PURPOSE:  Develop design guidelines for maximum roof spans and minimum pillar dimensions in underground stone mines. The effect of temperature and humidity on excavation stability will in addition be assessed and incorporated into the design guidelines.

RESEARCH SUMMARY:  Fall of ground accidents have been the largest single cause of fatalities in underground stone mines in the decade 1994 through 2003, while the fall of ground injury rates have remained essentially unchanged since 1995. The room-and-pillar method is used in all underground stone mines. The dimensions of the pillars and the roof spans in these mines are largely based on past experience without consideration of the local geotechnical parameters that affect stability. A result is that roof falls can occur unexpectedly and pillar dimensions can be inadequate to support the overburden. In addition, anecdotal evidence seems to indicate that fluctuations in mine air temperature and humidity affect the stability of the roof and ribs. This project has the objective to develop an engineered approach to stone mine layout design so that ground fall accidents can be reduced or eliminated.

The research will largely be based on the statistical valuation of the performance of existing underground stone mine layouts. Field data will be collected at more than forty operating mines representing a variety of geological and operating conditions. The field data will be supplemented by monitoring of roof and pillar behavior at selected sites. Laboratory testing of rock strength properties and numerical analysis of roof and pillar failure mechanics will be conducted to better understand the mechanisms of failure and stability. These studies will provide statistical as well as analytically based results that identify critical parameters affecting stone mine stability. The results of the studies will be used to develop a methodology for designing roof spans and pillar dimensions in underground stone mines.

The outcome of the project will be guidelines for improved techniques for underground stone mine design resulting in the reduction of potentially hazardous ground conditions and improved safety of mine workers.