Assessment of sequenced room and pillar retreat coal mine subsidence using the Surface Deformation Prediction System (SDPS)

Due to the slower pace, and often irregular pattern, of retreat mining, ground deformation effects can be more challenging to predict as compared to longwall coal mine subsidence. Retreat mining results in a mining section that varies by the pillar length being mined, which often results in a surface expression of the interface of the mined area with remaining pillars along the same pillar line. The resultant surface expression is an L-shaped corner that can cause momentary surface deformation movements in the axis parallel to the retreating pillar line. This results in a retreat mining subsidence “wave” that has the potential to cause surface movements both perpendicular and parallel to the retreating pillar line. The surface movement resulting from retreat mining can increase the potential for damage to surface structures. The Surface Deformation Prediction System (SDPS) is used to model the deformation expected from retreat coal mining. SDPS predictions result in the ability to plot ground deformation development curves for numerous indices, allowing for assessment of various damage thresholds as retreat mining approaches, passes beneath, and moves away from structures. The predictions do not incorporate a time factor; therefore, the results at each step correspond to a final static movement.