Rock mass classification systems - Geotechnical Investigation and Design Tables - page 231

Table 18.11 Volumetric joint rock (adapted from Barton, 2006).
Volumetric joint count ( J v ) no./m 3

Block sizes RQD RQD quality

Range Likely

Massive 1

Excellent

Large 1-3 4 100%

Medium

3-10

4-8 90%-100% Excellent

8-12 75%-90% Good

Small

12-20
20-27

50%-75%
25%-50%

Fair
poor

10-30

27-32 10%-25%

Very poor

Very small >30

32-35 0%-10%

18.12 Relative frictional strength
•

The ratio of the joint roughness number and the alteration number represents the
inter - block shear strength.

Table 18.12 Relative frictional strength from joint roughness and alteration (Barton et al., 1974).

Parameter/
symbol

Description Value

Rock wall contact Micro-Surface Macro-Surface

Any
Rough or irregular
Smooth,
Slickenslided
Rough or irregular
Smooth,
Slickenslided

Discontinuous
Undulating
Undulating
Undulating
Planar
Planar
Planar

4.0
3.0
2.0
1.5
1.5
1.0
0.5

Joint
roughness
number
J r

Rock - wall
contact and
contact before
10 cm shear

None when
sheared

Zone contains minerals or crushed zone thick enough to
prevent rock - wall contact

1.0

Rock wall contact Particles Filling Fillings type

f

r

Tightly healed, hard,
non softening,
impermeable
Unaltered joint walls,
none

Quartz 35 ° 0.75

Joint
alteration
number
J a

No mineral
fillings, only
coatings

Surfacing staining only 25-35 ° 1.0

Sandy particles, clay
free disintegrated rock

25-30 °

2.0

( Continued )