Experimental and Numerical Investigation into the Fracture Patterns Induced by Blast-Loading Under Unconfined and Confined Conditions

This study analyzes the fracture patterns generated from the high-energy release caused by commercially available explosives and the current capability of numerical methods to replicate this. The mechanics of rock fracture and fragmentation are first studied using the Hybrid Stress Blasting Model (HSBM) at the lab-scale through comparison with experimental results available in the literature. Following this, an in-house experimental blast campaign was undertaken with a detailed examination of an unconfined, 605 mm diameter cylindrical sample and a pressurised (confined), 700 mm diameter cylindrical sample. The post-blast samples were dissected and fractures were visually mapped before comparing the fracture intensity results to the output of the HSBM, which captures stress-wave-induced damage but not gas loading, for these test cases. This paper makes contributions to the literature in three fundamental areas. Firstly, the capability of numerical methods to capture the phenomenology of blasting on rock fracture and fragmentation was validated and the limitations were discussed when looking to use this as a design tool for practical blasting operations. Secondly, the experimental campaign provides detailed insights into the response of cementitious grout materials to internal, blast-induced loading that can be applied in various fields such as mining and construction. Finally, the impact of confining pressure on blast damage was investigated and details were provided for how this can be captured in numerical predictions. It was found that certain aspects of the material response can be well predicted through numerical analysis, namely, the damage radius and the number of dominant fractures. However, it also indicated a shortcoming in the explicit comparison of fracture intensity measures such as P21, with the use of damage metrics appearing more appropriate. The grout-based testing methodology discussed in this work provides an efficient means for gathering data on the impacts of individually controlled aspects of a blast in both unconfined, and confined environments.