Abstract

Mine development and operation in North and South America as well as Australia and Asia manage rockbursting conditions as a routine but always complex and difficult challenge. The hazard and the associated risks can be managed based on local experience, monitoring, informed data rich modelling and holistic understanding in a mature mining operation. In new mines, including large scale caving operations however, rockbursting poses a significant hazard to billions of dollars in initial infrastructure that must be designed and constructed prior to mining with minimal data and no local experience. In deep tunnelling around the world, a similarly blind approach (tunnelling into previously unexcavated ground) to hazard prediction and risk management must be taken.

Blind development for large infrastructure and mine access tunnelling is being carried out around the world at depths in excess of 2km. In complex tectonic regions, tunnels below 500m can experience rockbursting due to high horizontal stresses. In addition, while many of the empirical and semi-empirical tools for the prediction of burst prone ground are based on homogenous and massive rock conditions, tunnels in alpine areas and tunnels built for mine or mine panel access are, by nature, in highly heterogeneous and structured rock (joints, veins, fabric).

The author focusses in this paper on the prediction of brittle response potential to excavation under high stress and on the associated but separate potential for rockbursting within a tunnel or mine development heading. The rockburst mechanism considered here is tunnel generated dynamic rupture or strain bursting, distinct from remote or mine-generated events impacting the tunnel excavation. Consideration of rock petrology, fabric, and mechanical parameters allow an initial estimate of brittle response. The potential for energy storage and rapid release must be accounted for to understand the burst potential for as-designed tunnels.

1.
Introduction

Rockbursts are explosive failures of rock which occur when high stress concentrations are induced around underground openings (Hoek 2006) in brittle rock or rockmasses with brittle structure. In mining, there are many different mechanisms that lead to rockbursts. Pillar failure can be very violent if the pillar core reaches its capacity and the mine geometry is such that instantaneous deformations (system unloading) are large. Large stress changes associated with large scale mining can result in fault slip distant from the drift or shaft but capable of inducing sympathetic strain bursts (due to stress wave propagation) or seismically induced ground falls. In tunnelling, however, the most important mechanism is strain bursting of walls and the tunnel face, with or without structural control and as a result of the complex stress path within the near-field rock as the tunnel advances (Diederichs et al 2013).

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