Mitigation and Monitoring of Structural Distress in the Whitely Electrical Substation Due to Mine Subsidence

Underground coal mining is a common activity in the North East United States which often impacts surface facilities including electric transmission/substation systems. In long-wall mining, coal seams are excavated over large areas that cause near immediate, vertical and horizontal displacements of the ground surface above the mined seam. Structures located on these affected areas are subjected to varying permanent and temporary foundation displacements and rotations that may induce strains and stresses beyond the capacity of the structure. Cumberland Coal informed West Penn Power that long-wall mining would occur underneath the West Penn Power, 138kV, Whiteley Substation in early 2010. Their estimates indicated the ground would settle a total of approximately 4.5 feet. It was also necessary for West Penn Power to maintain service, from the substation during this subsidence event for its customers including the mining equipment. This paper discusses how the structural integrity of the substation components was maintained during the subsidence event by devising, implementing and monitoring various mitigation actions that reduced horizontal and vertical strains, compensated for the induced deformations in the structures, and reinforced components to tolerate anticipated deformations. Depending on the materials, geometry, and foundation layout of each structure, the impact of subsidence can be significantly alleviated by either stiffening of the panels and foundations to promote rigid body movements, and/or by softening the connections in order to facilitate limited mechanism types of movements. Whiteley substation functioned as needed during the subsidence event, as the result of these mitigation actions.