Theoretical and Experimental Study on Single Spherical Button Penetration into Granite Rock Under Dynamic Impact Loading

It is of great significance to reveal the penetration damage behavior of hard rock under confining and hydrostatic column pressure for improving the rate of penetration of percussion drilling. In this paper, experiments of single spherical button penetration into granite rock under dynamic impact loading were conducted. The cavity expansion model (CEM) was utilized to predict the radius of the elastic–plastic boundary and compared with the experimental results. The essential parameters of the crater were tested and analyzed, and the damage of the sample was evaluated. The quantitative study of crack and damage zone revealed the failure mechanism. The results indicate that both confining pressure and hydrostatic column pressure have adverse effects on the damage of hard rock, but confining pressure is the dominant factor. The change of fractal dimension is mainly caused by the transformation of crack type. The radius of the elastic–plastic boundary reveals that confining pressure can enhance the strength of the rock, shorten the length of the radial crack, and increase the difficulty of lateral crack propagation to the free surface. Although hydrostatic column pressure can aggravate the internal damage of the rock, the lateral cracks cannot extend to the free surface to form radial cracks due to the distant location of the lateral crack initiation, which makes it impossible to form a large crater.