Experimental investigation of the mechanical behaviors and energy evolution characteristics of red sandstone specimens with holes under uniaxial compression

To explore the mechanical behaviors and energy evolution characteristics of rock materials with hole defects, eight types of red sandstone specimens with different hole numbers and arrangements were subjected to a series of single-cycle loading-unloading uniaxial compression tests. The experimental result revealed that the mechanical behaviors and energy evolution characteristics of the red sandstone specimens are significantly influenced by hole defects. As the number of boreholes increases, the compressive strength of rock specimens decreases. When the angle between drilling hole arrangement and loading direction changes from 0 degrees to 27 degrees and then to 90 degrees, the compressive strength first decreases and then increases, and shear-splitting, splitting, and shear failure modes appear respectively. The experimental results also show that the energy evolution characteristics (linear energy storage and dissipation laws) of the rock specimens with hole defects were basically consistent with that of intact rock specimens, while the energy storage coefficient is different in various cases. There was a good correspondence between the compressive strength and energy storage coefficient. The larger the energy storage coefficient is, the greater the compressive strength. The hole arrangement angle shows a stronger effect on energy storage coefficient and compressive strength than the number of holes. Among all the arrangements, the rock specimens containing three holes with an angle of 27 degrees between borehole arrangement and loading direction have the lowest energy storage coefficient and compression strength. The above research results provide a scientific basis for rock fracturing induced by drilling.