Rock bolting effect of standard support patterns of Japan Road Association, Japan Highway Public Corporation and Japanese National Railways in various ground conditions are analyzed quantitatively based on the interaction model of rock bolt and rock mass. Shortcrete plays an important effect in the reinforcing system and it works together with rock bolt. Rock bolting effect is improved by thicker shotcrete application in poor ground conditions but its effect is not significant in good ground condition. Rock bolt reinforcement is influenced by the shotcrete and the ground competency factor. Comparisons of the results show that the different standard support patterns do not vary significantly except some differences in rock bolt density parameters and its length. Support performances of all the standard support patterns show the agreement with design recommendation.
4. TTTThhhheeeeoooorrrreeeettttiiiiccccaaaallll bbbbaaaassssiiiissss ooooffff tttthhhheeee ssssttttuuuuddddyyyy
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((MMoohhrr-CCoouulloommbb tthheeoorryy))
SSttrraaiinn ssoofftteenn mmooddeell,,
ddiillaattiioonn
IInntteerraaccttiioonn bbeehhaavviioorr ooff rroocckk
mmaassss aanndd rroocckk bboolltt::
((CCoouupplliinngg aanndd
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bbeehhaavviioorr))
w
o
symmetric
O ra Rf Re
Po
Lz
LT
LT
r L1
Plastic flow
zone
Soften zone
Elastic zone
r
g r o u n d
d i s t r i b u t i o n o f a x i a l f o r c e
t u n n e l P m a x
o p e n i n g
r o c k b o l t
Neutral point
5. Ranges of RRRaaannngggeeesss ooofff ddddeeeeffffoooorrrrmmmmaaaattttiiiioooonnnn mmmmoooodddduuuulllluuuussss
Japan J apa n Ro Road ad As s o c ia Association
t io n
classes mass Japan J apa nHighway Highway Pu blic Co rpo P.
ra t io n
Corp.
Rock Japanese J apa n e s e National Na t io n a l Ra ilways
Railways
0 1000 2000
3000 Deformation modulus (MPa) 500 1000 1500 2000 2500 3000
B
CI
CII
DI
DII
B
CI
CII
DI
DII
III N
II N
I N
I S
I L
Ro c k ma s s c la s s
De f o rma t io n mo du lu s Em (GPa )
6. Study parameters SSStttuuudddyyy pppaaarrraaammmeeettteeerrrsss aaaannnndddd ccccaaaasssseeee aaaarrrrrrrraaaannnnggggeeeemmmmeeeennnnttttssss
β= 0 ~ 1.0
Em = deformation modulus of
rock mass
σc = axial strength
Srp = Competency factor
(=σc/γH)
γ = density of rock
H = overburden depth
β = rock bolt density parameter
(1 = 50×50 cm)
Em=200σc
Srp = 0.1 ~
2.0
2 / b a z t b = p r l r L L
ra=tunnel radius, rb=radius of rock bolt , λ is friction
coefficient Lz and Lt are rock bolt spacing.
7. Study Parameters o SSStttuuudddyyy PPPaaarrraaammmeeettteeerrrsss oooffff JJJJaaaappppaaaannnn RRRRooooaaaadddd AAAAssssssssoooocccciiiiaaaattttiiiioooonnnn
(a) Tunnel radius = 6.25 m ( 4.25 ~ 6.25 m)
Support
pattern no
t'c
(m)
L β z L (m) t Support L (m) (m)
class
Rock
class
B B 3 1.5 2 0.094 0.05 JA1-Pt1
C 3 1.5 1.5 0.128 0.1 JA1-Pt2 I CI
C 3 1.5 1.2 0.16 0.1 JA1-Pt3 II ーa CII
C 3 1.5 1.2 0.16 0.15 JA1-Pt4 II-b
D 3 1.2 1 0.236 0.21 JA1-Pt5 I-a DI
D 4 1.2 1 0.21 JA1-Pt6 I-b
D 4 1.2 <1.0 >0.236 >0.28 JA1-Pt7 II DII
8. Study Parameters SSStttuuudddyyy PPPaaarrraaammmeeettteeerrrsss ooooffff JJJJaaaappppaaaannnn HHHHiiiigggghhhhwwwwaaaayyyy PPPP.... CCCCoooorrrrpppp....
