Effect of axial static stress on mechanical properties of post-peak cracked sandstone under impact loading

The surrounding rock mass in deep engineering is always in the post-peak state and suffers the influence of dynamic disturbance. The impact compression experiments on post-peak cracked sandstone samples were carried out to investigate the dynamic mechanical properties of cracked rock under one-dimensional coupled static and dynamic loads by using modified split Hopkinson pressure bar (SHPB) apparatus. The axial pre-compression stress was respectively set as 8,24 and 48 MPa,and the impact loading was carried on to investigate the effect of axial static stress on the me- chanical properties of post-peak cracked sandstone under different strain rates. Compared with intact sandstone results, the results show that under the axial static stress of 8 MPa and the similar strain-rate,both the combined strength and the impact strength of post-peak cracked sandstone are lower than that of intact sandstone,and the deformation modu- lus is essentially the same,but the absorbed energy per volume of post-peak cracked sandstone is higher than that of intact sandstone. Under the same axial static stress,both the combined strength and the impact strength of post-peak cracked sandstone increase with the strain rate increasing. Under the different axial static stresses, the combined strength increases with the axial static load increasing,while the impact strength increases first and then decreases. Ax- ial static stress has an effect on the absorbed energy per volume of post-peak cracked sandstone,and the absorbed en- ergy per volume increases with the increase of axial static stress. The post-peak cracked sandstone is shear failure sub- jected to the coupled static and dynamic loads,and the original crack influences on the crack propagation direction during the process of impact failure.