Rock mass characterisation and stope design

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The majority of the underground mining in Canada uses a method of extracting the ore called open stoping.  A stope is a large underground excavation where the ore has been blasted and removed and these opening can often be the size of a ten story apartment building.  The hanging wall and footwall of these openings follow the contact between the ore and the waste.  Waste rock failing or sloughing off these walls during mining mixes with the ore and dilutes the grade.  This sloughing of waste rock is called stope dilution and can create significant additional expense for mines since this material has to be hauled to surface, crushed and milled with the ore.Reducing stope dilution is major goal for many underground mining operations.  One of the main factors governing hanging wall dilution is the strength of the rock mass.  The goal of this research is to improve the measurement and application of rock mass properties for stope design.  In the process of reaching this goal, methods of predicting hanging wall stability and dilution will be improved through better data collection, interpretation and analysis.  The current approach for assessing rock mass properties results in a single rock classification number.  The approach for determining this value is relatively insensitive to improved, more accurate methods of measuring the rock mass properties.  The methods used to link the various rock mass properties to obtain a single number have been fixed since the early 1970s, based on observations made primarily in civil engineering tunnel work.  Stope survey data present an untapped source of information linking opening geometry and rock mass properties to rock stability, measured as a depth of failure or hanging wall dilution.  This research will improve methods of quantifying rock mass properties as well as assist operating Canadian mines save money through reduced stope dilution.