Engineering Rock Mechanics

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

Drill core aualitv RQD (%)

t25 25-50 50-75 75-90 90-100

Rating: 3 8 13 17 20

Spacing of discontinuities

t60mm 60-2OOmm 200-600mm 0.6-2m >2m

Rating: 5 8 10 15 20

Condition of discontinuities

Use Table (B), or the following guidelines

Soft gouge Slickensided Slightly rough Slightly rough Very rough

> 5 mm thick surfaces or surfaces, surfaces, surfaces, no

or separation gouge i 5 rnm separation separation separation,

755, thick or <^1 mm, highly <^1 mm, unweathered

continuous separation weathered wall slightly wall rock, not

1-5 mm, rock weathered continuous

continuous wall rock

Rating: 0 10 20 25 30

(B) Guidelines for classification of discontinuities

Discontinuity length (persistence)

<l m 1-3 m 3-10 m 10-20 m 220 m

Rating: 6 4 2 1 0

Separation (aperture)

none ~ tO.l mm 0.1-1.0 mm 1-5 mm >5 m

Rating: 6 5 4 1 0

Roughness

very rough rough slightly rough smooth slickensides

Rating^6 5 3 1 0

Infilling (gouge)

hard filling soft filling

none t5 Ilun >5 nun <5 mm >5 mm

Rating: 6 4 2 2 0

Weathering

unweathered slightly moderately highly decomposed

weathered weathered weathered

Rating: 6 5 3 1 0