Rock Mass Classification and Tunnel Reinforcement Selection Using The Q System Astm - Barton 1988 - HAVE BETTER VERSION CHECK
Rock Mass Classification and Tunnel Reinforcement Selection Using The Q System Astm - Barton 1988 - HAVE BETTER VERSION CHECK
Rock Mass Classification and Tunnel Reinforcement Selection Using The Q System Astm - Barton 1988 - HAVE BETTER VERSION CHECK
for every site and will be organized into an overall database. The data will provide the basis for
a detailed quantitative assessment of current design criteria of emergency spillways and will assist
in the development of any needed revisions.
I believe that Dr. Kirsten's idea of applying his erodibility index (expressed as N) to a rock
mass that forms an excavated spillway channel should be explored in our (SCS) assessment. Once
the data base is established from the spillway performance reports it would be productive to
determine an empirical relationship between J, and the relative dip angle and block shape for
hydraulic erosion of spillway channel beds. The analysis should be useful in our assessment of
design criteria for excavated rock emergency spillways.
Nick Barton'
This paper provides an analysis of the Q-system of rockmass characterization and tunnel support
selection. The 212 case records utilized in developing the Q-system (Barton et al, 1974) are
reviewed in detail, so that application to new projects can be related to the extensive range of
rock mass qualities, tunnel sizes, and tunnel depths that constitute the Q-system data base.
Ultimately, a potential user of a classification method will be persuaded of the value of a
particular system by the degree to which he can identify his site in the case records used to develop
the given method. The most comprehensive data base of the seven or eight classification systems
reviewed is utilized in the Q-system. This body of engineering experience ensures that support
designs will be realistic rather than theoretical, and more objective than can be the case when few
previous experiences are utilized to develop a support recommendation.
BARTON ON Q-SYSTEM 61
Name of
Classification
Originator
and Date
Country
of Origin
Applications
Rock Loads
Terzhagi (1946)
USA
Stand-Up-Time
Lauffer (1958)
Austria
tunneling
RQD
USA
RSR Concept
Wickham et al (1972)
USA
Geomechanics
(RMR System)
Q-System
Bieniawski (1973)
S. Africa
Barton et al (1974)
Norway
The NATM relies on performance monitoring for prediction and classification of ground
conditions. It is adapted to each new project based on previous experience. The classification is
also adapted during a single project based on performance monitoring. A particular classification
is therefore only applicable to the one case for which it was developed and modified, so use by
others on other projects may be difficult.
The NATM is essentially a design method in which the rock mass is allowed to yield only
enough to mobilize its optimum strength, by utilizing light temporary support. With correct timing
of final support, this initial yielding is arrested in time to prevent loss of strength. On occasion,
the desire to allow deformation to occur by installing canals of deformable material within the
shotcrete, and steel ribs with sliding joints, has resulted in loss of ground control and severe
damage to final concrete linings and bolt arrays (Barton, 1982).
Updating Case Records
Some of the support methods recommended by the above classification methods are quite labor
intensive and will need updating as new support methods become more generally available. For
example, the development of high strength, but highly ductile, steel fiber reinforced microsilica
shotcrete is a revolutionary advance in tunnel support. It can be applied by one robot operator and
one back-up person right at the tunnel face. The extra strength of this product removes the need
for mesh in shotcrete, and it has sufficient early strength to replace steel arches and cast concrete
under a large range of tunnelling conditions.
Comparison of RMR and
Q Systems
The two classification systems that appear to be in widest use in tunneling that do not rely on
performance monitoring (though they can be used in conjunction with monitoring) are the RMR
and Q systems. These two systems are therefore compared in some detail here.
Bieniawski (1976) rates the following six parameters in his RMR system:
I. Uniaxial compressive strength of rock material.
Drill core quality RQD.
Spacing of joints.
Condition of joints.
Groundwater conditions.
6. Orientation of joints.
In contrast, the Q-system (Barton et al, 1974) rates the following six parameters:
I. RQD.
BARTON ON 0-SYSTEM 63
Q=
(1)
where
RQD = rock quality designation (Deere et al, 1967),
J = joint set number,
J, = joint roughness number (of least favorable discontinuity or joint set),
J,, = joint alteration number (of least favorable discontinuity or joint set),
J. = joint water reduction factor, and
SRF = stress reduction factor.
The three pairs of ratios (RQD/J, J,/.1, and J./SRF) represent block size, minimum inter-block
shear strength, and active stress, respectively. These are fundamental geotechnical parameters.
It is important to observe that the values of J, and J relate to the joint set or discontinuity most
likely to allow failure to initiate. The important influence of orientation relative to the tunnel axis
is implicit.
Detailed descriptions of the six parameters and their numerical ratings are given in Table 2.
The range of possible Q values (approximately 0.001 to 1000) encompasses the whole spectrum
of rock mass qualities from heavy squeezing ground up to sound unjointed rock. The case records
examined included 13 igneous rock types, 26 metamorphic rock types, and 11 sedimentary rock
types. More than 80 of the case records involved clay occurrences. However, most commonly the
joints were unfilled and the joint walls were unaltered or only slightly altered.
The Q-system is more detailed than any of the other methods as regards the factors joint
roughness (or degree of planarity), joint alteration (filling), and relative orientation. The classification
of "least favorable features" (for J, and .1,,) represents one of the strongest features of the method.
