science

Mining rock mass rating

Mining rock mass rating is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mining rock mass rating rather than just read about it. In short: The Mining Rock Mass Rating (MRMR) is a geomechanics classification system for rocks, within geotechnical engineering. DH Laubscher developed the Mining Rock Mass Rating system by modifying the Rock Mass Rating (RMR) system of Z.

Key takeaways

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Reference excerpt

The Mining Rock Mass Rating (MRMR) is a geomechanics classification system for rocks, within geotechnical engineering. DH Laubscher developed the Mining Rock Mass Rating system by modifying the Rock Mass Rating (RMR) system of Z. T. Bieniawski. In the MRMR system the stability and support are determined with the following equations:

RMR = IRS + RQD + spacing + condition in which: RMR = Laubschers Rock Mass Rating IRS = Intact Rock Strength RQD = Rock Quality Designation spacing = expression for the spacing of discontinuities condition = condition of discontinuities (parameter also dependent on groundwater presence, pressure, or quantity of groundwater inflow in the underground excavation) MRMR = RMR * adjustment factors in which: adjustment factors = factors to compensate for: the method of excavation, orientation of discontinuities and excavation, induced stresses, and future weathering The parameters to calculate the RMR value are similar to those used in the RMR system of Bieniawski. This may be confusing, as some of the parameters in the MRMR system are modified, such as the condition parameter that includes groundwater presence and pressure in the MRMR system whereas groundwater is a separate parameter in the RMR system of Bieniawski. The number of classes for the parameters and the detail of the description of the parameters are also more extensive than in the RMR system of Bieniawski. The adjustment factors depend on future (susceptibility to) weathering, stress environment, orientation, The combination of values of RMR and MRMR determines the so-called reinforcement potential. A rock mass with a high RMR before the adjustment factors are applied has a high reinforcement potential, and can be reinforced by, for example, rock bolts, whatever the MRMR value might be after excavation. Contrariwise, rock bolts are not a suitable reinforcement for a rock mass with a low RMR (i.e. has a low reinforcement potential). Laubscher uses a graph for the spacing parameter. The parameter is dependent on a maximum of three discontinuity sets that determine the size and the form of the rock blocks. The condition parameter is determined by the discontinuity set with the most adverse influence on the stability. The concept of adjustment factors for the rock mass before and after excavation is very attractive. This allows for compensation of local variations, which may be present at the location of the rock mass observed, but might not be present at the location of the proposed excavation or vice versa. In addition, this allows for quantification of the influence of excavation and excavation induced stresses, excavation methods, and the influence of past and future weathering of the rock mass.

See also Core recovery parameters Geotechnical engineering Hoek-Brown failure criterion Rock mass classification

References

Further reading Bieniawski, Z.T. (1989). Engineering Rock Mass Classifications. Wiley-Interscience. p. 272. ISBN 978-0-471-60172-2. Hack, H.R.G.K. (25–28 November 2002). "An evaluation of slope stability classification. Keynote Lecture.". In Dinis da Gama, C.; Ribeira e Sousa, L. (eds.). Proc. ISRM EUROCK’2002. Funchal, Madeira, Portugal: Sociedade Portuguesa de Geotecnia, Lisboa, Portugal. pp. 3–32. ISBN 972-98781-2-9. Pantelidis, L. (2009). "Rock slope stability assessment through rock mass classification systems". International Journal of Rock Mechanics and Mining Sciences. 46 (2): 315–325. Bibcode:2009IJRMM..46..315P. doi:10.1016/j.ijrmms.2008.06.003.

Worked examples

Example 1 — a first encounter with Mining rock mass rating

Start with the simplest possible case. Write down what Mining rock mass rating claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mining rock mass rating before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mining rock mass rating ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mining rock mass rating

In research: Mining rock mass rating appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mining rock mass rating in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mining rock mass rating is common in secondary-school and first-year university syllabi. It links to neighbouring topics Rock mass classification, so understanding it makes those chapters shorter.
In everyday life: Look for Mining rock mass rating outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

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Why does Mining rock mass rating matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

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Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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