K-independent hashing

For the linguistics formalism, see Q-systems.

The Q-system for rock mass classification is developed by Barton, Lien, and Lunde. It expresses the quality of the rock mass in the so-called Q-value, on which are based design and support recommendations for underground excavations.

The Q-value is determined with

$Q=\frac{RQD}{J_n}\times \frac{J_r}{J_a}\times \frac{J_w}{SRF}$

The first term RQD (Rock Quality Designation) divided by J_n (joint set number) is related to the size of the intact rock blocks in the rock mass. The second term J_r (joint roughness number) divided by J_a (joint alteration number) is related to the shear strength along the discontinuityTemplate:Disambiguation needed planes and the third term J_w (joint water parameter) divided by SRF (stress reduction factor) is related to the stress environment on the intact rock blocks and discontinuities around the underground excavation.

A multiplication of the three terms results in the Q parameter, which can range between 0.00006 for an exceptionally poor to 2666 for an exceptionally good rock mass. The numerical values of the class boundaries for the different rock mass qualities are subdivisions of the Q range on a logarithmic scale.

The Q-value determines the quality of the rock mass, but the support of an underground excavation is based not only on the Q-value but is also determined by the different terms in the above equation. This leads to a very extensive list of classes for support recommendations.

Further reading

• Bieniawski, Z.T. "Engineering Rock Mass Classifications", John Wiley and Sons, New York, 1989
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• Pantelidis, L (2009). "Rock slope stability assessment through rock mass classification systems", International Journal of Rock Mechanics and Mining Sciences, 46(2), (315–325).

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See also

• Rock Structure Rating
• Hoek-Brown failure criterion