Development of a semi-quantitative risk matrix for strain-burst hazard assessment – A numerical modelling approach in the absence of micro-seismic data

Abstract

Existing rockburst evaluation techniques are empirical in nature which limit their use to situations where seismic monitoring data is available. The proposed technique outlined herein is intended to be most useful to consider the risk of strain-burst events when seismic data is not available, e.g. during pre-feasibility or feasibility stage studies. As development progresses and seismic data is gathered, the proposed method provides an additional level of detail to confirm/inform the empirical seismic risk assessment techniques. Using the proposed numerical approach, the risk of strain-bursting can be considered for different excavation scenarios in order to choose an optimum solution prior to significant capital expenditure. This consideration of strain-burst events is implemented through a risk assessment matrix that has been developed based on the likelihood of the seismic mechanism manifesting as well as its potential consequence. Four indices have been defined that include 1) Pre-failure Damage Index ID, correlated to the hardening behaviour assessing the rate of damage within the rock mass prior to peak strength; 2) Energy Release Index IE, correlated to a brittleness index characterising in-situ conditions leading to failure; 3) Frequency Index IF, correlated to the size of damaged area indicating the potential re-occurrence of the event; and 4) Vulnerability Index IV, correlated to the damage size and location identifying vulnerability of the personnel exposed to the hazard. Each of these indices, when multiplied provides a risk ranking. A case study example is provided to demonstrate the determination of input parameters from a numerical model and the risk outcome. From the calculated risk, measures may be implemented and/or the effectiveness of alternative designs can be examined.