Development of design criteria for working under weak rock masses

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This is an extension of research performed by the author over the past fifteen(15) years in developing design tools for the operator. Empirical design approaches have been developed by the candidate's group that are employed in mine designs throughout the world. These have been developed largely for rock masses classified as being fair to good. The mining industry is now extracting ores that require mining under more difficult conditions such as under weaker rock masses. The original "Span Design Curve" as developed for man-entry methods  identifies the critical span that can be open for a given rock mass. It is largely based upon rock masses having an RMR in excess of 55% or Q greater than 4.0 that are largely unsupported. This proposal looks at extending the database to incorporate the weak rock masses along with quantifying the effect of support on the overall design process. The objective is to develop a safe engineered work environment as mining occurs immediately underneath the exposed back and causes the greatest exposure to the operator. An expanded database will be compiled with particular emphasis on Canadian conditions and practices. Individual mine openings will be analysed in terms of stress, structure and the rock mass in order to assess back stability and to develop criteria for the engineer to ensure a safe workplace. The failure mechanism will be modeled and calibrated to actual mine observed conditions for variable rock masses. This will estimate the depth of failure and consequently the potential loading that may act on the support. This will result in design curves for varying support categories. Tools such as analytical, empirical and numerical codes will be calibrated to site observations and measurements to arrive at a workable solution for purposes of design of backs within weak rock masses for a given support type.