It also seems to be a factor that is virtually ignored in the other classification schemes. For
example, in Bieniawski's RMR method, although data for all joint set and discontinuities are
collected, only the average data are incorporated in the numerical ratings. Furthermore, in the
RMR it is impossible to separately vary the degree of joint roughness and the degree of infilling,
as obviously may occur in practice.
BARTON ON Q-SYSTEM 65
64 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES
0 - 25
25 - 50
50 - 75
75 90
90 - 100
(J )
JD)
(Jr)
4
3
2
1.5
1.5
1.0
0.5
(J.)
(Or)
(approx.)
TABLE 2- (continued).
0.75
( - )
1.0
(25-35')
2.0
(25-30')
3.0
(20-25')
(8-16')
before
Sandy particles,clay-free
disintegrated rock etc.
4.0
Strongly over-consolidated
non-softening clay mineral
fillings (continuous,but
<5 mm thickness)
6.0
Medium or low over-consolidation,softening,clay mineral
fillings. (continuous but
<5mm thickness)
8.0
J. Swelling -clay fillings, i.e.
montmorillonite (continuous,
but <5mm thickness) Value of
J a depends on percent of swelling clay-size particles,and
access to water etc.
8 - 12
(c) No rock wall contact when sheared
K,L, Zones or bands of disint.
egrated or crushed rock
and clay(see G,H,J for
description of clay
condition)
N.
Zones or bands of siltyor sandy-clay,small clay
fraction (non-softening)
0,P, Thick,continuous zones
H.
or bands of clay(see G,
H,J for description of
clay condition)
6, 8,
or 8-12
(25-30')
(16-24')
(12-16')
(6-12')
(6-24')
5.0
10' 13 '
(6-24')
1.0
1.0
1.0
<1
0.66
1 - 2.5
0.5
2.5-10
0.33
2.5-10
0.2-0.1
>10
0.1-0.05
>10
66 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES
TABLE 2(continued).
E.
(SRF)
10
2.5
7.5
5.0
2.5
5.0
BARTON ON Q-SYSTEM 67
(SRF)
>200
'00-10
>13
13-0.66
2.5
1.0
10-5
0.66-.33
0.5-2
5-2.5
0.33-.16
02.5
<0.16
5-10
10-20
A considerable data base for developing the Q-system was provided by Cecil (1970), who
described numerous tunneling projects in Sweden and Norway, including detailed evaluations of
the rock, the jointing, the type of support, and the apparent stability. Figure 2 shows three examples
of Cecil's cases, and Table 5 gives the abbreviated descriptions of the key rock mass parameters
and describes the support actually used. Note that the alphabetic descriptions given in brackets in
Table 5 can be checked directly against the same letters given in Table 2. This convenient
shorthand method can be used during tunnel mapping, when writing conditions are unfavorable.
Examples of Tunnel Mapping
R.
5 - 10
10
15
Examples of some tunnel projects in which the Q-system has been used extensively in day-today follow-up mapping are shown in Figs. 3a and 3b. It will be noticed that the treatment of
crushed zones and major discontinuities shown in Figs. 3a and 3b is often on an individual basis.
The quality of the rock mass between the zones is a decisive factor in deciding between individual
"stitching" and general support.
One of the examples (Fig. 3b) is a tunnel excavated by a full-face tunnel boring machine
(TBM). The minimal disturbance caused by TBM excavation makes it particularly important to
map as close to the advancing face as possible (for optimal joint definition), followed by repeated
it
11
al
nnnnnnnnn
N11181111111111MINM
IN11611111111111111111=11
1111111110111M=MMI
116111111111111111
2281==MMI
IMIIIIIIIIIMMEMIII nnnMEMIN 8
11E111nn 11111111
INIMIIIM=IMOMMOOMI nnn =11=11111n11,n
11101111==n11n111n11MIIMMIIINn
161111111111/1/ sumwoommossoessammiss
1111
BONIFIIIMIIMIIIn12nnn
IIMMIINIMINMEMENIMOMMINI=M111
INmill11111111111113111111111M1111111111111
12.1
1111111111MMII
MUM
11
1111n 1111111
111 In11111111
CC
VI
MIMI
1..
"1:=;;;I:mr61
'=a0MMINIIIMMIIIII
.1111=NIMIIIIIIIIIMIIIMI
Ma IIIIIMEM
11 MOINE
111111nn
min
MOE
111111
MI
gamma
...m.
....rx====:::=E= mow
se
MOO
:.
ESR
Type of Excavation
11111111111111111M1 1111111111011011=1
1111111111111111111111111.1.1111 8
MI
in .1, PI
Alnnn111MIINIM
00 Ili
). 80
7
0.10=1=M11=1.n
1
9.11=111111119.1111111ONIMMIIII n
)1-4 g I
sr 0
BARTON ON 0-SYSTEM 69
0.1
aatt
"MI
Number
of Cases
ca. 3-5?
1.6
83
1.3
25
1.0
79
ca. 0.8?
mapping before permanent support is chosen. There will then be improved possibilities for
observing the character of narrow clay-bearing discontinuities. The effective RQD of the zone of
rock around a TBM excavated tunnel will generally be higher than that around a blasted tunnel
owing to the relatively slight disturbance of incipient joints and tight structures.
