Mechanical Properties and Fracture Mechanism of Pre-holed Rock under Impact Load

It is prone to occur dynamic disasters such as roof falling, sidewall slabbing and rock burst under dynamic disturbance of mechanical percussion drilling and explosive blasting in the roadway with hard rock. It is extremely meaningful to investigate the dynamic load effect on roadway deformation and failure mechanism. To understand the mechanical behavior of roadway surrounding rock under dynamic disturbance, a hard rock roadway was simplified as a hole in rock. And then, a series of impact tests were conducted on prismatic sandstone rock specimens with a hole by a modified split Hopkinson pressure bar testing system to explore the influence of hole size and shape on the dynamic mechanical properties, failure mode and energy dissipation characteristics. The results show that the existence of the hole has significant weakening effects on the dynamic strength, dynamic elastic modulus and peak strain. The dynamic mechanical properties of the rock decrease significantly with the increase of hole size. Among the specimens with different hole shapes, the dynamic strength and peak strain of the square-holed specimens are the largest, followed by the horseshoe-holed and the circle-holed specimens, but their elastic moduli show opposite results. In terms of rock failure modes, splitting tensile and tensile-shear failure occur respectively in intact specimens and pre-holed specimens under impact load. Additionally, the energy consumption density and fractal dimension of the horseshoe-holed specimens are the largest, which are 1.94 J/cm³ and 2.11 J/cm³, respectively. It indicates that the failure process is the most intense for the horseshoe-holed specimens, while the fragmentation degree of the circle and square holed specimens is not much different.