Fracture propagation and permeability evolution mechanism of jointed rock mass in coastal mines

To study the fracture propagation mechanism and the permeability evolution of the fault fracture zone in coastal deep mines, the nuclear magnetic resonance (NMR) tests and the triaxial mechanical properties tests of rock specimens rock mass specimens with different joint dip angles under hydro-mechanical coupling were carried out. Based on the investigation of the surrounding rock joints and the analysis of rock composition, the rock physics experimental model was prepared. The evolution mechanism of rock porosity is obtained by NMR test. The changes of mechanical properties, acoustic emission (AE) and permeability characteristics of rock specimens with different joint dip angles were studied, and the evolution mechanism of permeability properties with different joint dip angles is revealed by combining the microstructure and joint tip expansion mechanism. When the jointed rock mass specimens reach the peak stress, the bearing capacity of the specimens decreases slowly, and the specimens show the characteristics of progressive failure. The specimen generates micro-cracks at the joint tip under the action of axial pressure, micro-cracks evolve and expand with the increase of pressure, the permeability coefficient gradually increases. The main fracture of jointed rock mass specimens is the fracture that originates from the joint tip and extends along the axial direction until the specimen loses its bearing capacity.