Geotechnical factors influencing a time-dependent deformation mechanism around an entry in a dipping seam
- Department of Energy, Spokane, WA (United States)
- Maleki Technologies, Inc., Spokane, WA (United States)
The U.S. Bureau of Mines and Cyprus Shoshone Coal Corp. conducted a study of deformation mechanisms in strata around a longwall gate road system at two sites in an underground coal mine near Hanna, WY. Of particular interest was time-dependent (on the order of several months) roof deformation. Strata above and below the coal seam are very weak, carbonaceous mudstones that have cohesionless planes of weakness oriented along bedding, which dips approximately 8{degrees} to 16{degrees} at N 49{degrees} E. An extensive array of instrumented roof bolts, roof extensometers, and biaxial stressmeters were installed during development mining at these two sites under variable depth of cover [183 to 335 in (600 to 1,100 ft)], seam dip (10{degrees} to 16{degrees}), and top coal thickness [estimated to be 0.30 to 0.61 in (1 to 2 ft) on the downdip side of the entry]. Bolt load and roof deformation histories during the entry development periods were compared. Bolt loads at site 2 were less than those at site 1, which is consistent with the amount of overburden. Deformation magnitudes at site 2 were similar to those at site 1, but deformation rates were approximately 44% greater and nearly constant over time, whereas the deformation rates at site 1 decreased exponentially over time. Also, most deformation occurred above the bolt horizon at site two, but extensometer measurements at site 1 showed that a significant amount of deformation occurred within the bolt horizon. The most significant factor that influenced bolt tension and time-dependent strata deformation was strength and Young`s modulus of the strata. Finite-difference models support this conclusion.
- OSTI ID:
- 405610
- Report Number(s):
- CONF-9608121-; TRN: 96:005886-0052
- Resource Relation:
- Conference: 15. International conference on ground control in mining, Golden, CO (United States), 13-15 Aug 1996; Other Information: PBD: 1996; Related Information: Is Part Of Proceedings of the 15th international conference on ground control in mining; Ozdemir, L.; Hanna, K.; Haramy, K.Y. [eds.] [and others]; PB: 783 p.
- Country of Publication:
- United States
- Language:
- English
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