Probabilistic assessment of long term surface subsidence due to room and pillar mining

The prediction of long term or residual subsidence due to room and pillar mining has been a challenge for engineers for some time. This issue becomes especially critical during urban development or construction of sensitive structures over abandoned room and pillar mines. Coal pillar strength and/or pillar dimensions diminish with time due to weathering, spalling and other factors resulting in a reduction of the pillar stability safety factor. A probabilistic method is proposed as a tool to determine the likelihood of failure of a coal pillar based on the upper and lower bounds of coal seam strength and pillar dimensions. Two case studies are presented as examples to estimate the likelihood of potential long term surface subsidence using this proposed probabilistic method including a proposed power plant over an abandoned mine and an existing impoundment and coal processing plant over another abandoned mine.