Mining Publication: Reinforcing Coal Mine Roof with Polyurethane Injection: 4 Case Studies
Original creation date: October 2008
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.
Authors: GM Molinda
Peer Reviewed Journal Article - October 2008
NIOSHTIC2 Number: 20034612
Geotech Geol Eng 2008 Oct; 26(5):553-566
See Also
- ARBS - Analysis of Roof Bolt Systems - 2.5.02
- Development and Application of the Coal Mine Roof Rating (CMRR)
- Diagnosing and Controlling Moisture-Sensitive Roof in Coal Mines
- Effects of Stimulation Treatments on Coalbeds and Surrounding Strata: Evidence from Underground Observations
- Geologic Hazards and Roof Stability in Coal Mines
- The Introduction of Roof Bolting to U.S. Underground Coal Mines (1948-1960): A Cautionary Tale
- Numerical Modeling for Increased Understanding of the Behavior and Performance of Coal Mine Stoppings
- Performance Characteristics for Welded Wire Screen Used for Surface Control in Underground Coal Mines
- Roof Span Design for Underground Stone Mines
- A Spatial/Spectral Domain Microwave Coal Seam Imaging Sensor-Progress in Signal Processing
- Content source: National Institute for Occupational Safety and Health, Mining Program