ABSTRACT: A novel approach of ameliorating the seismic risk to off-reef infrastructure was developed for a relatively deep level gold mine. Mining is being carried out in an extensively geologically disturbed environment, which has resulted in numerous damaging seismic events historically. The stability of off-reef excavations was threatened under further mining, and the long term viability of the mining operation had to be assessed. A seismic hazard assessment methodology using numerical modelling, both static and dynamic, and seismic back-analysis was developed. This methodology went beyond quantifying the probability and potential magnitude of large scale seismic failure, and estimated in addition potential levels of peak ground motion at critical locations. The estimates of potential peak ground motion under the planned mining were then turned into actionable knowledge, namely: “Mining strategies formulated to minimise the seismic hazard associated with future mining (prevention)”; and “Strategies formulated to minimise the risks to people and property in the light of remaining hazards (protection)”.
Rockfall and rockburst hazards in the AngloGold Ashanti underground operations are managed using the AngloGold Ashanti Fall of Ground Management (FOGM) system (Laas 2003) which deals with both rockfalls and rockbursts. One aspect of this system was to address a particular problem, namely the seismic hazard and risk to off reef infrastructure in the medium depth scattered mining environment (see description of mining method in section 1.2). The first step was to back analyse historically large seismic events with respect to the existing mining configuration and the geometry of the known seismogenic geological structures. Seismic events were obtained from a comprehensive seismic catalogue, and a numerical modelling package (Map3D) based on the three-dimensional boundary element formulation was used to estimate static stress and deformations along the geological structures.