An integrated finite/discrete element method – discrete fracture network synthetic rock mass approach for the modelling of surface subsidence associated with panel cave mining at the Cadia East underground project

Abstract

The ability to predict surface subsidence associated with mass mining methods is important for both environmental impact and operational hazard assessments, however, the fundamental understanding of the complex rock mass response in block/panel cave mining settings remains limited. In this context, the use of numerical modelling provides an opportunity to investigate the factors governing caving mechanisms and to develop improved methodologies for the prediction of associated surface subsidence. In this paper the authors adopt an integrated numerical approach based on the analysis of the mechanical behaviour of discrete systems. This includes both more realistic representation of fracture systems and the modelling of rock mass behaviour as a combination of failure through intact rock material and displacement/rotation along predefined discontinuity planes. The focus of this paper is the numerical analysis of the factors controlling caving and associated subsidence, with emphasis on the potential impact of major geological structures and draw control. The numerical results clearly illustrate the importance of jointing and faulting conditions on subsidence development mechanisms and further emphasise the governing role of geological structure in defining the degree of surface subsidence asymmetry. The integrated modelling approach is shown to fully capture the complex rock mass response to caving associated with multi lift extraction and the modelled results are in agreement with analytical methods for simulation of gravity flow. It is argued that the predictive character of the integrated finite/discrete element method (FEM/DEM) - discrete fracture network (DFN) approach is beneficial in providing useful information particularly at the earlier stages of block/panel cave development. This allows the comparison of various mining scenarios, helping the mining engineers and mine management to select the best path forward.