Understanding the effect of differential stress and fracture geometry on blast-induced damage in crystalline rocks: a numerical approach

This study employs numerical simulations to scrutinize the influence of pre-existing fractures and in situ stress states on blast-induced crack propagation in fractured rocks. The geomechanical behavior of fractured rocks is simulated via a particle-based discrete element model with particles constructed and assembled by the Voronoi tessellation scheme based on the grain-size distribution of actual rock samples (specifically, Beishan granite), which captures solid vibrations under dynamic loading and realistically responds to crack growth and fracture displacement. The reliability of the model is also validated using Snell’s law and fracture mechanics. Based on the model, the effects of stress states and fracture configurations (such as single isolated fracture and two interacting fractures) on damage evolution are examined. It was observed that when the differential stress is aligned (or perpendicular) with the blasting wave, it amplifies (or reduces) the damaging effect of the blasting wave on the rock mass in most instances. The effect of the differential stress on the blasting wave is similar to that of an increase (or reduction) in the amplitude of the blasting wave. When the differential stress exceeds the tensile cracking stress, rock damage sharply escalates due to the generation of a plastic region, regardless of the angle between the blasting wave and differential stress. Meanwhile, a study of two interacting fractures reveals that differences in fracture geometry lead to different stress concentration and shadow zones in the specimen. This changes the location and extent of crack development and ultimately affects the strength of the rock. The findings from our simulations provide critical insights for understanding and characterizing excavation damage zones around underground excavations in fractured crystalline rock obtained by drilling and blasting methods and also provide safety predictions for constructed neighboring structures under dynamic loads.