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Estimating rock mass strength

Estimating rock mass strength (RMS) remains one of the challenges facing rock mechanics practitioners. The infinite variability of geology, weathering and alteration processes, the influence of mining and the inability to test rock mass strength directly, all pose great challenges to making reliable estimates. The experience of the practitioner, therefore, plays a crucial role in such estimates.

Although the problem with estimating RMS is not yet solved, in recent years another approach was developed that helps to provide more realistic estimates and generate and evaluate “what if” scenarios. This approach is called synthetic rock mass (SRM) and was pioneered by Itasca Consulting. It involves calibrating small-scale specimen strength, developing digitized detailed models of fracture and other defects called discrete fracture network (DFN) and estimating defect strength.

In close collaboration with Itasca, SRK used this approach on several world-class projects as input for further analysis, such as investigating block cave fragmentation. This approach is crucial, especially in rock masses that contain numerous defects such as microfractures, veinlets and cemented joints. It is encouraging to see that the results of SRM models are compatible with the empirical method of estimating rock block and rock mass strength developed by Dr Dennis Laubscher, author of one of the widely used rock mass classifications systems, in collaboration with SRK in 2000.

Practical experience gained from SRM analysis on mining operations and projects gives SRK a significant advantage in assessing rock mass strength more realistically than in the past using traditional industry tools.

Jarek Jakubec:

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