Abstract:

There are many challenges and pitfalls that exist for teaching and applying empirical design methods for underground rock mechanics. Some of the key components required for their successful use include:

Knowledge of the case history database that was used to create the empirical design method
Understanding the conditions that existed for the case histories
Understanding the failure mode and the key properties governing stability

This paper will discuss design techniques that govern rock mass behaviour, as opposed to intact rock failure or the failure of blocks or wedges. It should be recognized that these three failure modes can have completely different properties, even though a simple analysis of all three failure modes can be conducted with an estimate of the angle of friction and cohesion.

Unlike numerical or analytical design methods, there is no theoretical basis for the successful application of empirical design techniques. Literature and texts often poorly explain empirical design techniques, if they’re discussed at all. A student or practitioner must realize that observations, experience, and engineering judgement must be used when determining input values for empirical design methods.

Empirical design techniques are best used under the mining conditions that were present for the case histories used to develop the empirical design method. As blasting and stope backfilling methods evolve, the rock mass response to mining may change in ways the empirical design methods don’t consider. This doesn’t necessarily mean the design method is no longer useful, but new case histories may be needed to adjust the design method’s prediction of rock mass behaviour.

This presentation will review some well-known empirical design techniques for both tunnel and stope stability. Common errors, many of which have been made by the authors, will be discussed.

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Mr. Garrett Snell