Restricted #_x000D_

Modifications to RMR for mining 49

Table 4.4: Rock Mass Rating System (After Bieniawski 1989).
A. CLASSIFICATION PARAMETERS AND THEIR RATINGS
Parameter Range of values
Strength Point-load For this low range -
of strength index >10 MPa 4 - 10 MPa 2 - 4 MPa 1 - 2 MPa uniaxial compressive
intact rock test is preferred
1 material Uniaxial comp. 5 - 25 1 - 5 <1
>250 MPa 100 - 250 MPa 50 - 100 MPa 25 - 50 MPa
strength MPa MPa MPa
Rating 15 12 7 4 2 1 0
Drill core Quality RQD 90% - 100% 75% - 90% 50% - 75% 25% - 50% < 25%

2 Rating 20 17 13 8 3
Spacing of discontinuities >2m 0.6 - 2 . m 200 - 600 mm 60 - 200 mm < 60 mm

3 Rating 20 15 10 8 5
Very rough surfaces Not Slightly rough surfaces Slightly rough Slickensided surfaces Soft gouge >5 mm thick
continuous No separation Separation < 1 mm surfaces or or
Condition of discontinuities (See Unweathered wall rock Slightly weathered walls Separation < 1 mm Gouge < 5 mm thick Separation > 5 mm
4 E) Highly weathered walls or Continuous
Separation 1-5 mm
Continuous
Rating 30 25 20 10 0
Inflow per 10 m tunnel None < 10 10 - 25 25 - 125 > 125
length (l/m)
Ground (Joint water press)/
water (Major principal ) 0 < 0.1 0.1, - 0.2 0.2 - 0.5 > 0.5
5
General conditions Completely dry Damp Wet Dripping Flowing
Rating 15 10 7 4 0
B. RATING ADJUSTMENT FOR DISCONTINUITY ORIENTATIONS (See F)
Strike and dip orientations Very favourable Favourable Fair Unfavourable Very Unfavourable
Tunnels & mines 0 -2 -5 -10 -12
Ratings Foundations 0 -2 -7 -15 -25
Slopes 0 -5 -25 -50
C. ROCK MASS CLASSES DETERMINED FROM TOTAL RATINGS
Rating 100 81 80 61 60 41 40 21 < 21
Class number I II III IV V
Description Very good rock Good rock Fair rock Poor rock Very poor rock
D. MEANING OF ROCK CLASSES
Class number I II III IV V
Average stand-up time 20 yrs for 15 m span 1 year for 10 m span 1 week for 5 m span 10 hrs for 2.5 m span 30 min for 1 m span
Cohesion of rock mass (kPa) > 400 300 - 400 200 - 300 100 - 200 < 100
Friction angle of rock mass (deg) > 45 35 - 45 25 - 35 15 - 25 < 15
E. GUIDELINES FOR CLASSIFICATION OF DISCONTINUITY conditions
Discontinuity length (persistence) Rating <1m 1-3m 3 - 10 m 10 - 20 m > 20 m
6 4 2 1 0
Separation (aperture) None < 0.1 mm 0.1 - 1.0 mm 1 - 5 mm > 5 mm
Rating 6 5 4 1 0
Roughness Very rough Rough Slightly rough Smooth Slickensided
Rating 6 5 3 1 0
Infilling (gouge) None Hard filling < 5 mm Hard filling > 5 mm Soft filling < 5 mm Soft filling > 5 mm
Rating 6 4 2 2 0
Weathering Unweathered Slightly weathered Moderately Highly weathered Decomposed
Ratings 6 5 weathered 1 0
3

F. EFFECT OF DISCONTINUITY STRIKE AND DIP ORIENTATION IN TUNNELLING**

Strike perpendicular to tunnel axis Strike parallel to tunnel axis
Drive with dip - Dip 45 - 90 Drive with dip - Dip 20 - 45 Dip 45 - 90 Dip 20 - 45
Very favourable Favourable Very unfavourable Fair
Drive against dip - Dip 45-90 Drive against dip - Dip 20-45 Dip 0-20 - Irrespective of strike
Fair Unfavourable Fair

* Some conditions are mutually exclusive . For example, if infilling is present, the roughness of the surface will be overshadowed by the influence of

the gouge. In such cases use A.4 directly.

