Study on sandstone creep properties of Jushan Mine affected by degree of damage and confining pressure

Creep characteristics of rock mass are related not only to the confining pressure but also to the degree of internal fracture damage. Revealing the creep characteristics of rock mass under different confining pressures and degrees of damage is of great significance for selecting a reasonable supporting time and optimum supporting strategy in engineering. Sandstone is the main medium of the coal seam roof in the Jushan Mine and has poor physical and mechanical properties. To study the creep behavior of sandstone, triaxial creep tests and simulations are conducted under different confining pressures and degrees of damage. The results show that the appearance of the creep stage is related not only to the stress but also to the confining pressure and the degree of damage. With an increase in the confining pressure or the degree of damage, the creep parameters will have clear change, especially under high stress level. The creep parameters and confining pressures show different changing laws, and there are also different relationships between the creep parameters and the degrees of damage. Three surface equations are proposed to visually describe the variation in the creep parameters with the confining pressure and the degree of damage. The sudden increase in cracks is affected by both the confining pressure and the degree of damage, and it can be used as an early warning of rock failure. Thus, the influence of the confining pressure and damage should be simultaneously considered in the long-term stability of rock mass.