Canyon Fuel Company
Longwall Mining—Shield Support Densities
AAI has performed a full range of geotechnical analyses for SUFCO in support of their longwall operations, including pillar design, longwall shield support evaluations, and subsidence analyses. SUFCO currently mines with two-legged 970-T Joy shields in the Pines Tract (Upper Hiawatha Seam) under nominally 1,000 ft of cover. Three primary differences exist in the future tract: (1) deeper cover up to 1,900 ft, (2) a lower average face height on the order of 8.5 to 9 ft in some parts of the tract compared to about 10 to 11 ft in the Pines Tract, and (3) different roof lithology. The general lithologic differences in the immediate roof are (1) a thinning and disappearance of the Yellow Parting, (2) emergence of a relatively thick Orange Parting (several feet thick), and (3) an overall increase in strength and stiffness, based on laboratory core testing. Empirical analysis and numerical modeling was applied in this study to evaluate the implication of these factors for support density. The analytical methodology is consistent with that of a parallel support density study conducted for Arch Bituminous Western Group’s Mountain Coal West Elk Mine in March 2005.
Proposed options for longwall mining in the Pines Federal Coal Lease Tract were evaluated for subsidence-related impacts to cultural resources, escarpments, perennial streams, and ponds as part of the mine plan Environmental Impact Statement study. Predictions of surface ground strain, displacement, and stream gradient changes were developed using AAI’s proprietary influence function computer code BASIN. Models were calibrated to existing subsidence on the property. AAI provided permitting support with the USFS and the BLM. Permitting was successful and monitored subsidence in the tract agreed closely with engineering predictions.
For additional information on the SUFCO Mine, please read the following technical paper: Subsidence Behavior at the SUFCO Coal Mine, Utah