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ABSTRACT: Simultaneous detonation of charges in closely spaced boreholes is a commonly used blasting technique for frag-mentation and construction. Blasting is a challenging phenomenon to model, due to the complexity of the mechanical deformation, fracturing, and fragmentation, and the spatial scales involved. Blast wave models must consider the possibility of constructive interference between separate waves in three-dimensions. A three-dimensional finite element method is used to study the induced damage in a general hard rock tunnel blast setting. The Johnson Holmquist-2 elastoplastic-damage model is used to quantify shear and tensile failure. In simulations with two blastholes separated by up to one meter, damage patterns emanating from boreholes interact to form self-organizing ‘fracture-like’ structures. Mechanical interaction between the two blasts is a function of the input charge wave properties, blasthole separation, and distance along the charge, with high concentrations of damage at the free boundary representing the tunnel wall. Constructive interference between the two blast waves is not shown to directly induce additional damage zones, and instead, interaction results from the overlap and slight extension of each blasthole’s damage zone towards the other. 1 INTRODUCTION Drilling and blasting continues to be a key method for mining and excavation (Lu et al., 2012). Many blasting applications, such as bench blasting or tunnel excavation, involve drilling and blasting multiple holes in close proximity to one another in order to generate overlapping fractured zones (Cho and Kaneko, 2004). Efficient use of explosives reduces costs, improves sustainability, and ensures that the extent of the excavation disturbed zone is minimized, the latter being an important constraint for the construction of radioactive waste disposal facilities (e.g., Tsang et al., 2005; Kwon et al., 2009) and many civil engineering projects (e.g., Sharafat et al., 2019). Due to the complex physics of blasting and rock fragmentation, a fully mathematical description of the process is not possible, and blast operation designs often make use of empirical formulas (Liqing and Katsabanis, 1997). In particular, the dynamic weakening (damaging) of rock introduces challenges for models, and upscaling of damage is necessary to avoid resolving the complex geometry of fracturing and fragmentation. Numerical approaches are therefore used widely to understand the process of blasting (e.g., Liqing and Katsabanis, 1997; Yilmaz and Unlu, 2013; Yang et al., 2015; Hajibagherpour et al., 2020; Ji et al., 2021; Pu et al., 2021). |