Figure 4 illustrates ten parallel (100 m long) sewage treatment caverns constructed near Oslo.
At the feasibility and planning stage, surface mapping and drill core analysis were interpreted in
terms of the Q-system parameters. Support requirements were predicted on this basis. During
construction, support decisions were also guided by the method outlined. The general improvement
in rock conditions as the parallel caverns advanced from the shale into the nodular limestone were
clearly reflected in the six parameters and support was reduced accordingly:
Shale: B 1.25 in c/c, L
3.5 m + S (mr) 12-15 cm
Nodular limestone: B 1.5 m c/c, L= 3.5 m+ S 5 cm
(B = bolting, c/c = spacing, L = length, S = shotcrete, mr = mesh reinforced)
a
,..._cam
The Q-system has also been used in the area of mine stability. In a recent assessment of stability
in two limestone mines with 13 to 15 m span rooms or drifts, respectively, the quality of the
limestone varied as follows:
OMISn1IMIN
UCIN=M11=1
UM.
IMEMINON
Q =
INEMIEMEMII
Unnn
0
1111111
essiuminn
UMW
11111
UOMMMMIN
111111 nn1
R, R
I 1.5
4 9
1 2
1
= 4 38 (fair -- good)
1
In the great majority of the drifts the quality was "good" (Q = 18 38). By comparing these
qualities with the permanently unsupported cases (Fig. 1, black circles) it was possible to
demonstrate satisfactory conditions for the great majority of the excavations. However, in places,
stability was apparently nearer the "temporary mine openings" category (ESR = 3-5, Table 1).
There were in fact limited areas in the mines where fall-out occurred from the pillars or walls. A
limited number of pillars in one of the mines were instrumented as a precaution.
1n
0 0 11111111111n1
0
11
80 100
e)
VS3 / NINS
An important area of application for the Q-system is the recognition of rock mass characteristics
required for safe operation of permanently unsupported openings. The relationship between the
maximum unsupported span and the Q-value is clearly seen in Fig. I. Detailed analysis of the
available case records reveals the following requirements:
BARTON ON Q-SYSTEM 71
TABLE 4-Support recommendations for the 38 categories shown in Fig. I (see Barton et al, 1974, 1975
TABLE 4-(continued).
Support
rate-
gory
I"
Cottilatonal factors
Ro
J.
SPAN
1,
.1
ESR
- -
-
- -
- -
4'
-
5 -
6 - -
Conditional factors
Ro,
J.
SPAN
=-
____
-
1,,
1a
ESR
Support
cute-
gory
Tvpe of .support
Notes
sblutg)
sblutg)
sblutg)
sblutg)
sblutg)
sblutg)
sblutg)
-
-
7'
-
g'
sblutg)
-
Note. The type of suppon to be used in categories I to 0 will depend on the
blasting technique. Smooth wall blasting and thorough barring-down
may remove the need for suppon. Rough-wall blasting may result in the
need for single applications of shotcrete, especially where the excavation
height is >25 m Future cast records should differentiate categories I
to 8.
.sblutg))
-
020
9
Biutg) 2.5-3 m
-
<20
Blutg) 2-3 in
- -
030
10
Biutg) 1.5-2 m
<30
- -
+ clm
13002-3 in
- -
030
II"
,_
13(tg) I 5-2 in
<30
+ clm
BItg) 2-3 m
-
030
12'
130g) 1.5-2 m
-
<30
elm
-
shorty)
I
'1.5
10
1
-
filing) 1.5-2 m
<1.5
010
I
Bang) 1.5-2 in
01.5
-
<10
13
I
-
Blutg) 1.5-2 ID
<1.5
<10
+ S 2-3 cm
1.11
Bitg) 1.5-2 in
015
010
-
+clm
I. II
130g)
1.5-2
m
015
<10
-
Id
+S(mr) 5-10 cm
I. III
<15
Biutg)
1.5-2
in
- -
+clm
I. II. IV
Bag) 1.5-2 in
>10
+clm
15
I. II, IV
- -
130g) 1.5-2 in
