Dynamic mechanical properties and failure behaviors of brittle rock materials with a tunnel-shaped opening subjected to impact loads

Since the surrounding rocks of underground tunnels are frequently suffered from the dynamic disturbance of mechanical percussion drilling and explosive blasting, it is significantly meaningful to investigate the mechanical properties and failure behaviors of rock material with a tunnel-shaped opening under dynamic loads. In this work, seven groups of prismatic samples, including the intact samples and the samples with a circular opening of three kinds of diameters, a square opening, a horseshoe-shaped opening and a D-shaped opening, were prepared for dynamic compressive loading. The results show that the prismatic specimens satisfy the stress uniformity condition in impact tests using SHPB testing system with a bar diameter of 50 mm. The weakening effects of the existed openings on the dynamic compressive strength, elastic modulus and peak strain of rocks are closely associated with the size and shape of opening and the loading direction. Based on the energy parameters of the samples, the dissipated energy density of each group of samples can be solved. The failure degree of the samples characterized by dissipated energy density and fractal dimension are in good agreement. Besides, the failure mode of the intact specimen belongs to splitting tensile failure, while that of the pre-holed specimens can be classified as shear-dominated failure due to the coalescence of the openings and the shear cracks occurring along the diagonals of the specimens. The test results provide some insights into the mechanical behavior of rock materials under dynamic loads and lay an important theoretical foundation for support design and rock disaster prevention of underground tunnel.