Mining Publication: Design of Primary Roof Support Systems in U.S. Coal Mines Based on the Analysis of Roof Fall Rates

Each year, about 2,000 falls of supported roof occur in the more than 800 underground U.S. coal mines. Therefore, to help improve the design of primary support systems, the National Institute for Occupational Safety and Health (NIOSH) conducted a nationwide study of roof falls in over 2,500 km of roadways at 37 coal mines. Information on the roof falls as well as other geotechnical, mining, geologic and roof bolting factors were collected and quantified. Then a multi variate statistical analysis was conducted on the data with the roof fall rate being the outcome variable. The results were used to derive preliminary design guidelines for predicting the roof bolt length, capacity, and pattern required to effectively reduce the roof fall rate. The equations are fairly limited by a relatively high statistical variance in the data. Also reported is a recent survey of U.S. roof bolt manufacturers that shows a significant change in bolt types used over the last ten years.