--10
+ S(mr) 5-10 cm
I, V, VI
Bug) 1.5-2 in
>15
- -
16'
+clm
See
I. V, VI
B(tg) 1.5-2 m
015
- note
+ S(an) 10-/5 cm
XII
I
sblutg)
- -
>30
(.0,31g)
I
- -
13(utg) 1-1.5 in
17
1
.-6 m B(utg) 1-1.5 m
-
<10
+S 2-3 cm
I
-
<6 ni S 2-3 cm
<10
I. Ill
_010 m B(tg) 1-1.5 m
-
>5
+clm
I
>5
-
<10 m Blutg) 1-1.5 m
+clm
10
I. III
B0g)
1-1.5
m
05
'110 in
-
+S 2-3 cm
I
5
-
<10 m B(utg) 1-1.5 m
+ S 2-3 cm
19
--
20'
See
note
XII
21
22
-.12.5
'--0.75
<l2.5
(>10, \
k<30 /
,10
<30
00.75
>0.75
>1.0
>1.0
'1.0
030
-
23
24
See
note
XII
>10
>0.5
010
>0.5
00.5
25
26
27
See
note
XII
>5
>0.25
>0.25
-=_0.25
-_
020 in
Type of support
B(tg) 1-2 m
+ SAO 10-15 cm
<20 mBItg) 1-1.5 m
+S(mr) 5-10 cm
035 in Bag) 1-2 m
+ S(mr) 20-25 cm
<35 in 130g) 1-2 m
-.- S(mr) 10-20 cm
-
B(utg) 1 m
+5 2-3 cm
S 2.5-5 cm
-
B(utg) 1 m
-
-
13tutg) I in
+clm
-
S 2.5-7.5 cm
-
B(utg) I m
+S(mr) 2.5-5 cm
B(utg) 1 m
15 m B(tg) 1-1.5 m
+S (me) 10-15 cm
<15 m B(utg) 1-1,5 IP
+ S( mr) 5-10 cm
'30 ni B0g) 1-1.5 m
+ S(mr) 15-30 cm
<30 m B(tg) 1-1.5 in
+ S(mr).10-15 cm
B(utg) I m
--
+ no or elm
--B(utg) 1 rn
+S(mr) 5 cm
130g) I m
-
+S(mr) 5 cm
-
BItg) 1 m
+ S1mr) 5-7.5 cm
B(utg) 1 m
+S 2.5-5 cm
-12m B(tg) I m
+S(mr) 7.5-10 cm
<I2m B(utg) 1 m
+S(mr) 5-7.5 cm
0-40
cm
>I2m CCA
+
Im
<I 2m S(mr) 10-20 cm
+ B(tg) I m
0-30m B(tg) I m
+S(mr) 30-40 cm
(.020, \ B(tg) 1 in
k<30 nil +S(mr) 20-30 cm
<20m B(tg) I m
+S(mr) 15-20 cm
CCA)sr) 30-100
cm
+ B(tg) I m
B(utg) I m
-
+S 2-3 cm
B(utg) 1 m
-
+S(mr) 5 cm
-
B0g) I m
+S(mr) 5 cm
Notes
I, II, IV
I, II
I. V, VI
I, II, IV
I
I
I
1
I
1
I, II, IV,
VII
I. V, VI
I, II, IV
I
1
1
VIII, X,
XI
I, IX
I, IX
I, IX
VIII, X,
XI
VIII, X,
XI
I, IV, V,
IX
I, II, IV,
IX
1. 11, IX
IV, VIII.
X, XI
-
BARTON ON Q-SYSTEM 73
TABLE 4(continued).
Conditional factors
RQD
1,
SPAN
5 "PP. '"
1,
!UM-
80ry
30
31
14
ESR
<5
>4
04, .1.5
<1.5
.',.20nt
<20m
02
<2
02
0--0.25
<2
00.25
<0.25
35
See
note
XII
<5
32
See
note
XII
33
.1,
:_-_-'15m
-0"15m
<15m
<15in
B(tg) I m
+S(mr) 5-12.5 cm
S(mr) 7.5-25 cm
CCA 20-40 cm
+ Bag) I m
CCA(sr) 30-50 cm
+ B0g) I in
B0g) I m
+ Simr) 40 60 cm
Bug) I m
+ Stmr) 20-40 cm
CCAlsr) 40-120 on
+B(tg) I in
IX
VIII, X,
XI
IX
IX
IX, X1
VIII, X,
XI
II. IV,
IX, XI
IX
IV. VIII.
X, X1
B0g) I ni
+ S(mr) 5-7.5 cm
S(mr) 7.5-15 cm
S(mr) 15-25 cm
CCA(sr) 20-60 cm
+130g) 1 rn
IX
Blig) I m
+ S(mr) 30-100 cm
CCAIsr) 60-2(0 cm
+ Bttg) I m
B(tg) I m
+ S(mr) 20-75 cm
CCAtst) 40-150 cm
+ B(tg) I m
cr)
III, IV, XI
IX
38
See
note
XIII
IX
Bttg) I m
+S(mr) 2.5-5 cm
S(mr) 5-10 cm
Slim) 7.5-15 cm
36
37
Notes
Type of support
B(tg) I in
+S 2.5-5 cm
S(rnri 5-7.5 cm
13(tg) 1 m
+S(nu) 5-7.5 cm
-0
IX
IX
VIII, X,
XI
II, IX,
XI
VIII, X,
XI, II
IX. III,
XI
VIII, X,
XI, III
IX
VIII. X.
XI
Slmr) 20-60 cm
Slot') 20-60 cm
+ B(tg) 0.5-10 m
IX
VIII, X.
XI
010m
010m
---
<10m
<10m
CCA(sr)100-300 cm
CCA(sr)100-300 cm
+130g) I m
S(mr) 70-200 cm
S(mr) 70-200 cm
+ B(tg) 1 m
IX
VIII, X,
II, XI
IX
VIII, X,
III. XI
-- spot bolting
= systematic bolting
= untensioned. grouted
= tensioned. (expanding shell type for competent rock masses, grouted
post-tensioned in very poor quality rock masses; see Note XI)
S
= shotcretc
(mr) = mesh reinforced
clm = chain link mesh
CCA = cast concrete arch
(sr)
= steel reinforced
B
(utg)
(tg)
w
0
IX
VIII. X
sh
If)
0.
TABLE 5-Comparison of support used and support recommended for three case records described b y Cecil (1970).
Case
No.
