Engineering Rock Mechanics

Q-system 195

hp 20 - 45

Table 12.1 (cont)

I Suh Dsmcndisullr to Nd ui8 i

C.EFFECT OF DISCONTINUITY ORIENTATIONS IN TUNNELLING

Ihp45-90 Ihpo-20

FROCK MASS CIASSES

SI no. I I I If

rand-uptim 2Oyrforl5mapnu IyrfalOmw

Fur Vay unfavourabk I

D. RATINQ ADJUSTMENT FOR DISCWNUIW ORlENTAllONS

• 
  


• 
  

  OnenlahOns of D~sconunuluu Very Favounblc Favowable Fer k -
  Tunnels & mines 0 -2 -5 -10 -12
  Raungr Foundaoons 0 -2 1 -I5 -25
  Slop 0 -5 -25 -50 M)
  E. ROCK MASS CLASSES DETERMINED FROM TOTAL runffis
  RUIng 100-81 80-61 60-41 40-21 00
  Clus no I 11 111 N V
  Descnpuon Vuygaodrcck Gmdmk Pan mek Poad Vaypoornuk -

  
  

RMR = ~(ciassification parameters) + discontinuity orientation adjustment

In Section A of Table 12.1, with the first five of the classification
parameters and their ratings, the parameters are grouped in five classes,
each one covering a range of values appropriate to that parameter. When
assessing a given rock mass, one establishes into which of these groups the
parameter lies, and then sums the resulting numerical ratings for the five
parameters.
In Section B of Table 12.1, there are ratings for discontinuity character-
istics. The orientation of the discontinuities becomes progressively more
important from tunnels and mines, through foundations, to slopes, Sections
C and D.
In Sections E and F of the table, the rock mass classes are given with a
description from ‘very good rock‘ through to ‘very poor rock‘, with
estimates for tunnel stand-up time and the Mohr-Coulomb strength
parameters of cohesion and friction angle for the rock mass.
Despite the simplicity of approach when dealing with complex rock
masses, considerable engineering benefit has accrued through the applica-
tion of this classification scheme and the resultant thinking that it has provoked.
Bieniawski (1989) mentions 351 case histories covering 15 years.

12.2 Q-system

In a similar way to the RMR system, the Q-rating is developed by assigning

values to six parameters. These are: