Select Rock Mass Properties



RQD (%)


Joint set number Jn
A Massive, no or few joints 0.5-1 (0.75)
B One joint set 2
C One joint set plus random joints 3
D Two joint sets 4
E Two joint sets plus random joints 6
F Three joint sets 9
G Three joint sets plus random joints 12
H Four or more joint sets, random heavily jointed“ sugar cube”, etc 15
J Crushed rock, earth like 20


Joint Roughness Number Jr
Rock-wall contact, and
Rock-wall contact before 10 cm of shear movement
A Discontinuous joints 4
B Rough or irregular, undulating 3
C Smooth, undulating 2
D Slickensided, undulating
1.5
E Rough, irregular, planar 1.5
F Smooth, planar 1
G Slickensided, planar 0.5
No rock-wall contact when sheared
H Zone containing clay minerals thick enough to prevent rock-wall contact when sheared 1


Joint Alteration Number φr Ja
Rock-wall contact (no mineral fillings, only coatings)
A Tightly healed, hard, non-softening, impermeable filling, i.e., quartz or epidote. - 0.75
B Unaltered joint walls, surface staining only. 25-35°
1
C Slightly altered joint walls. Non-softening mineral coatings; sandy particles, clay-free disintegrated rock, etc.
25-30° 2
D Silty or sandy clay coatings, small clay fraction (non-softening).
20-25°
3
E Softening or low friction clay mineral coatings, i.e.,kaolinite or mica. Also chlorite,
talc gypsum, graphite, etc., and small quantities of swelling clays.
8-16°
4
Rock-wall contact before 10 cm shear (thin mineral fillings)
F Sandy particles, clay-free disintegrated rock, etc. 25-30°
4
G Strongly over-consolidated, non-softening, clay mineral fillings (continuous, but <5mm thickness). 16-24°
6
H Medium or low over-consolidation, softening, clay mineral fillings (continuous, but <5mm thickness). 12-16°
8
J
Swelling-clay fillings, i.e., montmorillonite (continuous, but <5mm thickness). Value of J depends on
percent of swelling clay-size particles.
6-12°
8-12
(10)
No rock-wall contact when sheared (thick mineral fillings)
K
Zones or bands of disintegrated or crushed rock. Strongly over-consolidated. 16-24°
6
L
Zones or bands of clay, disintegrated or crushed rock. Medium or low over-consolidation or softening fillings.
12-16°
8
M
Zones or bands of clay, disintegrated or crushed rock. Swelling clay.
J depends on percent of swelling clay-size particles.
6-12°
8-12

(10)
N
Thick continuous zones or bands of clay. Strongly over-consolidated.
12-16°
10
O
Thick, continuous zones or bands of clay. Medium to low over-consolidation.
12-16°
13
P
Thick, continuous zones or bands with clay. Swelling clay. Ja depends on percent of swelling clay-size particles.
6-12°
13-20

(16)


Joint Water Reduction Factor Jw
A Dry excavations or minor inflow ( humid or a few drips)
1.0
B Medium inflow, occasional outwash of joint fillings (many drips/”rain”)
0.66
C Jet inflow or high pressure in competent rock with unfilled joints
0.5
D Large inflow or high pressure, considerable outwash of joint fillings
0.33
E Exceptionally high inflow or water pressure decaying with time.
Causes outwash of material and perhaps cave.
0.2-0.1

(0.15)
F Exceptionally high inflow or water pressure continuing without noticeable decay.
Causes outwash of material and perhaps cave.
0.1-0.05

(0.075)


Stress Reduction Factor SRF
Weak zones intersecting the underground opening, which may cause loosening of rock mass
A Multiple occurrences of weak zones within a short section containing clay or chemically disintegrated, very loose surrounding rock (any depth), or long sections with incompetent (weak) rock (any depth). For squeezing, see 6L and 6M 10
B Multiple shear zones within a short section in competent clay-free rock with loose surrounding rock (any depth) 7.5
C Single weak zones with or without clay or chemical disintegrated rock (depth ≤ 50m) 5
D Loose, open joints, heavily jointed or “sugar cube”, etc. (any depth) 5
E Single weak zones with or without clay or chemical disintegrated rock (depth > 50m) 2.5
Competent, mainly massive rock, stress problems σc / σ1 σΘ / σc SRF
F Low stress, near surface, open joints >200 <0.01 2.5
G Medium stress, favourable stress condition 200-10 0.01-0.3 1
H High stress, very tight structure. Usually favourableto stability.May also be unfavourable to stability dependent on the orientation of stresses compared to jointing/weakness planes 10-5 0.3-0.4 0.5-2
(1.25)
J Moderate spalling and/or slabbing after > 1 hour in massive rock 5-3 0.5-0.65 5-50
(27.5)
K Spalling or rock burst after a few minutes in massive rock 3-2 0.65-1 50-200
(125)
L Heavy rock burst and immediate dynamic deformation in massive rock <2 >1 200-400
(300)
Squeezing rock: plastic deformation in incompetent rock under the influence of high pressure σΘ / σc SRF
M Mild squeezing rock pressure 1-5 5-10
(7.5)
N Heavy squeezing rock pressure >5 10-20
(15)
Swelling rock: chemical swelling activity depending on the presence of water SRF
O Mild swelling rock pressure 5-10
(7.5)
P Heavy swelling rock pressure 10-15
(12.5)