Mechanical Properties and Acoustic Emission Damage Evolution of Sandy Mudstone Under Gradient Confining Pressures

Abstract

To reveal the macroscopic deformation failure and microscopic damage evolution mechanisms of sandy mudstone under deep high in-situ stress environments, triaxial compression tests were conducted under seven gradient confining pressures (0, 2, 4, 6, 8, 10, 15 MPa), and acoustic emission (AE) signals were monitored synchronously. The effects of confining pressure on the stress-strain characteristics, strength-deformation parameters, energy evolution, macroscopic failure modes, and AE damage laws of sandy mudstone were systematically analyzed. The results show that with increasing confining pressure, the compaction stage of the stress-strain curve disappears, the plastic stage prolongs, and the post-peak attenuation slows down, presenting a transition from brittle to ductile failure. The peak strength increases linearly with confining pressure, with a cohesion of 9.44 MPa and an internal friction angle of 29.44° fitted by the Mohr-Coulomb criterion. At low confining pressure, dissipated energy mainly drives tensile crack initiation, while at high confining pressure, it dominates shear crack development. AE activity is highly coupled with stress stages, and the cumulative ringing count reaches a peak at 10 MPa. The peak damage value decreases from 0.52 at 2 MPa to 0.12 at 15 MPa, indicating that confining pressure significantly inhibits damage accumulation. This study provides an experimental and theoretical basis for stability control of deep soft rock roadways.