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Rock slope stability and design of granite lake open pit with the application of vacuum drainage : Gibraltar Mines Ltd., McCleese Lake, B.C.

University of British Columbia

Volume 1 of the thesis evaluates the rock slope stability of the South Wall of the Granite Lake open pit of Gibraltar Mines Ltd. Strength, structure and groundwater information was gathered which was comprised largely of 3.4 kilometers of line mapping data (3064 structures), previous reports and interpretation. The study indicated that deep-seated failures encompassing the entire pit wall were not probable. It was found that failures were restricted to bench (27 m) size, and consequently dictated a design whereby catchment berms of sufficient width were determined. This indicated an overall wall angle of 38° with isolated areas exhibiting steeper slopes. Steeper slopes would be possible under the following conditions : (a) Local drainage be applied (b) Control blasting be incorporated (c) A higher probability of ravelling be accepted. In addition Volume II of the thesis examines the benefits achieved by employing vacuum horizontal drainage. Horizontal drains were installed under vacuum in a mine slope. The benefit arises from an increased hydraulic gradient due to exhausting to a negative atmospheric pressure. The prototype was based on the well known civil engineering de-watering practice, well pointing. Results showed that a vacuum of 457 mm of mercury was obtainable in a fractured moderately permeable rock slope. Immediate drawdown of the water table occurred resulting in a total of 1.1 m of drop occurring after 59 minutes of operation. Flow increased from 0 1/s to 0.2 1/s discharging from the horizontal drains when the vacuum was applied. It was found that drawdown continued to occur with the water level dropping below the drain elevation. The system developed may be employed as a depressuri-zation tool for slope stabilization projects. The above was further reinforced through laboratory and numerical modelling.

Text

2010-04-13

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http://hdl.handle.net/2429/23411

Mining Engineering

University of British Columbia

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