Engineering Rock Mechanics

194 Rock mass classification

parameters relating to the geometry and mechanical condition of the rock
mass are used. In the case of the RMR system, these are:

(a) the uniaxial compressive strength of the intact rock;

(c) discontinuity spacing;
(d) condition of discontinuity surfaces;
(e) groundwater conditions; and
(f) orientation of discontinuities relative to the engineered structure.

The way in which these parameters are used to provide an overall rating
is shown in Table 12.1.

(b) RQD;

Table 12.1 The rock mass rating system (after Bieniawski, 1989)
Rock Mass Rating System
A. CLASSIFICATION PARAMETERS AND THEIFI mnffis
I P-ICC I Ragesofnlua
1

quality RQD

Condition of

dirontinuitiu

Rating

Inflow psi 1Om

NMCI lcnglh

(hin)

(joint warn

principal smn)

conditions

ForIbislawrangs.

>IO I 4-10 I 2-4 I I - 2 uniaxial compressiw

Lest is pnfentd

~

I5 12 7 4 210

90- 100 75 .go 50.75 25 - 50 Q5

2011s1101 8 I5

I I I I

30 I 25 20 I IO 0

0 I 4.1 10.1-0.2 I 0.2-0.5 1 >os

I Ratlns I IS 10 7 4 0

c UIDEUNES FOR CLASSIFICATION OF DISCONTINUN CONMnONS

PWMCIU Ratings

Dimlinuity length (~~) <Im I-3m 3-10111 I0-2hn >zon,

c I I I I