Rock mass classification systems - Geotechnical Investigation and Design Tables - page 232

Table 18.12 ( Continued )

Parameter/
symbol

Description Value

Rock wall contact Particles Filling Fillings type

φ r

Slightly altered joint
walls, non softening
mineral coatings
Non softening

Silty or sandy - clay
coatings, small clay
fraction
Low friction clay
mineral coatings
ie Kaolinite, mica

No mineral
fillings, only
coatings

20-25 ° 3.0

Softening 8-16 ° 4.0

Sandy particles, clay -
free disintegrated rock
clay mineral
(continuous, but
5 mm thickness)
clay mineral fillings
(continuous, but
5 mm thickness)
Swelling - clay fillings
ie montmorillonite
(continuous, but
5 mm thickness)

25-30 ° 4.0

Strongly over-
consolidated non
softening fillings

Joint
alteration
number
J a

16-24 ° 6.0

Thin mineral
fillings.
Rock wall
contact before
10 cm shear

Medium or low
over-consolidation,
softening
Depends on access
to water and % of
swelling clay size
particles

12-16 ° 8.0

6-12 ° 8-12

Zones or bands Disintegrated or

crushed rock and clay
Silty or sandy clays

6-24 ° 6, 8 or

8-12
5.0

No rock wall
contact when
sheared (thick
mineral fillings)

Zones or bands,
small clay fraction
(non softening)

6-24 °

Thick continuous
zones or bands of clay

10,13
or
13-20

18.13 Active stress - relative effects of water, faulting,
strength/stress ratio

•

The active stress is the ratio of the joint water reduction factor and the stress
reduction factor.

•

The joint water reduction factor accounts for the degree of water seepage (Table
18.13).

18.14 Stress reduction factor
•

The stress reduction factor is a measure of (Table 18.14):
-

The loosening load where excavations occur in shear zones and clay bearing
rock,