Implementation of advanced constitutive models for the prediction of surface subsidence after underground mineral extraction

Surface subsidence is a typical problem for any underground mineral extraction. In order to choose an appropriate method of extraction, predict damage to infrastructure and other unwanted consequences of surface subsidence, it is necessary to model the surface settlement. Previous research has shown that the conventional constitutive models, which are built into commercial software, encounter considerable difficulties when attempting to predict subsidence troughs.

The troughs should be modelled deeper and narrower. To improve the predictions, the authors explore the possibilities of the implementation of advanced constitutive models by programming the Clay And Sand Model or CASM into the commercial finite-difference software FLAC3D by Itasca Consulting Group, Inc. CASM is a Critical State model that differs from the popular modified Cam-clay model, which is embedded within FLAC3D, by only two new parameters. Therefore, the implementation of CASM could be considered as a first step towards programming more advanced constitutive models in FLAC3D. After programming and validation of CASM, the model was used to simulate surface subsidence after a fictitious mine collapse. The simulations showed that CASM did not improve the prediction of the surface subsidence, and a different model may be more suitable.