Test and analysis of sandstone damage-weakening under loading- unloading-loading

In order to investigate the weakening law of rock mass mechanical properties in the whole process of deep roadway surrounding rock excavation,the sandstone specimen tests of uniaxial loading with different loading rates,tri- axial loading with different confining pressures and triaxial loading-unloading-uniaxial loading with different degrees are carried out to study the damage and the weakening mechanism in the process of loading,unloading and loading. The results show that there is a power function between the peak strength and the loading rate,and a linear relationship with the confining pressure. The higher the loading rate and confining pressure are,the higher the strength of sandstone specimens is. The ultimate failure mode of sandstone in the triaxial loading-unloading-uniaxial loading is not related to the loading history,but is related to the ultimate stress state of rock. The ultimate strength of rock is bound up with the loading rate,confining pressure and loading and unloading disturbance of loading history. The larger the initial axial pressure and the initial damage are,the smaller the ultimate strength of the unloading and loading is. In addition,the rock damage index based on the energy density and the strength weakening calculation method based on the state of the loading process are put forward,which is proved to be feasible by the calculation.