** Modified after Wickham et al (1972).

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Preliminary RMR Classification for CP 1

Parameter Rating Comment
UCS = 7.6 MPa (BH RD-FP-BH2)
Rock strength 12
UCS = 36.3 MPa (NCBH-20A)
RQD = 17 (BH RD-FP-BH2)
RQD 13
RQD = 41 (NCBH-20A)
Spacing of Discontinuities 11 Spacing 60 mm to 200 mm
length, 1 length 3 to 10 m
separation 3 0.1 mm to 1.0 mm
Condition of Discontinuities Roughness 4 15 Rough
Infilling 2 None
Weathering 5 Moderately Weathered
Water 10 Wet
Joint orientation -5 Unfavourable
RMR = 56 Poor

Preliminary RMR Classification for CP 3

Parameter Rating Comment
UCS = NA (NCBH-25)
Rock strength 4
UCS = 31.6 MPa (NCBH-25A)
RQD = 0 (NCBH-25)
RQD 3
RQD = 26 (NCBH-25A)
Spacing of Discontinuities 5 Spacing < 60 mm
length, 2 length 3 to 10 m
separation 4 0.1 mm to 1.0 mm
Condition of Discontinuities Roughness 5 20 Rough
Infilling 6 None
Weathering 3 Moderately Weathered
Water 7 Wet
Joint orientation -10 Unfavourable
RMR = 29 Poor

Preliminary RMR Classification for CP 4

Parameter Rating Comment
UCS = 74.8 MPa (RD-FP-BH-14)
Rock strength 7
UCS = NA (NCBH-27A)
RQD = 100 (RD-FP-BH-14)
RQD 17
RQD = 82 (NCBH-27A)
Spacing of Discontinuities 10 Spacing 200 mm to 600 mm
length, 4 length 1 to 3 m
separation 5 < 0.1 mm
Condition of Discontinuities Roughness 5 25 Rough
Infilling 6 None
Weathering 5 Slightly Weathered
Water 10 Wet
Joint orientation -5 Unfavourable
RMR = 64 Good
 Restricted #_x000D_

Preliminary RMR Classification for CP 5

Parameter Rating Comment
UCS = 20.5 MPa (NCBH-29)
Rock strength 4
UCS = 27.5 MPa (NCBH-29A)
RQD = 11 to 40 (NCBH-29)
RQD 3
RQD = 0 to 47 (NCBH-29A)
Spacing of Discontinuities 5 Spacing < 60 mm
length, 2 length 3 to 10 m
separation 4 0.1 mm to 1.0 mm
Condition of Discontinuities Roughness 5 20 Rough
Infilling 6 None
Weathering 3 Moderately Weathered
Water 7 Wet
Joint orientation -10 Unfavourable
RMR = 29 Poor
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Classification of individual parameters used in the Tunnelling Quality Index Q

(After Barton et al 1974).

DESCRIPTION VALUE NOTES

1. ROCK QUALITY DESIGNATION RQD

A. Very poor 0 - 25

B. Poor 25 - 50 1. Where RQD is reported or measured as <= 10 (including 0), a

nominal value of 10 is used to evaluate Q.
C. Fair 50 - 75

D. Good 75 - 90 2. RQD intervals of 5, i.e. 100, 95, 90 etc. are sufficiently accurate

E. Excellent 90 - 100

2. JOINT SET NUMBER Jn

A. Massive, no or few joints 0.5 - 1.0

B. One joint set 2

C. One joint set plus random 3

D. Two joint sets 4

1. For intersections use (3.0 Jn)
E. Two joint sets plus random 6
2. For portals use (2.0 Jn)
F. Three joint sets 9

G. Three joint sets plus random 12

Four or more joint sets, random,
H. 15
heavily jointed, 'sugar cube', etc.
J. Crushed rock, earthlike 20

3. JOINT ROUGHNESS NUMBER Jr

a. Rock wall contact

b. Rock wall contact before 10 cm shear

A. Discontinuous joints 4

B. Rough and irregular, undulating 3

C. Smooth undulating 2
1. Add 1.0 if the mean spacing of the relevant joint set is greater than 3
D. Slickensided undulating 1.5 m.

