Predicting the Height of Longwall Mining Induced Connective Fracturing and Permeability Enhancement

Longwall mining causes the strata overlying the coal seam to fracture, break and collapse into the void space resulting from the coals extraction. Estimating the height of longwall mining induced strata fracturing, fracture connectivity and the height of complete groundwater drainage is a contentious issue and there seems to be some misconception and misunderstanding among the practicing engineers and groundwater modelers. This knowledge gap has put extra demand for rigorous study and the development of more sophisticated and reliable assessment tools. The extent of mining induced subsurface deformation, fracturing, surface subsidence, and aquifer interference is largely controlled by local lithological conditions, mining methods and mine layouts. Thus it is imperative to develop methods/tools that, unlike empirically based strata desaturation height estimation methods, can properly consider all factors and accurately predict strata deformation and subsequent fracturing (particularly connective fracturing) in varied hydrogeologic environment to assess the impact of mining on groundwater. This paper describes the use of monitoring data from a mine site in Queensland and a Distinct Element model to assess strata fracturing during longwall extractions.