Techniques to Predict and Measure Subsidence and Its Impacts on the Groundwater Regime above Shallow Longwalls

This project investigated cracking associated with shallow longwalls using case studies from Beltana and Crinum Mines. The project trialed a number of techniques to measure the onset of subsidence and its impacts in terms of cracking.

The combination of tilt meters attached to data loggers and the influence function method for visualising subsidence offers a lower-cost way of monitoring subsidence. Resistance tomography and simple infiltration tests provide low cost ways of quantifying the impacts of cracking.

Available hydrogeological models for subsidence cracking have been reviewed and modified in the light of a geotechnical engineering assessment of the mechanics involved. This has led to a better appreciation of how the caving and fracturing zones develop and has identified where more research is required. A simple explanation for far-field valley closure in cases of sub-critical extraction has been developed.