Abstract
The response of the ground surface above longwall panels in a virgin geologic environment can only be approximated by prediction models developed from subsidence measurements made in other coal mining districts. Above the 10-ft thick seam longwall at the York Canyon Mine, west of Raton, New Mexico, the measured angle of draw for super-critical panel 4N was from 5° to 15° which is 0.09 to 0.27 times the depth, outside the panel. This compares to the British National Coal Board (NCB, 1975) predicted angle of draw of 35°, 0.7 times the depth. The measured subsidence effects outside panel 4N did not extend even one-half as far as the NCB predictions. However, measured subsidence at York Canyon persisted to about 0.85 times the depth behind the face and above the cave which closely compares with the NCB prediction of 0.9 times the depth. Measured maximum York Canyon horizontal strains are 21,000 u-in./in. tensile and 22,000 u-in./in. compressive whereas, the NCB would predict 13,600 u-in./in. tensile and 10,700 u-in./in. compressive. Surface response ceased almost as soon as mining stopped, which parallels the NCB surface response prediction.
The mountainous terrain above panel 4N complicated the surface response because of the lateral component of the downslope movement. Permanent lateral displacements resulted in movement toward the draws crossing the panel and away from the ridges. The same effect reduced vertical subsidence at the draws and increased vertical subsidence at ridgelines.