24
48
77
15 m length, overthrust
shear zone in schist, in
which there was a 3 cm
thick clay (non softening)
Shear
and graphite seam.
zone was 50-100 cm wide
and contained smooth,
slickensided graphitecoated joint surfaces,
1 joint set, 5-30 cm
Insignificant
spacing.
RQD = 10
water inflow.
Wedge-shaped roof fall.
3. Tailrace tunnel, Bergvattnet, Hydro, N.Sweden
(ref. Cecil 1970)
300 m length, massive
gneiss, few joints.
Planar, rough-surfaced,
unaltered Joints.
3 m
spacing.
Insignificant
RQD . 100
water inflow.
Minor overbreak, no
falls or slides.
3. Wine and liquor storage
rooms.
Stockholm (ref.
Cecil 1970).
12.5
m )
6.5
( m)
60
Rock bolts,
wire mesh and
shotcrete
RQD
L._1.r.
,w
.3
J
SRF
n
(Code :Tables 1 to 6)
60
1.0
6
31
( 4K
)
2E
ESR
Category 22
=13 1 m
+S(mr)
2.5-5 cm
1.0
2.5
SA
( 6C.)
1.3 1.6
6.5
4.5
50
Rock bolts,
wire mesh and
two shotcrete
applications
1.0
10
(IA)
2B
(3H)
40
10
20
24.5
7.8
Category 31
.8 1 m
+S(mr) 5 cm
1.0
5
(SA)
68
0.10 1.6
50 spot bolts
in about
300 a of
100
chamber
1.0
SPAN Estimate of
ESR permanent
roof support
4.1
Category 0,5
=None or sb
5
1.0
1.3
2.5
18
1E
( -)
2A
3E
( --)
4B
5A
(--)
6H
200
1.3 15.4
76
BARTON ON Q - SYSTEM 77
.
830
I
o
o.
. l'....
z i
o ....,
cO
.....
", ,
o
.--
Jy
eo
E ..:
17, z ,
-.
- 9
..
O
.".
825
4.4ir
. . + ...,
0'.
o
.
..
...
ri0 0
o
...
S 5cm
PI
I. ;
o -H
.0
,-. . -
ntictine
ritlip
e0,1041. -r4 (0.1 401,111.
..,411,0,
4 40
'c'
l
.
8 1,51C/C)
1441%
1080-
. V..
815
810
10cm
11111111111111
-I-
;- ..2
.." ......
,..
SIm 1
11111114
,.. ..,...
820
A40
,-,-,44
r.v
iv
4a
(clay sample
(C/C I . ,
7 '``.
L.4
. '..,
+ Simi,
10cm ..' ,
to in- ,.. .
vert
,i,
60
or
or
,---
I'.
ti,
IIt
I
,
KS
4,100
Slmr)
15cm
1070-
a1,
,. . ,
.
S Im I
1111.
1
a.,
10cm
!.
1060
e-,... o
o ,, - c-..1,,,,,,
:
.2 . ,?, I - ' -
805
t..a ,;!.!
). ,-n
lf,
z
.4 ,
Z
1
ice
,1 .
.
.k
'C
,_o
,;
ng
ROCK MASS
-It
TEMPORARY
DESCRIPTION
`I
SUPPORT
SUPPORT
;
= 6
'-' --'
ROCK
NOTES
Gneiss
810 - 817
TUNNEL
crushed
Orginally
Crushed
waterie akage
zone with clay
MAPPING - SUPPORT
LOCALITY
HYLLEN ,
ULLA - FORRE
Lo aN,,
-L'--, I
i
,.-_-,-sr
z ."
z
i,='n
7(
2
NOTES- 1060-1075 Fault 20 cm
.T., 2, a -' a ET. with 10 cm clay filling
with
large
1050 -
111
Lz'e
.,
L---"
.. r/ t' '-'"
zt
, \ , _r
l,c,5
t,x- ROCK MASS ic TEMPORARY
, r
SUPPORT
DESCRIPTION ":
RECOMMENDED
1. L3
Z ,
c
,5', -_-1
C3 --n
- -.
w
C C"'
1080
ROCK
SiON
oar[
25 3 SO et)
PROJEC T
71610
NO
5NEE T NO
TUNNEL
1090
1100
' -_C-%
.
RECOMMENDED
SUPPORT
crushed
clay fitting
MAPPING - SUPPORT
LOCALITY
HOL ME N
(right
s2,
A TI 80
PROJECT
NO
50000
NO
716 28
NO
ROCK MASS
Discontinuity,
thickness 50cm
Crushed zone,
without clay
80
SUPPORT
B L0 o fi Expansion bolts
Crushed zone,
weathered with
clay
Grouted bolts
Strike/dip
Shotcrete
S (mr) , ;
Mesh reinforced
shotcrete with grouted bolts
Cast concrete arch
FIG. 3aExample of tunnel mapping using the Q-system: 160 m 2 headrace tunnel.
FIG. 3bExample of tunnel mapping using the Q-system: 3.3 m diameter TBM driven sewage tunnel.
BARTON ON 0-SYSTEM 79
60 m
40m
40m
1-5
5-10
10-15
15-20
(m)
20-30
30-100
==n==r-)==r-)==n
BO
20m
1.0
'At
--116m
60
U.
0
FIG. 4Vertical section through the VEAS sewage treatment plant, Oslofjord.
