STABILITY PREDICTION AND PERFORMANCE OF HIGHWALL STEEPENING IN WEAK ROCK

摘要

The Montana Tunnels Mine was mined out to arndepth of 900 feet at the end of 1999. The first signsrnof instability were recognized in 1996 along thernupper slope area of the northwest sector when thernpit was mined out to a depth of approximately 500rnfeet. To extend the life of mining operations, it hasrnbeen proposed to extend and steepen the northwestrnhighwall to a depth of 1000 feet. Slope stabilityrnanalyses were carried out using the UDEC softwarernprogram to assess the stability and deformation ofrnthe proposed highwall design. Back analysis of anrninstability in 1997 along the upper slope section andrnhighwall deformation to date has indicatedrnreasonable agreement with the observed mode ofrnfailure and displacement monitoring results. Thernresults of detailed analyses of the proposed highwallrndesign have indicated very limited additionalrndeformation, further development of tension cracksrnis unlikely and large-scale instability is not expectedrnto occur. A total of 40% of additional mining hasrnbeen completed and ongoing displacementrnmonitoring to date has confirmed very limitedrnadditional movement and no further tension crackrndevelopment.