E. Rough or irregular, planar 1.5 2. Jr = 0.5 can be used for planar, slickensided joints having lineations,
provided that the lineations are oriented for
F. Smooth, planar 1.0 minimum strength.
G. Slickensided, planar 0.5

c. No rock wall contact when sheared

Zones containing clay minerals thick enough to prevent rock 1.0
H.
wall contact (nominal)
Sandy, gravely or crushed zone thick enough to prevent rock 1.0
J.
wall contact (nominal)
4. JOINT ALTERATION NUMBER Ja Ør degrees (approx.)

a. Rock wall contact

Tightly healed, hard, non-softening,
A. 0.75
impermeable filling
B. Unaltered joint walls, surface staining only 1.0 25 - 35

Slightly altered joint walls, non-softening mineral coatings, Values of Ør, the residual friction angle, are intended as an
C. 2.0 25 - 30
sandy particles, clay-free disintegrated rock, etc. approximate guide to the mineralogical properties of the alteration
products, if present.
Silty-, or sandy-clay coatings, small clay- fraction (non-
D. 3.0 20 - 25
softening)
Softening or low-friction clay mineral coatings, i.e. kaolinite,
mica. Also chlorite, talc, gypsum and graphite etc., and small
E. 4.0 8 - 16
quantities of swelling clays. (Discontinuous coatings, 1 - 2
mm or less)

b. Rock wall contact before 10 cm shear

F. Sandy particles, clay-free, disintegrating rock etc. 4.0 25 - 30

Strongly over-consolidated, non-softening clay mineral
G. 6.0 16 - 24
fillings (continuous < 5 mm thick) Values of Ør, the residual friction angle, are intended as an
Medium or low over-consolidation, softening clay mineral approximate guide to the mineralogical properties of the alteration
H. 8.0 12 - 16 products, if present.
fillings (continuous < 5 mm thick)

Swelling clay fillings, i.e. montmorillonite, 8.0 - 12.0

J. (continuous < 5 mm thick). Values of Ja depend on percent of 8.0 - 12.0 6 - 12
swelling clay-size particles, and access to water.

c. No rock wall contact when sheared

K. 6.0
Zones or bands of disintegrated or crushed rock and clay
L. (see G, H and J for clay conditions) 8.0

M. 8.0 - 12.0 6 - 24 Values of Ør, the residual friction angle, are intended as an
Zones or bands of silty- or sandy-clay, small 5.0 clay approximate guide to the mineralogical properties of the alteration
N. 5.0 products, if present.
fraction, non-softening

O. 10.0 - 13.0
Thick continuous zones or bands of clay (see G.H and J for
P. clay conditions) 6.0 - 24.0
 Thick continuous zones or bands of clay (see G.H and J for
clay conditions) Restricted #_x000D_

R. 6.0 - 24.0
 Restricted #_x000D_

Approx. Water Pressure

5. JOINT WATER REDUCTION Jw
kgf/cm2
A. Dry excavation or minor inflow i.e. < 5 l/m locally 1.0 < 1.0
Medium inflow or pressure, occasional outwash of joint
B. 0.66 1.0 - 2.5
fillings
Large inflow or high pressure in competent rock with unfilled Factors for C to F are crude estimates;
C 0.5 2.5 - 10.0 increase Jw if drainage installed.
joints
D. Large inflow or high pressure 0.33 2.5 - 10.0 Special problems caused by ice formation are not considered.
Exceptionally high inflow or pressure at blasting, decaying
E. 0.2 - 0.1 > 10.0
with time
F. Exceptionally high inflow or pressure 0.1 - 0.05 > 10.0

6. STRESS REDUCTION FACTOR SFR

a. Weakness zones intersecting excavation, which may cause

loosening of rock mass when tunnel is excavated

Multiple occurrences of weakness zones containing clay

A. or chemically disintegrated rock, very loose surrounding rock 10.0 Reduce these values of SRF by 25 - 50% but
any depth) only if the relevant shear zones influence do
not intersect the excavation
Single weakness zones containing clay, or chemically
B. 5.0
distegrated rock (excavation depth < 50 m)

