A study of the acoustic emission and fractal damage of sandstone under the coupling of seepage and stress

Mechanical properties of rock under seepage-stress coupling are important in mine engineering. In order to explore the evolution of the internal micro-hydro rock damage force under coupling of mine engineering from a sandstone, three axial penetration and acoustic emission tests are conducted. The results show that the change in permeability of the sandstone includes four stages: decrease, dynamic balance, rapid increase and slight decline. The acoustic emission phenomenon is characterized by a periodic change, and the greater the confining pressure is, the more the acoustic emission is lagged. Fractal characteristics based on the columnar fractal theory show that the fractal dimension decreases gradually. The results also show that the internal damage of the sandstone has experienced a change from disorder to order, and the emergence of the fractal dimension can be used as a precursor to the failure of the sandstone. The damage value of the sandstone under seepage-stress coupling increases exponentially, and the seepage damage Ds mainly concentrates on the yield stage. The ratio of the osmotic damage to the total damage decreases linearly with the increasing confining pressure. Stress loading is the main factor of the sandstone damage and the osmotic damage is a secondary factor. The fractal dimension df has a good negative exponential function with the damage D and the osmotic damage Ds.