Study of Highway Subsidence Due to Longwall Mining Using Data Collected from I-79

摘要

Longwall mining is a common underground coal extraction technique in Appalachia. The extraction takes the form of panels whose width and length can reach approximately 1450 ft and 13000 ft; the coal seam thickness is roughly about 7.0 ft. Typical mine depth ranges from 640 ft to 830 ft. Longwall panels were mined underneath highway I-79 in the Cumberland and Emerald mines in southwestern Pennsylvania, causing large subsidence in the range of 4.5 ft to 5.5 ft that affected traffic safety and could have potentially damaged highway structures such as pavements, culverts, and bridge abutments. Mining under the highway prompted the close monitoring by the Pennsylvania Department of Transportation of the impact of mining on the highway sections above the mines. A substantial amount of data was collected that formed the basis of this work. The data included time series of surveying data and inclinometer data in selected points. With the aid of a genetic algorithm, a three dimensional subsidence model was developed. The model gives the spatial and temporal distribution of surface subsidence in terms of the depth of mining, the panel width, the thickness of extraction, and the location relative to the face of the panels. A FEM model was developed in order to better understand the mechanisms of subsidence. The results of both empirical and numerical modeling are presented.