Coal extraction and ground movement at Huntly East Coal Mine, New Zealand

This paper provides a novel and representative method for characterising coal extraction layouts. This method was used to support an investigation of the correlation between the extraction layout and the ground movement in Huntly East coal mine, New Zealand. A 250 m borehole inclinometer was installed to monitor the strata movement that occurred as underground mining approached the borehole, by measuring the movement of the casing within the borehole. The inclinometer measurement was undertaken once a month on average. In order to analyse the correlation between coal extraction and ground movement, multiple extraction areas for each month were organised into one area. In order to determine the magnitude and location of the extraction in terms of its induced ground movement, the delay time of subsidence was first defined by data analysis. The correlation between the coal extraction and the ground subsidence had been established. Finally, the correlations between the nearest extraction edge and the lateral movement were represented by three nonlinear regression equations. The three equations have been validated by numerical modelling; this is not discussed in the paper. Lateral movement has been analysed and characterised in this study, but vertical subsidence has only been identified to exist and was not discussed in detail due to the limited dataset available.