Tunnel radius = 5.1 m
Support
pattern no t'c β (m)
Lz
(m)
Lt Support L (m) (m)
class
Rock
class
B B-a 3 1.5 2 0.094 0.05 JH-Pt1
C 3 1.5 1.5 0.128 0.1 JH-Pt2 I CI
C 3 1.5 1.2 0.16 0.1 JH-Pt3 II ーa CII
C 3 1.2 1.2 0.2 0.15 JH-Pt4 II-b
D 3 1.2 1 0.24 0.21 JH-Pt5 I-a DI
D 4 1.2 1 0.24 0.21 JH-Pt6 I-b
D 4 1.2 <1.0 >0.24 >0.28 JH-Pt7 II DII
9. Study Parameters SSStttuuudddyyy PPPaaarrraaammmeeettteeerrrsss ooooffff JJJJaaaappppaaaannnn NNNNaaaattttiiiioooonnnnaaaallll RRRRaaaaiiiillllwwwwaaaayyyyssss
Support
pattern no t'c L β (m) z L (m) t Support L (m) (m)
class
III 2 3.9 1.5 0.052 0.1 JR1-Pt1 N
II 3 3 1.5 0.068 0.1 JR1-Pt2 N
I 3 1.9 1 0.163 0.21 JR1-Pt3 N
I 3 1.2 1 0.258 0.25 JR1-Pt4 S
I 4 1.2 1 0.258 0.25 JR1-Pt5 S
I 3 2.3 1 0.134 0.28 JR1-Pt6 L
III 2 3 1.5 0.068 0.1 JR2-Pt1 N
II 3 2.3 1.5 0.089 0.1 JR2-Pt2 N
I 3 1.6 1 0.193 0.21 JR2-Pt3 N
I 3 1.1 1 0.281 0.25 JR2-Pt4 S
I 4 1.1 1 0.281 0.25 JR2-Pt5 S
I 3 1.9 1 0.163 0.28 JR2-Pt6 L
10. IIIInnnnfffflllluuuueeeennnncccceeee ooooffff sssshhhhoooottttccccrrrreeeetttteeee tttthhhhiiiicccckkkknnnneeeessssssss
JA1-Pt1: t'c = 0.05 m
and L=3.0 m
JA1-Pt2: t'c = 0.1 m
and L=3.0 m
0.25
0.2
0.15
0.1
0.05
0
0 0.2 0.4 0.6 0.8 1
De s ns it y o f ro c k bo lt β
St ra in (Ura/ ra )
Srp=0.1
Srp=0.1~1.2
0.25
0.2
0.15
0.1
0.05
0
0 0.2 0.4 0.6 0.8 1
De s n s it y o f ro c k bo lt (β )
St ra in (Ura/ ra )
Srp=0.1
Srp=0.1~1.2
11. IIIInnnnfffflllluuuueeeennnncccceeee ooooffff RRRRoooocccckkkk bbbboooolllltttt lllleeeennnnggggtttthhhh
JA1-Pt5: rraa ==66..2255 mm,
tt''cc == 00..2211 mm and
LL==33..00 mm
Em=0~600 MPa
JA1-Pt6: rraa ==66..2255 mm,,
tt''cc == 00..2211 mm and
LL==44..00 mm
0.1
0.08
0.06
0.04
0.02
0.1
0.08
0.06
0.04
0.02
0
0 0.2 0.4 0.6 0.8 1
De n s it y o f ro c k bo lt β
St ra in Ura/ ra
Srp=0.1
Srp=0.1~1.2
0
0 0.2 0.4 0.6 0.8 1
De n s it y o f ro c k bo lt β
St ra in Ura/ ra
00..2244
Srp=0.1
Srp=0.1~1.2
12. Comparison of tunnel CCCooommmpppaaarrriiisssooonnn ooofff tttuuunnnnnneeelll wwwwaaaallllllll ddddiiiissssppppllllaaaacccceeeemmmmeeeennnntttt
350
300
250
200
150
100
50
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 .1 1.2
Comp e t e nc y fa c t or (Srp )
Dis p la c e me nt (c m)
St an da rd Su ppo rt (J A1 - Pt7)
No s uppo rt
50
45
Dis pa lc e me nt (c m) St an da rd Su ppo rt (J A1 - Pt7)
40
35
30
25
20
15
10
5
0
Sh o rt c re t e o n ly
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 .1 1 .2
Comp e t e nc y fa c to r (Srp)
DDiissppllaacceemmeenntt
rreessttrraaiinneedd bbyy
rroocckk bboolltt
13. IIIInnnnfffflllluuuueeeennnncccceeee ooooffff RRRRoooocccckkkk bbbboooolllltttt lllleeeennnnggggtttthhhh
JH-Pt5: rraa ==55..11 mm,
tt''cc == 00..2211 mm and
LL==33..00 mm
JH-Pt6: rraa ==55..11 mm,
tt''cc == 00..2211 mm and
LL==44..00 mm
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Srp=0.1
0 0.2 0.4 0.6 0.8 1
De ns ity o f roc k bo lt β
St ra in (Ura/ ra )
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0 0.2 0.4 0.6 0.8 1
De ns ity of ro c k bo lt β
St ra in (Ura/ ra )
Srp=0.2
Srp=0.1
Srp=0.2
Srp=0.1~1.2
Srp=0.1~1.2
20. FFFFuuuuttttuuuurrrreeee ssssttttuuuuddddyyyy
• Comprehensive verification with measured in-situ
data
• Consider gravity effect and try to include
influence of in-situ stress ratio.
• Study on shallow depth tunnel
Shortcrete works together with rock bolt, and it plays an important effect in the reinforcing system.
Rock bolt effect is significantly improved by shotcrete application in poor ground conditions (Srp&lt;0.4) but its effect is not significant when Srp&gt;0.8.
Increase in rock bolt length up to 6 m, increases the rock bolting effect in weak rock masses when the tunnel radius is large (ra=6.25~7 m) but no difference is seen when the rock bolt is longer than 3 m for medium size tunnel (ra=5.1 m).
Performance of different standard support patterns of JRA, JH and JNR do not vary significantly.
Supporting patterns of JH is almost similar to that of JRA
In a good ground condition, rock bolt density of JR is smaller than that of JH. However there is no significant difference of their reinforcing effect.
In a weak ground condition, rock bolt density of JR is larger than that of JH. The reinforcing effect of the pattern of JR is a little better than that of JH.