CO
SRF
in multiple arch and wall drifts. The predominant form of support in the case records was rockbolts,
or combinations of rockbolts and shotcrete, often mesh reinforced. Occasionally, extreme conditions
called for extreme varieties of support (e.g., 9.8 m long rockbolts on 0.9 m centers together with
14.6 m long bolts on overlapped 0.9 m centers) and mesh-reinforced gunite.
Dimensions
The cases studied ranged from unsupported 1.2 m wide pilot tunnels to unsupported 100 m
wide mine caverns (Fig. 5). The predominant tunnel dimensions (span or diameter) were 5 to 10
m (78 cases) and 10 to 15 m (59 cases). Excavation heights ranged from extreme values of 1.8
to 100 m. A significant body of the case records came from hydroelectric projects; consequently
there were some 40 cases of large caverns with spans in the range of 15 to 30 m and wall heights
in the range of 30 to 60 m.
Depths
Excavation depths ranged from 5 to 2500 m, though most were commonly in the range of 50
to 250 m. The Scandinavian bias caused predominantly by Cecil's (1970) case records is shown
in Fig. 6. Note that the other case records contribute most of the data on the deeper-seated
excavations, including numerous hydropower caverns.
RQD
Support Method
The large majority (180) of the 212 case records were supported excavations. Only 32 cases
were permanently unsupported. Support ranged from spot bolting (as little as 50 bolts over a roof
area of 6000 m 2 ) to very heavy rib-and-rock-bolt-reinforced concrete of 2 to 3 m thickness, poured
The number of joint sets was most commonly in the range of one set (plus random) to three
sets (plus random). Fifty-two (52) cases, the largest group, had exactly three joint sets. Extreme
cases consisted of massive, unjointed rock and completely crushed, disintegrated rock.
The "rock quality designation" (RQD) ranged in a quite uniform manner from 0 up to 100%.
Forty (40) cases lay in the "very poor" category (0 to 25%) and fifty-three (53) cases in the
"excellent" category (90 to 100%).
80
BARTON ON Q-SYSTEM
81
O f /ac RATIO
(STRESS /STRENGTH)
501-
-10
10 -
..
..
HEAVY
ROCK
BURST
10
6-10
16 -
30
20
2.6-6.0
MILD
ROCK
BURST
HIGH
STRESS
MEDIUM
STRESS
0
SCANDINAVIAN CASES (CECIL. 1970)
ME
OTHER CASES
FIG. 6Histogram of tunnel depths.
The stress reduction factor has sixteen (16) classes. These are divided into four broad groups:
(a) weakness zones causing loosening or fall-out, (b) rock stress problems in competent rock, (c)
squeezing (flow of incompetent rock), and (d) swelling (chemical effect due to water uptake).
Seventy-three (73) cases fell in group (a) in which clay fillings were the direct cause of loosening
and fall-out. This can be compared with the statistic for J, in which eighty-one (81) cases were
identified as having "mineral coatings, thin clay fillings," or "thick clay fillings, swelling clay."
In other words, the majority of cases with these features were classed as "weakness zones causing
loosening or fall-out . "
Eighty-one (81) cases were classified as having moderate stress in essentially competent rock;
i.e., with ur ic', (unconfined compression strength/major principal stress) in the moderate range of
10 to 200, which is neither too high nor too low.
Thirty-two (32) cases were classified as having rock stress problems (group (b)) with ratios of
cr,lcr, less than 10. This statistic is shown in Fig. 7. The data for this histogram were obtained
from the case records in which stress and strength data were specifically described. Eleven (II)
of the cases were found to have satisfactory ratios of cr,kr, (i.e., > 10).
The mean and extreme values of the a,./cr, data plotted in Fig. 7 can be summarized by the
following values:
(range) = 1.0 to 62
(It should be noted that several of the case records with et, and a data gave ranges for at least
one of these parameters (e.g., a. equal to 120 to 200 MPa). These ranges, and their extreme value
ratios, were plotted in Fig. 7. The actual case records describing high stress, slabbing, or rock
burst problems numbered only twenty (20). Use of the extreme values expanded this data base to
the 32 cases with a,/a,
10 shown in Fig. 7.)
BARTON ON 0-SYSTEM
.01-0.1
0.1-1.0
4
i 00
I. Igneous
30 -
20 -
Basalt
Diabase
Diorite
Granodiorite
Quartzdiorite
Dolerite
Gabbro
Granite
Aplitic Granite
Monzonitic Granite
Quartz Monzonite
Quartz Porphyry
Tuff
EXCEPT.
EXTREM.
VERY
POOR
POOR
POOR
POOR
FAIR
VERY
0000 0000
EXT.
EXC.
GOOD
The predominant rockmass characteristic in the cases with popping, slabbing, or rockbursting
was relatively massive rock, with few joint sets and/or wide joint spacing. The mean RQD for
these cases was 91% (range 70 to 100%), and the mean J, value was 5.0 (two joint setstwo
plus random). Jointing ranged from three widely spaced sets (J = 9) to massive intact rock (J
= 1.0).
Squeezing or swelling problems (groups (c) and (d)) were encountered in only nine of the case
records, although a total of twelve cases were listed as rock containing swelling clay such as
montmorillonite.
Q-Value
The whole spectrum of rock mass qualities exhibited by the case records is shown in Fig. 8.
