Calibrated parameters for the prediction of subsidence at Mandalong Mine

The consent conditions at Mandalong Mine require that subsidence deformations must not change the flood hazard category or subject a dwelling to deformation beyond safe surface and repairable (SSR) unless permission is granted by the effected landholder. The subsidence prediction in 2003 utilised an analysis of sag based on voussoir beams and of pillar compression based on foundation engineering principles. The model uncertainty for the sag analysis was assessed to be relatively high with a low parameter uncertainty, while for the pillar compression the model uncertainty was low but the parameter uncertainty was high. Up to June 2009, seven longwalls have been extracted. The consent conditions have not been breached. Both the voussoir beam and pillar compression models have been demonstrated to be valid. There have been changes in the way in which key input parameters are estimated.