Gale described developments in using the approach at the recent subsidence management conference organised by The Mine Subsidence Technological Society (MSTS).
The two-dimensional model was developed for longwall caving but was applicable to model ground subsidence, overburden damage and induced hydraulic conductivity, or water flow, Gale said. Though further research and verification needs to be completed yet.
Hydraulic conductivity, or water flow, can be estimated using the modeling method. This allows a picture to be built of the impact on aquifers and water bodies. The approach aims to provide a better understanding of the fracture distributions and their impact on conductivity.
Stress distribution around longwall panels, caving and subsidence create a fracture network of bedding, shear and tension fracture planes. This fracture network can extend outside the mined panel. For instance near surface bedding planes can be mobilized as a result of large scale stress redistributions rather than induced subsidence.
Modelling can be used to provide additional information about the fracture networks around panels. This can be fed into the mine plan to evaluate the effect on aquifers and surface features.
“Modelling is viewed as a powerful tool to be used in conjunction with other approaches,” Gale said, “however ongoing monitoring and validation is an essential part of the process to ensure the ground behaviour is being simulated in a realistic manner.”
Where the approach has been applied to sites, the modeled behaviour is consistent with the monitored behaviour of aquifers and inflows.
Gale said the modeling has been shown to provide a good understanding of fracture networks created and an estimation of the conductivitiy within the overburden.
Current ACARP research has involved modeling water flow at a super critical shallow operation in the Bowen Basin and a deep single, sub critical panel in the Bulli Seam. Research is continuing to investigate ways to calculate permeability better.
