Identification and classification of rock

Identification and classification of rock is covered by International Standard EN ISO 14689, which is divided into two parts covering description and classification (Part 1) and data transfer (Part 2).8 EN ISO 14689 is referenced extensively in EN 1997-2.

4.4.1 Rock description

Rock description according to EN ISO 14689-1 is based on the terms published by the International Society of Rock Mechanics (ISRM),9 in preference to those in BS 5930.

Two stages are identified in the description of rocks: rock material and rock mass. The description of the rock material shall include colour, grain size, matrix, weathering and alteration effects, carbonate content, stability of rock material and unconfined compressive strength. For the rock mass terms include type of rocks, structure, discontinuities, weathering and groundwater.

4.4.2 Rock material strength

The strength of rock is described by the terms extremely weak, very weak, weak, medium strong, strong, very strong, and extremely strong and classified by the unconfined compressive strength qu measured in a laboratory strength test. See Figure 4.11.

Unconfined compressive strength qu (MPa)

Extremely weak

Very weak


Medium strong


Very strong

Extremely strong

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