Engineering Rock Mechanics

498

Q-system of Rock Mass Classification

Appendix C: Rock mass classification tables - RMR and Q

RQD Jr Jw

Q=- x-x-

J,, J, SRF

Rock Quality Designation (RQD)

25-50 (b) Poor
50-75 (c) Fair

90-100 (e) Excellent

0-25 (a) Verypoor

75-90 (d) Good

Note: Where RQD is reported or measured as 10 (including 0), a nominal value
of 10 is used to evaluate Q. RQD intervals of 5, i.e. 100, 95, 90, etc., are
sufficiently accurate.

Joint Set Number (J,)

0.5-1.0 (a) Massive, none or few joints

2 (b) One joint set

3 (c) One joint set plus random

4 (d) Two joint sets

6 (e) Two joint sets plus random

9 (f) Three joint sets

12 (g) Three joint sets plus random

15 (h) Four or more joint sets, random, heavily jointed 'sugar cube', etc.

20 (j) Crushed rock, earth-like

Note: For intersections, use (3.0 x Jn); for portals, use (2.0 x Jn).

Joint Roughness Number (.I,)

4

3

2.0

1.5

1.5

1.0

0.5

1.0

1.0

(i) Rock wall contact and

(ii) Rock wall contact before 10 cm shear

(a) Discontinuous joint

(b) Rough or irregular, undulating

(c) Smooth, undulating

(d) Slickensided, undulating

(e) Rough or irregular, planar

(f) Smooth, planar

(g) Slickensided, planar intermediate-scale

(h) Zone containing clay minerals thick enough to prevent rock

(j) Sandy, gravelly, or crushed zone thick enough to prevent rock

small-scale

scale

increasing

I

(iii) No rock wall contact when sheared

wall contact

wall contact

Notes: Add 1.0 if the mean spacing of the relevant joint set is greater than 3 m.

J, = 0.5 can be used for planar slickensided joints having lineation,

provided the lineations are favourably orientated.

Descriptions (b) to (g) refer to small-scale features and intermediate-scale

features, in that order.

* Barton, N., Lien R. and Lunde J. (1974) Engineering classification of rock masses for

the design of tunnel support. Rock Mech., 6, 18S236.