microdamage evolution mechanism of sandy mudstone under creep loading was studied both theoretically and numerically, and the corresponding results revalidate our experimental findings.