Spatial trends in rock strength: can they be determined from coreholes?
Mark-C; McWilliams-LJ; Pappas-DM; Rusnak-JA
Proceedings of the 23rd International Conference on Ground Control in Mining, August 3-5, 2004, Morgantown, West Virginia. Peng SS, Mark C, Finfinger GL, Tadolini SC, Heasley KA, Khair AW, eds., Morgantown, WV: West Virginia University, 2004 Aug; :177-182
Mine planning for a new reserve is based on information obtained from exploratory coreholes. A critical component of an exploration program is the geotechnical evaluation. Poor assumptions about roof conditions greatly add to the risks of mining. Rock mechanics testing is central to a geotechnical exploration program. Typically, three to five uniaxial compressive strength (UCS) tests are made to characterize a particular roof unit at a given corehole. The average (mean) of these tests is taken as the UCS for that location. Isopach contour maps are then used to show spatial trends in roof strength. Two issues are raised by this traditional approach. The first is due to the large variability in UCS values that is typical even within a single unit from a single hole. The average UCS might be higher at corehole A than corehole B, but the difference may not be statistically significant. The second issue is whether widely spaced coreholes can identify valid spatial trends in rock strength. The answer depends on whether rock strength changes over distances that are longer or shorter than the corehole spacing. This is a classical geostatistical problem. Although geostatistics have been used to investigate many coal quality parameters, they have seldom been used to evaluate rock strength. This paper describes an extensive investigation of these issues conducted by NIOSH in collaboration with Peabody Energy. The study used the Peabody Rock Mechanics Database, which contains more than 10,000 individual test results. Data from four important roof units were subjected to statistical analysis: (1) Brereton Limestone above the Herrin No. 6 Seam (Illinois), (2) Turner Mine Shale above the No. 9 Seam (Kentucky), (3) sandstone above the Eagle Coal (West Virginia), and (4) shale above the Eagle Coal (West Virginia). The study did not find significant spatial trends in rock strength in any of the cases. Perhaps there are none, or perhaps the exploratory coreholes were just too far apart to see them. These results have valuable implications for the design of geotechnical exploration programs.
Ground-control; Safety-research; Underground-mining; Coal-mining; Rock-mechanics; Geostatistics
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
Peng-SS; Mark-C; Finfinger-GL; Tadolini-SC; Heasley-KA; Khair-AW
Research Tools and Approaches: Control Technology and Personal Protective Equipment
Proceedings of the 23rd International Conference on Ground Control in Mining, August 3-5, 2004, Morgantown, West Virginia