Dynamic strength characteristics of fractured rock mass

Abstract

Fractures play crucial role in the behavior of rock masses, yet the understanding of their natural distribution and impact on dynamic characteristics remain unclear. Here the effect of “natural” fractures on the dynamic impact strength of rock mass was investigated using numerical specimens with fractures prepared using the Split Hopkinson Pressure Bar (SHPB) model. These fractures were generated through biaxial compression simulation. Various axial stress levels and confining pressures replicated diverse natural rock fracture distributions. To capture the anisotropic distribution of fractures in natural rock and the randomness of impact direction, impact from 0°, 90°, 180° and 270° directions were imposed. The biaxial loading simulation showed that fracture increases with higher loading stress, and rapidly expands in the post-peak stress stage, with ∨ or ∧ shaped slip plane depending on confining pressure. The impact strength of the fractured specimen decreases as the number of prefabricated fractures increases, following a two-stage pattern, i.e., rapidly decrease with small number of fractures and gradually decrease with high number of fractures. Pre-existing fractures aligning with the impact direction provide stronger resistance compared with fractures deviated, and their location and distribution significantly affect the stress transmission. The impact from other directions has different stress transmission routes related to the fracture and macroscopic surface distribution. Importantly, a specimen’s loading history shapes its internal fracture distribution, thereby affecting its resistance to impact stress. This research provides invaluable insights into the role and mechanics of fractures in rock masses, thus enhancing our understanding of rock dynamics and potentially informing more effective geotechnical engineering practices.