Q classification

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 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 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 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)

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)

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)