Single weakness zones containing clay, or chemically

C. 2.5
distegrated rock (excavation depth > 50 m)

Multiple shear zones in competent rock (clay free), loose

D. 7.5
surrounding rock (any depth)

Single shear zone in competent rock (clay free). (depth of

E. 5.0
excavation < 50 m)

Single shear zone in competent rock (clay free). (depth of

F. 2.5
excavation > 50 m)

Loose open joints, heavily jointed or 'sugar cube', (any

G. 5.0
depth)

b. Competent rock, rock stress problems σc/σ1 σtσ1

H. Low stress , near surface 2.5 > 200 > 13
For strongly anisotropic virgin stress field (if measured):
J. Medium Stress 1.0 200 - 10 13 - 0.66 when 5 < s1/s3 < 10, reduce sc to 0.8 sc and st to 0.8 st.
when s1/s3 > 10, reduce sc to 0.6 sc and st to 0.6 st
High stress, very tight structure (usually favourable to sc - unconfined compressive strenth
K. 0.5 - 2.0 10 - 5 0.66 - 0.33
stability, may be unfavourable to wall stability) st = tensile strength (point load)
s1 and s3 are the major and minor principal stresses
L. Mild Rockburst (massive rock) 5.0 - 10.0 5 - 2.5 0.33 - 0.16

M. Heavy Rockburst (Massive rock) 10.0 - 20.0 < 2.5 <0.16

c. Squeezing rock, plastic flow of incompetent rock under

influence of high rock pressure Few case records available where depth of
crown below surface is less than span width.
N. Mild squeezing rock pressure 5 - 10 Suggest SRF increase from 2.5 to 5 for such
cases (see H).
O. O.Heavy squeezing rock pressure 10 - 20 10 - 20

d. Swelling rock, chemical swelling activity depending on

presence of water ###
P. Mild swelling rock pressure 5 - 10 Mild swelling rock pressure
R. Heavy swelling rock pressure 10 - 15 Heavy swelling rock pressure
ADDITIONAL NOTES ON THE USE OF THESE TABLES

When making estimates of the rock mass Quality (Q), the following guidelines should be followed in addition to the notes listed in the tables:
1. When borehole core is unavailable, RQD can be estimated from the number of joints per unit volume, in which the number of joints per metre for each joint set are added. A simple
relationship can be used to convert this number to RQD for the case of clay free rock masses: RQD = 115 - 3.3 Jv (approx.), where Jv = total number of joints per m3 (0 < RQD < 100
for 35 > Jv > 4.5).

2. The parameter Jn representing the number of joint sets will often be affected by foliation, schistosity, slaty cleavage or bedding etc. If strongly developed, these parallel 'joints' should
obviously be counted as a complete joint set. However, if there are few 'joints' visible, or if only occasional breaks in the core are due to these features, then it will be more
appropriate to count them as 'random' joints when evaluating Jn.

3. The parameters Jr and Ja (representing shear strength) should be relevant to the weakest significant joint set or clay filled discontinuity in the given zone. However, if the joint set or
discontinuity with the minimum value of Jr / Ja is favourably oriented for stability, then a second, less favourably oriented joint set or discontinuity may sometimes be more significant,
and its higher value of Jr / Ja should be used when evaluating Q. The value of Jr/Ja should in fact relate to the surface most likely to allow failure to initiate.

4. When a rock mass contains clay, the factor SRF appropriate to loosening loads should be evaluated. In such cases the strength of the intact rock is of little interest. However, when
jointing is minimal and clay is completely absent, the strength of the intact rock may become the weakest link, and the stability will then depend on the ratio rock-stress/rock-strength.
A strongly anisotropic stress field is unfavourable for stability and is roughly accounted for as in note 2 in the table for stress reduction factor evaluation.

5. The compressive and tensile strengths (sc and st) of the intact rock should be evaluated in the saturated condition if this is appropriate to the present and future in situ conditions. A
very conservative estimate of the strength should be made for those rocks that deteriorate when exposed to moist or saturated conditions.
 Restricted #_x000D_

Barton Q Classification for AT1 CH 0+46.5~0+50m

Parameter Value Comment

Rock Quality Designation RQD = 82.5 Jv=7.5

Number of joint sets Jn = 12 Three joint sets plus random

Joint roughness factor Jr = 1.5 Slickensided undulating

Silty-, or sandy-clay coatings, small clay- fraction (non-

Joint alteration factor Ja = 3
softening)

Dry excavation or minor inflow i.e. < 5 l/m

Joint water factor Jw = 1
locally

Single weakness zones containing clay, or chemically

Stress reduction factor SRF = 2.5
distegrated rock (excavation depth > 50 m)

Q value Q= 1.38 Very Poor