3rd North American Rock Mechanics Symposium, Cancun, Mexico, 3–5 June 1998
Authors: R. R. Goodrich and J. F. T. Agapito (AAI), and C. Pollastro and L. LaFrentz (Energy West Mining Company)
Energy West Mining operates the Deer Creek coal mine in the Wasatch Plateau about 40 km (25 miles) southwest of Price, Utah, United States of America (USA). The mine extracts coal from the Blind Canyon Seam located within the Mesa Verde Group strata. A graben (Left Fork Graben) approximately 305.0 m (1000 ft) in width was encountered during development mining in the Rilda Canyon portion of the mine. Ground problems during gateroad development, including pillar-rib yielding and small bounces, occurred on the outside margins of the graben, but no abnormal mining difficulties were encountered inside the graben. Stress measurements were made using overcoring techniques along the 5th West gateroad at a depth of 579.5 m (1900 ft) to help evaluate stresses across the graben. While stress concentrations of nearly twice the magnitude of the expected in situ vertical stress were measured on the outside flanks of the graben, the measured vertical stresses within the graben were 17% less than anticipated. Stress analyses using the displacement discontinuity method were conducted for adjacent longwall panels to approximate the stress redistribution due to retreat of the longwall face through the boundary fault and into the graben. Results were calculated at multiple face positions and were compared to conditions experienced at other locations within the mine where longwall mining and stress analyses had been completed for an assessment of future minability and bounce potential.