As expected, the majority of cases (76%) fall in the central categories "very poor" (Q = 0.1 to
1.0), "poor" (Q = I.0 to 4), "fair" (Q = 4 to 10), and "good" (Q = 10 to 40). The whole
spectrum of case records utilized in the Q-system ranges from qualities of 0.001 (extreme squeezing)
to 800 (essentially unjointed, massive rock).
Rock Types
The distribution of rock types represented in the case records can be summarized as follows:
igneous rock (13 types), metamorphic rock (26 types), and sedimentary rock (II types). Table 6
provides a complete breakdown on the rock types and the number of case record occurrences of
each type. The statistics are dominated by granite (48) and gneiss (21). However, there are
significant numbers of case records involving schist (21), quartzite (13), leptite (11), and amphibolite
(8). Sedimentary rocks are relatively poorly represented with only 19 cases.
records.
III. Sedimentary
100-1000
40 -
II. Metamorphic
83
Amphibolite
Chalk
4
2
1
I
Anorthosite (meta-)
Arkose
Arkose (meta-)
Claystone (meta-)
Limestone
I
3
2
1
Marly Limestone
Mudstone
Calcareous Mudstone
1
2
46
I
1
2
2
2
Dolomite
Gneiss
Biotite Gneiss
Granitic Gneiss
Schistose Gneiss
Graywacke
Grecnstone
Schistose meta Graywacke
Quartz Hornblende
Leptite
Marble
Mylonite
Pegmatite
Syenite
Phyllite
Quartzite
Schist
Biotite Schist
Mica Schist
Limestone Schist
Sparag mite
14
1
4
2
Sandstone
Shale
Clay Shale
Siltstone
Marl
Opalinus Clay
4
2
2
2
I
4
2
1
1
13
17
1
2
1
2
Conclusions
I. The large number of case records utilized to develop the Q-system ensures that reliable
support recommendations are provided for a very wide range of tunnel sizes, types of excavation,
depths, and rock mass qualities.
Detailed analysis of the case records has revealed the overall distribution of individual rock
mass parameters such as joint roughness, alteration, and stress-strength ratios, so that extreme
value cases can be readily identified.
Squeezing ground is the only class of problems that is inadequately represented in the original
data base. Swelling, slabbing, and rock bursting problems are represented in a sufficient number
of case records for reliable determination of support requirements. General tunneling conditions
are extremely well represented, with 160 case records in the range of Q-values from 0.1 (very
poor) to 40 (good).
Fifty individual rock types are represented in the case records. Their characteristics are
quantified in such a manner that the individuality exhibited by many rock types is carried all the
way through to support selection. Application of the Q-system to other rock types than those
described in the case records can be performed with confidence, provided that any special
characteristics of the new rock type are adequately represented in the six parameters. A case in
point would be the susceptibility to alteration by exposure to moisture. The environment expected
under tunnel use must always be carefully considered.
The Q-system has been used for several years in conjunction with Norwegian tunnels
supported with fiber-reinforced microsilica shotcrete, a revolutionary new material that is rapidly
replacing labor-intensive mesh-reinforced shotcrete. Very poor rock qualities previously requiring
DISCUSSION ON Q-SYSTEM 85
DISCUSSION
H. A. D. Kirsten' (written discussion)The table of Barton et al [DI, Table 2] for the joint
alteration number (.10) is quite complex and relatively open to interpretation. The criteria may be
systematized and extended as shown in Table D-1 to overcome these problems to a large extent.
The stress reduction factor (SRF) is not a geological property that varies for different regimes
of rock around an excavation. It is a parameter that characterizes the loosening of the rock around
the excavation as a whole.
Barton et al provide qualitative criteria for determining SRF for incompetent, non-homogeneous
rockmasses [DI, Table 3a1 and competent, homogeneous rockmasses [Dl, Tables 3b, 3c, and
34 The non-homogeneities provided for involve single or multiple clay filled weakness or clay
free shear zones. The determination of SRF is open to interpretation, because of the qualitative
nature of the criteria and the difficulties that often arise in deciding whether the rockmass is
homogeneous or not. Further difficulties arise in the case of homogeneous rockmasses with regard
to assessing the degree of stressing, bursting, squeezing, and swelling.
These problems can be overcome by observing that, in the case of non-homogeneous rock, SRF
is related to the overall quality of the rock, Q, and, in the case of homogeneous rock, to the field
stress state relative to the rockmass strength. The respective relationships are given by the
expressions
Less than
1.0 mm"
mmb
Larger than
5.0 mm
0.75
1.0
2.0
4.0
6.0
3.0
3.0'
6.0'
6.
10.0'
10.0
4.0
8.0'
13.0'
4.0'
8.0
13.0
5.0'
10.0
18.0
DISCUSSION ON Q-SYSTEM 87
. J w
z'
0.00/
0.006
MILD
HEAVY
ROCK BURST ROCK BURST
SQUEEZING SOUSE ZING
SWELLING
SWELLING
1,0
`o
/00
F4
0
c r4
o
R2
Cl...se 2
E0 ..1?':_.0
PcPe
.00e.0%
ei)11,7C
illi
(ROD/JII)(Jr /Jo)
41.,,Z,o
IP0/ 6.4
/.0
0,,,
099
,,,, , .C15'
E
,../0
1111111
IEEE".
