Mine to tunnel scale discontinuum simulation of repeated dynamic loading of mine excavations
David Gilbert and Kevin Stacey
Compañía Minera Antamina S.A. Peru
Underground excavations are subjected to complex stress changes caused by nearby mining, but may also be affected by repeated dynamic loading from blasting and seismic events. In some cases, the combined, cumulative effects can lead to unforeseen damage, displacement and instability.
Simulating dynamic loading of an underground excavation is a very complex task. The state of rock mass stress, damage and deformation must first be simulated sufficiently requiring small scale structures to be explicitly modelled. Supporting elements must be represented with high similitude and then the dynamic event must be applied to the system in the case of blasts, or evolve as a consequence of rock mass instability for seismic events. A special case is for the effect of pit blasting on underground excavations – discontinuous rock phenomena at scales from mine, to bench, to pillar, to tunnel need to be captured and this represents one of the most computationally intensive tasks in mine simulation.
Recent advances in computer power allow these tasks to be completed at a mine scale, incorporating discontinuities and geological detail matching the best practice for static Finite Element analyses. The results are a worthwhile contribution to mine decision making, but require careful interpretation and thoughtful inputs – even more so than quasi-static analysis – as the cumulative effects of unfavourable modeling practices are greater.
Some learnings from experiences with mine scale, discontinuum dynamic simulation are summarised, including a discussion of considerations of scale and similitude for this type of analysis.