Dynamic magnification of strainburst demand by soft loading system stiffness in synthetic hard brittle rock specimens

This is the authors' abstract. We don't add key points for this paper.

Deep hard-rock mines may develop progressively softer loading environments as extraction advances, particularly near cave footprints, and highly stressed excavation boundaries. Under these conditions, brittle collapse may shift from a material-controlled failure process to a system-controlled instability driven by excess elastic strain energy released from the mine loading system. Although very stiff testing machines are essential for capturing the characteristic post-peak behaviour of brittle rock, they do not reproduce the softer loading conditions that commonly govern dynamic damage in mining environments. Numerical experiments using the discontinuum code PFC2D were conducted to investigate how loading system stiffness (LSS) influences the post-peak response of unsupported synthetic hard brittle rock. The model setup was first verified to confirm the global force–displacement response. Quasi-static and dynamic uniaxial compression simulations were then performed under different LSS conditions to quantify post-peak behaviour and damage magnification during dynamic brittle collapse. The results show that intrinsic rock properties primarily govern the response under stiff LSS conditions, such as isolated tunnel advances. Under soft loading, as may occur during late-stage extraction or near cave footprints, excess elastic strain energy from the LSS becomes increasingly influential and magnifies specimen-scale strainburst intensity (ejection velocity of breakout formations), severity (ejected mass at test termination), and bulking response (stress-induced fractured ground). The characteristic specimen-scale rupture duration for localized fragment ejection ranges from 0.10 to 0.22 ms. These sub-millisecond values reflect the small, mobilized volume and low inertial resistance of the unsupported specimen and should not be directly extrapolated to excavation-scale strainburst durations.