Reinforcing Coal Mine Roof with Polyurethane Injection: 4 Case Studies |
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| Authors: | Gregory Molinda |
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| Institution: | (1) Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health (NIOSH), Cochrans Mill Road, P. O. Box 18070, Pittsburgh, PA, USA |
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| Abstract: | NIOSH has recently completed a study of the interaction between polyurethane (PUR) and coal mine roof in order to determine
the mechanism of reinforcement, in both highly fractured rock and unfractured rock. Four case studies of PUR reinforcement
are presented. At a West Virginia site, a borehole camera revealed the location of roof voids and guided the PUR injection.
By injecting polyurethane into a zone from 0.6 to 1.8 m (2–6 ft.) high in the roof, a roof beam was created and ongoing intersection
falls were halted. In another highly fractured roof in a western Pennsylvania mine, a total of 5.8 cm (2.3 in.) of rubbleized
rock was found in a zone up to 3 m (10 ft.) into the roof. Untargeted PUR injection filled approximately 1/2 of the fractures.
These two case studies showed that it is not necessary to fill up 100% of the void space to create stability. In the other
two field sites, polyurethane was injected into weak, but unfractured roof. Post-injection video monitoring showed that weak
bedding planes were hydraulically wedged open and polyurethane injected along bedding. The reinforcement value of this injection
method is limited because of the wafer-thin layer of PUR introduced along bedding, and the lack of a PUR “webbing” which would
serve as a structural framework to provide strength. It was determined that video inspection prior to PUR injection can aid
in identifying the fracture zones to target, and minimize “blind” pumping and loss of PUR. |
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| Keywords: | Coal mining Ground control Roof falls Roof support Polyurethane |
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