Engineering Rock Mechanics

Appendix C: Rock mass classification tables - RMR and Q 499

Joint Alteration Number (J,)

(i) Rock wall contact

0.75

1.0

2.0

(a) Tightly healed, hard, non-softening,

impermeable filling, i.e. quartz or epidote

(b) Unaltered joint walls, surface staining only

(e) Slightly altered joint walls. Non-softening

mineral coatings, sandy particles, clay-free

disintegrated rock, etc.

fraction (non-softening)

coatings, i.e. kaolinite, mica. Also chlorite,

talc, gypsum, and graphite, etc., and small

quantities of swelling clays (discontinuous

coatings, 1-2 mm or less in thickness)

3.0

4.0

(d) Silty or sandy clay coatings, small clay

(e) Softening or low-friction clay mineral

(ii) Rock wall contact b@re 10 cm shear

4.0 (f) Sandy particles, clay-free disintegrated rock,

6.0 (g) Strongly over-consolidated, non-softening

etc.

clay mineral fillings (continuous, t5 mm in

thickness)

softening, clay mineral fillings (continuous,

<5 mm in thickness)

(continuous, <5 mm in thickness). Value of .I,

depends on percentage of swelling clay-sized

particles, and access to water, etc.

8.0 (h) Medium or low over-consolidation,

8.0-12.0 (j) Swelling clay fillings, i.e. montmorillonite

(iii) No rock wall contact when sheared
6.0, 8.0
or 8.0-12.0

(k) Zones or bands of disintegrated or rock and

clay - see (g), (h), (j) for description of clay

condition

fraction (non-softening)

see (g), (h), (j) for description of clay

condition

5.0 (1) Zones or bands of silty clay, small clay

10.0,13.0
or 13.0-20.0

(m) Thick, continuous zones or bands of clay -

25-35"

25-30"

20-25"

8-16'

25-30"

16-24'

12-16'

6-12"

6-24"

*Values of @r are intended as an approximate guide to the
properties of the alteration products, if present.

mineralogical