Evaluation of the dynamic shear strength of rocks under confininpressure

The shear strength of rocks is one of the significant parameters for designing geo-structures such as rock slope, tunnels, and underground space. This parameter has been widely applied for simulating rock fracture problems, which adopt a frictional failure criterion. In order to apply a shear failure model for simulating a dynamic fracture problem, it is essential to obtain the dynamic shear strength with increasing confining pressure. This paper presents the dynamic tri-axial punch shear test for evaluating the dynamic shear strength of rocks under confining pressure. In this method, a modified Hoek tri-axial pressure cell, which is applicable to split Hopkinson pressure bar (SHPB) system, was utilized to acquire confining pressure dependent dynamic shear strength. The investigation of dynamic shear strength was carried out with increment of constant confining pressure and loading-rate. It was found that dynamic shear strength increases with increasing confining pressure increment and considerably increases with increasing loading-rate. The value of cohesion also increased with loading-rate increment, while the internal friction angle remained constant. Finally, based on the experimental results, loading-rate dependent frictional dynamic failure criterion of rock was suggested.