science

Rock mass classification

Rock mass classification 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 Rock mass classification rather than just read about it. In short: Rock mass classification systems are used for various engineering design and stability analysis. These are based on empirical relations between rock mass parameters and engineering applications, such as tunnels, slopes, foundations, and excavatability.

Key takeaways

Rock mass classification belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Rock mass classification to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rock mass classification from memory before moving on to harder problems.

Reference excerpt

Rock mass classification systems are used for various engineering design and stability analysis. These are based on empirical relations between rock mass parameters and engineering applications, such as tunnels, slopes, foundations, and excavatability. The first rock mass classification system in geotechnical engineering was proposed in 1946 for tunnels with steel set support.

Design methods In engineering in rock, three design strategies can be distinguished: analytical, empirical, and numerical. Empirical, i.e. rock mass classification, methods are extensively used for feasibility and pre-design studies, and often also for the final design.

Objectives The objectives of rock mass classifications are (after Bieniawski 1989):

Identify the most significant parameters influencing the behaviour of a rock mass. Divide a particular rock mass formulation into groups of similar behaviour – rock mass classes of varying quality. Provide a basis of understanding the characteristics of each rock mass class Relate the experience of rock conditions at one site to the conditions and experience encountered at others Derive quantitative data and guidelines for engineering design Provide common basis for communication between engineers and geologists

Benefits The main benefits of rock mass classifications:

Improve the quality of site investigations by calling for the minimum input data as classification parameters. Provide quantitative information for design purposes. Enable better engineering judgement and more effective communication on a project. Provide a basis for understanding the characteristics of each rock mass

Rock mass classification systems

Systems for tunneling: Quantitative Rock Mass Rating (RMR) Q-system Geological Strength Index Mining rock mass rating (MRMR)

Other systems: Qualitative Size Strength classification

Systems for slope engineering Slope Mass Rating (SMR), Continuous Slope Mass Rating and Graphical Slope Mass Rating Rock mass classification system for rock slopes Slope Stability Probability Classification (SSPC) Q-slope

Earlier systems Rock load classification method The Rock load classification method is one of the first methodologies for rock mass classification for engineering. Karl von Terzaghi developed the methodology for tunnels supported by steel sets in the 1940s. By many regarded as obsolete as ideas about rock and rock mass mechanical behavior have since further developed and the methodology is not suitable for modern tunneling methods using shotcrete and rock bolts. Reference: Terzaghi, K. (1946). "Rock defects and loads on tunnel supports". In Proctor, R.V.; White, T. (eds.). Rock Tunnelling with Steel Supports. Youngstown, Ohio: Commercial Shearing and Stamping Co. pp. 15–99. also in Soil Mechanics Series 25, publication 418. Harvard University, Graduate School of Engineering. Stand-up time classification The Stand-up time classification by Lauffer is often regarded as the origin of the New Austrian Tunnelling Method (NATM). The original system as developed by Lauffer is nowadays by many regarded as obsolete but his ideas are incorporated in modern rock mechanics science, such as the relation between the span of a tunnel and the stand-up time, and notably in the New Austrian Tunnelling Method. Reference: Lauffer, H. (1958). "Gebirgsklassifizierung für den Stollenbau" [Mountain classification for the gallery construction]. Geology Bauwesen (in German). 74 (1): 46–51. Rock Quality Designation The Rock Quality Designation index was developed by Deere in the 1960s to classify the quality of a rock core based on the integrity of borehole cores. Nowadays the classification system itself is not very often used, but the determination of the RQD as index for rock core quality is standard practice in any geotechnical rock drilling, and is used in many, more recent, rock mass classification systems, such as RMR and Q-system (see above). Rock Structure Rating (RSR) The Rock Structure Rating system is a quantitative method for describing quality of a rock mass and appropriate ground support, in particular, for steel-rib support, developed by Wickham, Tiedemann and Skinner in the 1970s.

See also Slope Mass Rating Rock mechanics Geotechnical investigation Geotechnical engineering ISRM classification Slope stability, Slope stability analysis Classification of rocks

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. Palmstrom, A.; Broch, E. (2006). "Use and misuse of rock mass classification systems with particular reference to the Q-system". Tunnelling and Underground Space Technology. 21 (6): 575–593. Bibcode:2006TUSTI..21..575P. doi:10.1016/j.tust.2005.10.005. 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. Singh, B.; Goel, R.K. (1999). Rock Mass Classification: A Practical Approach in Civil Engineering. Elsevier Science. p. 282. ISBN 978-0-08-043013-3. Singh, B.; Goel, R.K. (2006). Tunnelling in Weak Rocks. Geo-Engineering. Vol. 5. Elsevier Science. p. 512. ISBN 978-0-08-044987-6.

Worked examples

Example 1 — a first encounter with Rock mass classification

Start with the simplest possible case. Write down what Rock mass classification 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 Rock mass classification 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 Rock mass classification 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 Rock mass classification

In research: Rock mass classification 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 Rock mass classification 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: Rock mass classification is common in secondary-school and first-year university syllabi. It links to neighbouring topics Rock mass classification, Rocks, so understanding it makes those chapters shorter.
In everyday life: Look for Rock mass classification 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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How to study Rock mass classification in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rock mass classification means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Rock mass classification out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rock mass classification in simple terms?

Why does Rock mass classification 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.

How should I study Rock mass classification?

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.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Rock mass classification.