Underground » Environment - Subsidence and Mine Water
A detailed review of available mine subsidence data collected over longwall panels within the Newcastle Coalfield and an empirical subsidence prediction methodology has been developed by Strata Engineering (Australia) Pty Ltd.
The subsidence review included the collation of previously published data by mining company personnel and data obtained directly from the mines. In all, data for over 50 longwall panels and 200 boreholes has been included in the model and represents the full range of overburden conditions expected in the majority of the remaining reserves of the Newcastle Coalfield. The model represents an extensive upgrade of the subsidence prediction methodologies published by the NSW Inspectorate in 1987.
A significant effort has been invested in the validation of the resultant model with 90 to 95% of the subsidence measurements (including the Subsidence Reduction Potential of massive overburden lithology) above single and multiple longwall panels in the database can be repredicted successfully within 95% confidence limit boundaries determined for the model.
Although the subsidence profile prediction work was not originally included in the project brief, the ability to generate predicted subsidence profiles for comparison with measured profiles provided a powerful validation tool for the overall model development.
The most obvious benefit to the industry with regard to the work presented is that a simple (but robust) empirically based tool is now available to allow improved 'greenfield' and 'brownfield' subsidence management planning to be integrated with overall mine planning; the impact of proposed longwall panel and chain pillar dimensions can be assessed quickly using the model. Implementation of subsidence damage risk action plans will also be easier to manage once actual subsidence measurements are available.
As the model can provide upper and lower limits for a proposed series of longwall panels, the "geological anomaly" term that has been frequently used in the past to explain significant differences between predicted and measured subsidence is now likely to be reduced. This of course will be a great benefit to all stake-holders.
The conceptual methodologies and techniques developed during this project are considered to be generic enough to be applied successfully in other coalfields, once a similar review of available data is completed.