Severe seismic events often take place in a fault damage zone away from active mining areas, even though the mining-induced stress change is negligible in the region. The objective of this study is to elucidate the mechanism of such burst-prone stress conditions being generated in a fracture network within a fault damage zone. Numerical analysis results indicate that extremely high burst-prone potential is locally generated in the fault damage zone because of the spatial heterogeneity of the rock mass stiffness. That is, a local zone with a lesser fracture density has a high elastic modulus, whilst high fracture density decreases the apparent elastic modulus of the region. The difference in the rock mass stiffness yields extremely high stress concentrations when subjected to reginal stresses due to plate tectonics. Specifically, the maximum stress in a stiff zone can be four to five times that of the zone with low elastic modulus. This result cannot be obtained from conventional (continuum) numerical modelling techniques for deep underground mines that predominantly ignore the heterogeneity of rock mass stiffness and its effect on pre-mining stress state. The study successfully reproduces pre-existing stress anomalies in a rock mass with a fracture network, thus giving insight into the triggering mechanism of large seismic events originating from a region distant from the production zone. Furthermore, this work sheds light on the development of a new methodology for the estimation of the risk of seismic events based on fracture distribution characteristics within a stiff rock mass.

1. Introduction

As mining depths have been increasing since the last century due to the depletion of shallow ore deposits, more challenging in-situ ground and stress conditions have been experienced in many deep underground mines. Such considerably adverse conditions are known to increase the risk of rockburst that involves the instantaneous release of strain energy as well as the ejection of rocks with high velocity from the surface of underground openings (Ortlepp, 2000). As such, rockburst can cause devastating damage to underground facilities and mining equipment, being a life-threatening phenomenon. It is hence indispensable to develop a methodology that enables a more accurate estimation of rockburst potential and its prediction.

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