Soil and rock terminology for description and classification for engineering purposes - Practical Engineering Geology - page 366

Table C5 Examples of other standard terminology in use for intact rock strength.

New Zealand Geotechnical Society (2005)

Strength UCS MPa Is (50) (MPa)

Extremely weak <1.0

-

Very weak 1 5

<1

Weak 5 - 20

Medium strong 20 - 50 1 - 2

Strong 50 - 100 2 - 5

Very strong 100 - 250 5 - 10

Extremely strong >250 >10

Australian Standard AS1726

Strength Is (50) (MPa)

Extremely low Generally N/A

Very low <0.1

Low 0.1 - 0.3

Medium 0.3 - 1

High 1 - 3

Very high 3 - 10

Extremely high >10

China National Standard (2009)

Strength UCS (MPa)

Extremely soft <5

-

Soft 5 15

Moderately 4 soft 15 - 30

Moderately hard 30 - 60

Hard >60

4 Term used in Chinese code (original translation) is

' secondly ' rather than ' moderately ' .

BS EN ISO 14689-1:2003 does not say what a joint is but de nes

discontinuity:

Discontinuity : surface which breaks the rock material continuity within
the rock mass and that is open or may become open under the stress
applied by the engineering work; the tensile or shear strength across or
along the surface is lower than that of the intact rock material.