Diccionario Tecnico

Empirical approaches for opening design in weak rock masses
Tom Brady, Lewis Martin and Rimas Pakalnis

A major focus of ground control research presently being conducted by the Spokane Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH) is to incorporate weak rock masses (such as are associated with operations in the Carlin Trend in Nevada) into existingdesign relationships. The original database that led to most of the empirical design relationships presently employed in hard-rock mining was derived from fair-to-good-quality rock. In this study, the relationship between weak rock quality and opening design (non-entry/entry methods) is being investigated. The common factor in all mines is a weak back or wall. This work attempts to provide toolsthat will enable a mine operator to make economic decisions that will also ensure a safe working environment.
Tom Brady (for correspondence – E-mail: thb6@cdc.gov)and Lewis Martin are at the Spokane Research Laboratory, National Institute for Occupational Safety and Health, 315 East Montgomery Avenue, Spokane, WA 99207-2291, USA (E-mail: ljm8@cdc.gov); Rimas Pakalnis is at the Mining Department,University of British Columbia, Vancouver, British Columbia, Canada (E-mail: rcp@mining.ubc.ca). © 2005 Institute of Materials, Minerals and Mining and Australasian Institute of Mining and Metallurgy. Published by Maney on behalf of the Institutes. Manuscript accepted in final form 24 February 2005. Keywords: Weak rock masses, empirical design, opening design

Table 1

Ground control injuriesand fatalities in underground ground gold mines in Nevada, 1985–2000
7 4 49 46 110 216 69

Fatalities Permanent disabilities Lost-time injuries Restricted-activity injuries Other injuries Total Reported rock falls with no injuries*

*Includes MSHA data for non-injury incidents where a reportable fall of ground occurred but did not cause injuries because the mining area was unoccupied.underground mining is often difficult and hazardous, as indicated by the number of injuries and fatalities from uncontrolled falls of ground (Table 1). A comparative analysis by the Mine Safety and Health Administration (MSHA)9 for the years 1990–1999 indicated that the number of roof-fall injuries in Nevada has varied from a low of 8 in 1991 to a high of 28 in 1995 and 1997. As late as 1999, the numberof injuries was still in double figures (Fig. 1). Analysis of the MSHA data shows 76·7% of the roof falls were from the back, 18·6% were rock falls from face or ribs with the remaining 4·7% of an unknown nature. The mines are required to report all injuries to MSHA by law. Mining is a dynamic process, and ground conditions can change over a short distance. A mine opening must perform in apredictable manner over its expected life.

INTRODUCTION
Researchers at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health, Spokane, Washington, USA, and the University of British Columbia, Vancouver, Canada, have assembled a team to develop underground design guidelines for safe and cost-effective mining within a weak rock mass. Such work also includesdeveloping novel support methods, such as the use of synthetic fibre reinforced shotcrete, ways to undermine underhand-and-fill backfilled stopes, and assess supports presently in place in weak rock masses. In the present study, rock mass interaction with grouted bolt supports was investigated in three mines in Nevada and backfill, pillar, and bolt support were studied in one. Many Nevada gold depositsare found in intensely fractured, faulted, and argillised host rock. As a result,
DOI 10.1179/037178405X44494

1

Injuries in Nevada, 1990–2004

Mining Technology (Trans. Inst. Min. Metall. A) March 2005 Vol. 114 A13

Brady, Martin, Pakalnis Empirical approaches for opening design in weak rock masses

Table 2 Nevada mines database: back spans in weak rock
RMR (%) Mine 1 45 45 40...