Managing rockbursting conditions in mine development and operational environments is a complex and difficult challenge. The hazard and the associated risks can be managed based on local experience, monitoring, and informed data-rich analysis. On the other hand, blind development for deep tunnelling is being carried out around the world at depths in excess of 2 km and rockbursting has become a common and serious challenge. The rockburst mechanism is predominantly tunnelling-induced dynamic rupture or strain bursting, distinct from remote or mine-generated events impacting mining excavations. Considerations of rock petrology, fabric, mechanical parameters and structure allow an estimate of brittle response. The potential for energy storage and rapid release must be accounted for to understand the burst potential early in the basic design stage for deep tunnels. Failure to do so can result in years of delay and unsafe conditions. In this paper a multistep semi-empirical approach for early strain-burst or dynamic rupture potential along deep tunnel alignments in variable ground is presented.

INTRODUCTION

Rockbursts are explosive failures of rock which occur when high stress concentrations are induced around underground openings (Hoek 2006) in brittle rock or rock masses with brittle structure. The Canadian Rockburst Handbook (Kaiser, McCreath, and Tannant, 1996) defines a rockburst as: ‘damage to an excavation that occurs in a sudden or violent manner and is associated with a seismic event’. Codelco (2008) uses the following definition of rockburst: ‘Loss of continuity of the production process of the mining operation, caused by the rupture and instant projection of the rock mass, associated with a seismic event.’ It is important to note the evolution, through these three definitions, from a term describing a mechanical phenomenon to a general and then a specific form of damage causing defined consequences. From a hazard and risk management perspective it is important to maintain a separation between the physical process of ‘dynamic rupture’ of the rock around a tunnel (the hazard) and the operational ‘rockburst’ impact (risk). The assessment of the hazard of dynamic rupture is the subject of this paper.

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