Multi-scale correlation analysis of acoustic emission characteristics and energy evolution process of cavernous fractured sandstone

To investigate the load-induced fracture instability of cavernous fractured sandstone under varying hole diameters and fracture dips, uniaxial compression tests were performed on red sandstone samples from the Linyi mountainous area. Based on the minimum energy theory and the hard body hypothesis, the stress-strain curves, energy evolution laws, and AE characteristics of different specimens were analyzed. The results show that fracture propagation and coalescence lead to the instability and failure of sandstone, and the mechanical properties of the sandstone differ with varying hole diameters and fracture dip angles. The stress of sandstone first decreases and then increases with the fracture dip angle. An increase in hole diameter reduces the stress, but the magnitude of reduction is small. The strain exhibits an "M"-shaped variation pattern with the fracture dip angle. The strain energy of sandstone during loading shows a pattern of slow increase, rapid increase, and post-peak stability. With the increase of fracture size, the strain energy first decreases and then increases. The AE energy during sandstone loading increases intermittently, and a "quiet period" phenomenon is observed before reaching the peak stress. The AE energy is greatest after failure. The relationship between AE energy and strain energy follows a power function. A hypothesis for the disturbance-induced instability failure of fractured rock masses was proposed: after the fracture of the hard body, disturbance leads to the instability failure of sandstone in a self-organized critical state. This was validated through AE localization and the actual fracture propagation patterns. The research findings hold significant theoretical and practical value for stability monitoring, early warning, and disaster prevention and control in fissured sandstone.