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| Ground fall in low-strength roof resulting from roof bolt failure |
Background
Analysis of MSHA statistics indicates that mines accounting for just 20% of underground coal production were responsible for 60% of all roof falls reported to MSHA between 1995 and 2003. These mines are located primarily in the Illinois and northern Appalachian coal basins. Reducing the number and rate of ground falls at these mines is a major concern for MSHA and for the mine operators.
Underground coal miners face two significant hazards associated with falls of ground: roof collapse and flying pieces of rock. Both types of hazards are more likely when roof strength (uniaxial compressive strength, or UCS) is less than 5,000 psi and the Coal Mine Roof Rating (CMRR) value is less than 40. Unfortunately, many of the ground control safety technologies developed for the broad range of U.S. mining conditions, such as CMRR and the Analysis of Roof Bolt Systems (ARBS), tend to be less useful when applied to mines with extremely weak roof.
This 4-year project will begin in FY 2006, with Peabody Energy, Black Beauty Coal, RAG Coal, and Anker Energy expressing interest in collaborating with NIOSH. The research will
- develop techniques for characterizing the strength and moisture sensitivity of weak roof,
- suggest guidelines for panel orientation, length, and duration while considering the time-dependent strength of the roof,
- develop methodologies for integrating supplemental and primary supports for maximum effectiveness, and
- enhance the use of roof screens through ergonomic evaluations, machine modifications, economic evaluations, and educational and information transfer programs.
Potential Outcome
The project will culminate in a comprehensive set of design technologies for operating in weak roof while addressing exploration, mine layout, roof support, and rock fall prevention. Project results will be transferred to the mining community in a series of open-industry briefings. Implementation of these design technologies should result in a 50% reduction in the number of roof falls at the target mines, which will in turn reduce the overall number of roof falls in the United States by 30%. The enhanced use of roof screening should reduce the number of rock fall injuries by 25% nationwide.