PURPOSE:  Reduce groundfall injuries in Nevada underground mines excavated in weak rock masses. Develop new mining techniques using proven mine design techniques and adapting them to underground mines in weak rock.

RESEARCH SUMMARY:  Underground mining is one of the most hazardous occupations worldwide. Most of the fatalities associated with underground mining are attributed to either groundfall or haulage. In the United States during the 1990’s, injuries and fatalities from falls of ground were an order of magnitude higher in mines excavated in weak rock masses than in underground mines in stronger rock (Mine Safety and Health Administration at www.MSHA.gov).

To address the controlling and confounding factors involved in determining risk exposure in underground mines in weak rock masses, a twofold research approach was adopted. The first was to collect data to establish mine design criteria (rock mass ratings, span widths, and estimated loss of slough). The second was to study the use of fibre-reinforced shotcrete as a type of ground support. By conducting rigorous field tests and analyzing the data from the fiber-reinforced shotcrete used as immediate support at the Rodeo Mine, NIOSH personnel were able to provide information on new underground support design criteria that will lead to a safer working environment for underground miners.

Nevada Gold Book. An underground mine design manual for weak rock mass conditions in hard-rock mines has been developed. It contains information that relates span curves, rock mass rating (RMR) values, stope design curves, and ELOS values. This manual has been adopted at most mines in Nevada, Idaho, Montana, and Colorado.

Shotcrete. NIOSH and the Barrick Gold Mining Company collaborated at Barrick's Rodeo/Meikle gold mines in Nevada to evaluate and compare the use of fibre-reinforced shotcrete to the use of steel screens with shotcrete. A field test of the two methods was conducted in a production test drift from May to October 2002. Analysis of test results by both Barrick and NIOSH SRL personnel confirmed a statistically significant improvement in ground control when fibre-reinforced shotcrete was used. Subsequently, Barrick decided to utilize fibre-reinforced shotcrete for 30% of its underground shotcrete applications.

Shotcrete Field Test. An Australian round panel test system was designed, built, and tested during FY04. This system gives mines the ability to test the strength of shotcrete in situ for immediate design and engineering parameters. Several mines have utilized these tests to improve underground support.