TN.,n5'
*
-
Ci CECIL
i
$:
.3-.0
r'ili)
....-:
1. 0.48
SRF
Contours of ---1
n
in
f n r n
E
o
0 .7,
0 k
potential
1,0
( H / UCS)
0,0/
0.176(UCS/H)'
413
where
Q = (RQD/J)(J,JJ)(J/SRF),
maximum-to-minimum principal field stress ratio,
K
H = head of rock corresponding to maximum principal field stress, m, and
UCS = unconfined compressive strength of rock, MPa.
The corresponding rockmass indices are given by the expressions
II
rock)
liMill
00
POOR
=lin
V
RY
GOOD
40 /00
GOOD
1111
XC
GOOD
400 1000
increasing
increasing
loosening -.1,-4.--e-bursting
potential
.- 0
C C el
29
rErt
a)
(after Barton et d Mt I
SELF SUPPORTED CASES
(otter Barton et al (I))
R
POOR
POOR
ii X
0./
13P
Lt
vo
iC>
t
le
g22/ TEFCAGHI
I II IllibrAlill
l ... fratOMIMM
11111111111
(after Barton et al (1)) 111MMIIIII=11111
ormdleiliiiikin_
irE
+ BA RTON TABLE 3(al ii
ii
...J.., to Kirsten)l
. imam,
VO
?iii
II
11111aN=1
Il
roil
,...:
1
........
l' III
n10=113= 6,e
IIIIMIIIIMnleMMMINMENOIN=MO
MMENEW
..
M
11111111111=11011LBINIIMINIMINIIMI
5 MEM Illiek
--4111
CM III
II IIIIMMOMMI
__ mo o IN alimmo mmiumnImlommmannsm
nNMI.
1
211112INIMEIMIIELEINIMI
G END:
AtIks
/,
0,
NO
FRACTURING
SQUEEZING
SWELLING
III
:"." 4' Z
-) S ;
0/
/0
IIIIII11111.1n1111111111
Contours of SRF
,..,/-- for P h / Q n .-1.0
/Op
05
MINIMAL
FRACTURING
SQUEEZING
SWELLING
The ruling value for Q may be determined by calculation as the minimum of these two
expressions. The corresponding value for SRF may also be determined. In the event of this value
corresponding to SRF h it may further be established which of the two terms in the expression for
SRFh is the larger. These two terms represent respectively the stress and structurally controlled
behavior of competent rock.
The proposed procedure for determining SRF replaces that given by Barton et al IDI] and is
illustrated graphically in Fig. D-1 for K = 1.0 and J,. = 1.0. The significance of the proposed
alternative procedure is illustrated in Fig. D-2. The straight-line graph corresponding to SRF =
1.809 Q-" 9 represents the squeezing behavior associated with shear or weakness zones in
incompetent ground. As such it represents the lower bound values for SRF. The domain above
the graph represents the loosening behavior of competent rock, to which the expression for SRF
in terms of K, H, and UCS applies.
The various case histories shown plotted in Fig. D-2 confirm the proposed alternative determination
of SRF. The correspondence between Barton's and Terzaghi's implied relationships between SRF
and Q for incompetent ground is remarkable. The fact that Terzaghi worked in tunnels which were
generally of a squeezing nature and not self-supporting is confirmed in Fig. D-2. It is also evident
that tunnels in ground in which the loosening behavior is governed by shear or weakness zones
or by compressible gouge on the joints are generally not self-supporting.
The behavioral characteristics of the ground surrounding a tunnel are detailed in Table D-2.
The proposed direct calculation of SRF from a limited number of geological parameters is the
only quantification of the loosening potential or stress relaxational behavior of tunnelled ground
available to date. Barton and his co-authors should be congratulated for this contribution, although
they were not explicitly aware of the quantitative implications of their findings.
Controlling
Criterion
Stress in respect of
competent
rock/Shear
or weakness
zones in respect of incompetent
ground
Stress
Reduction
Factor
Probable
Rock Mass
Quality
(SRF)
(0
Excavation-Nature of
Induced
GroundGround
Supporting
Displacement
Action
Indefinite creep
Visco-plastic
arch
0.006-50/
0.006-0.05
Mild rock-bursting,
squeezing, or
swelling
2.5-5
0.05-100/
0.05-0.4
Minimal fracturing,
squeezing, or
swelling
Highly stressed
elastic arch
0.4-2.5
0.4-640/
0.4-100
No facturing,
squeezing, or
swelling
Moderate elastic
deformation
Moderately
stressed elastic
arch
0.4I
6.0-640
No fracturing,
squeezing, or
swelling
Limited elastic
deformation
Lowly stressed
elastic arch
0.4-250
No fracturing,
squeezing, or
swelling
Random block
displacement
Lowly stressed
elastic arch
2.5-5
0.05-10()
No fracturing,
squeezing, or
swelling
Random block
displacement
Keystone arching
by mechanical
interlocking of
blocks
Larger than 5
0.001-50
No fracturing,
squeezing, or
swelling
5-10
1-2.5
Geological
structure in
respect of
competent
rock
ExcavationInduced
Ground
Condition
Discussion References
[DI] Barton, N., Lien, R., and Lunde, J., "Engineering Classification of Rock Masses for the Design of
Tunnel Support," Rock Mechanics, Vol. 6, No. 4, 1974, pp. 189-236.