The shear strength of rocks is crucial when designing geo-structures, such as rock slope, tunnels, and underground space. Many researchers have suggested methods for determining the shear strength of rocks and concrete using a direct shear-box test, punch shear test, etc. In order to use the shear strength as an input parameter for simulating dynamic fracture problems that adopt a frictional failure criterion, it is necessary to obtain the dynamic shear strength with increasing normal stress.
In this study, a modified Hoek tri-axial cell, which is applicable to the Split Hopkinson Pressure Bar (SHPB), was suggested to obtain confining pressure dependent dynamic shear strength. The dynamic shear strengths were determined in increments of constant confining pressure and loading rates. Our findings show that dynamic shear strength increases with increasing confining pressure and significantly increases with loading rate increments. The value of cohesion also increased with increasing loading rate, while the internal friction angle remained constant. Validation of the suggested loading rate dependent frictional dynamic failure criteria of a granite rock is discussed.