Dynamic Rock Testing and Implications for Blast-Induced Ground Vibration Mitigation

ABSTRACT: mining requires continuous production through rock fragmentation by drilling and blasting. Drilling and blasting are essential to productivity but can result in blast-induced ground vibration issues in sensitive communities. Civil and geotechnical strategies considering rock structure and behavior under cyclic loading conditions can be used to predict ground vibration behavior and mitigate its effect. This study investigates key physics in cyclic dynamic wave propagation in rocks and provides fundamental results on dynamic wave propagation and attenuation in phyllite and granite under field-representative cyclic loading conditions. Supporting tests – x-ray diffraction (XRD) and porosity measurement are designed to characterize the physical and mineralogical behavior of the rocks. Uniaxial Compressive Strength (UCS) tests established the strong mechanical heterogeneity for both rocks and form the basis of the proposed mathematical model to predict each's monotonic rock strength. The mathematical model was developed based on the UCS to verify indicator points for subsequent cyclic experiments. Future work includes: (1) application of the mathematical model; (2) determination of wave propagation and attenuation in rocks under cyclic loading; and (3) investigation of coupling between rock damage accumulation and wave propagation. The experimental results are crucial to understand the fatigue process and predict rock behavior over time. 1. INTRODUCTION In order to liberate minerals in the mining process, blasting is conducted in a measured and controlled manner to expose orebodies for mechanical excavation (Darling, 2011). In mineral projects, the mining methods usually dictate the tools and explosives used to accomplish blasting. The mechanism of blasting breaks the continuum of the rocks for various mining purposes. In the instance of hard rock mining operations, production holes of a specific diameter and depth are drilled according to the mine plan and orientation of the orebody. Explosives used in blasting operations are selected based on several factors including the type and size of the ore zone, rock hardness, and the type of fragmentation required by the processing plant. Generally, drill and blast activities require the design of a drill plan comprising a boring of specified bedding and spacing for production holes in panels; loading of explosives (priming, stemming, emulsifying); attachment of detonators and delays, and subsequent detonation (manual or electric). The energy from blast detonation is primarily expended in rock breakage but some of the energy is wasted due to factors such as overcharging. This wasted energy travels from the blast site in the form of ground vibration and airwaves and dissipates in various forms including ground vibration, noise, dust, heat, and noxious gasses – giving rise to some undesirable environmental effects if not mitigated (Gad et al., 2005).