Abstract:

Mining in the sill pillar regions in the 100/900 and 810 ore bodies has triggered significant seismic activity at Copper Cliff Mine. As such, several large magnitude events ranging from 2.5 Mn to 3.8 Mn occurred while mining in the sill pillar areas between September 2008 and April 2017. Following a 3.8 Mn event on September 11, 2008, Modified-cone bolts along with 0 gauge straps were first introduced as one of the tactical mitigation strategies to mine in highly stressed and/or burst-prone ground conditions at Copper Cliff Mine. With the advent of new dynamic ground support elements such as D-bolts/Par 1, Yield-loc and MD-bolts, it provided us an opportunity to pick and choose the suitable dynamic support elements for varied rock mass conditions.

This paper reviews the evolution of the dynamic support system, the design rationale, and how newly introduced ground support elements lead to modifications of the dynamic ground support standards at Copper Cliff Mine. This paper also presents case studies for each dynamic support element, such as Modified-cone bolts, D-bolts and MD-bolts along with #4-gauge screen, 0-gauge screen and FS-46 split sets. Each case study will provide an overview of how different dynamic support systems performed during large magnitude seismic events and how modified dynamic support system helped to significantly reduce/minimize damage to mine openings and/or the installed ground support system. It also gives an overview of lessons learnt and how such experiences paved the way to employ other tactical measures, such as large-scale sill pillar de-stress blasts, to alleviate the risk of causing potential damage from large magnitude seismic events. Geotechnical instrumentation has also been used to monitor the induced stress change to identify the high-risk zones and evaluate additional support requirements.

Biography of the presenter: Reddy started his career as Junior Mine Engineer (Trainee) in India with Western Coal Fields Ltd in 1992 and later worked at National Institute of Rock Mechanics (NIRM), Kolar Gold Fields (India) during 1995 - 2001. Mr. Reddy moved to Canada in September 2001 to pursue M.A.Sc in Rock Mechanics at Laurentian University. Mr. Reddy joined Vale, Sudbury Operations in early 2007 and is currently working as Chief Ground Control Engineer at Creighton Mine. In his current role, Mr. Reddy is responsible to oversee the ground control programs at Creighton Mine as well as Copper Cliff North and South sides. His responsibilities include: optimal design of stope/excavation sizes, mining methods/sequence, ground support systems (static and dynamic), major sill pillar destress strategies, seismic systems and other geotechnical instrumentation to monitor the rock mass response to mining including effectiveness of major destress blasts in high stress ground conditions.

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Andrew Breckon