Engineering Rock Mechanics

200 Rock mass classification

Using the rock mass parameters in each case to provide a quantitative
assessment of the rock mass, and utilizing experience gained from
previously excavated stable and unstable tunnels, design charts have been
constructed, as shown in Figs 12.1 and 12.2, for estimating 'stand-up time'
or support requirements. For a description of the complete technique for
establishing the support requirements, the reader is referred to Bieniawski
(1989), which expands on the fundamentals given here of the two
systems.
Attempts have been made to extend the classification system to slopes
(Romana, 1985). Naturally, the six parameters utilized in the RMR system are
relevant to slope stability, but the classification value needs to be adjusted
for different engineering circumstances. The way in which Professor
Romana numerically adjusted the RMR value was by considering the
following factors:
(a) F1 associated with parallelism between the slope and the discontinuity

(b) F2 related to the discontinuity dip for plane failure;

(c) F3 concerning the slope angle compared to the discontinuity dip angle;

(d) F4 relating to the method of excavation.

The classification value is then found from the formula

strike direction;

and

Table 12.3 indicates the numerical values of the four factors required to

adjust RMRBAslc to RMRsLOpE, together with the SMR classes, the types of

failure anticipated, and any remedial measures necessary to improve

stability.

Table 12.3 The SMR rating system (from Romana, 1985 and Bieniawski, 1989)

VW

1q - -.I >w 30-w 20-10. 10-5' <5'

P/T .=I 0.15 0.40 0.70 0.85 1.00

lei1 <w 20-w 90-35' 35-45' >45*

Fz 0.15 0.40 0.70 0.85 1.00

T F2 1 1 1 1 1

P Pi - B. >lo. 10-0- 0. 0--(-10.) c-10-

T R+R <llV 110-1w 2120.

P/T F3 0 -6 -25 -50 -60

T = (oppung IailuIo. 8. - ~2.~8 dip. &-iowdP.

-0 Very FevoraMe Fernable Far Unfauorable Unfavorable

P

T Iq-%-180.1

P

P

P - pluu flilure. 4 - skwa dip direaim. 9 - pM d@ dimckm.

SMR - RMR - (F, x h x hl + Fa

Tentative ~escriirion d SMR classes