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Cost Comparison Case Study in Slope Stabilization using FRP
Reinforced and Soil Nailing in Korea
DAEWON SOIL CO., LTD.CONSTRUCTION & ENGINEERING
CONTENTS
1. Reinforcing Principle and Used Material ············································································· 1
2. Cost Comparison by Slope Stability Analysis ··································································· 1
1) Assumed Ground Condition in Slope Stability Analysis ··························································· 1
2) Modelling of FRP pipe and Assumed Cohesion Increment in Slope
Stability Analysis ···························································································································· 1
3) Assumed Cohesion Increments in Slope Stability Analysis ······················································· 2
4) Case of Soil Slope ·························································································································· 2
(1) Summary of Slope Stability Analysis ····················································································· 2
(2) Spacing and Length of Reinforcing Members Required
to Meet Stability Requirement(Assumed slope length is 100m) ·········································· 3
(3) Summary of Costs in Case of Soil Slope ············································································· 3
(4) Results of the Slope Stability Analysis ·················································································· 4
① Slope Height : 20m ············································································································· 4
② Slope Height : 30m ············································································································· 8
5) Case of Weathered (or Fractured) Rock Slope ········································································· 12
(1) Summary of Slope Stability Analysis ··················································································· 12
(2) Spacing and Length of Reinforcing Members Required
to Meet Stability Requirement(Assumed slope length is 100m) ········································ 13
(3) Summary of Costs in Case of Weathered Rock Slope ······················································ 13
(4) Results of the Slope Stability Analysis ················································································ 14
① Slope Height : 20m ··········································································································· 14
② Slope Height : 30m ··········································································································· 18
3. Summary of Costs in Soil and Weathered Rock Slopes ······································ 22
4. Conclusions ································································································································· 22
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1. Reinforcing Principle and Used Materials
Category Schematic Diagram Materials Remark
FRPReinforced Grouting
▶ All around(360°) Pressure Grouting
- High Strength FRP pipe (Inner Dia. Φ37mm, Thickness 5mm) - Grout : cement + FRC (rapid hardening admixture)
- semi-permanent
durability
- ground improvement
due to pressure grouting
to surrounding soil
- good constructablity
due to lightweight of
the pipe
SoilNailing
▶ Filling Grouting(non-pressure) - Steel Deformed Bar(D29, Dia.29mm)
- Grout : cement
- bad performance due to corrosion, possibility of grout loss in loose or fractured ground, and low strength of re-bar
2. Cost Comparison by Slope Stability Analysis
1) Assumed Ground Conditions in Slope Stability Analysis
Category Soil Slope Weathered Rock Slope
Soil Properties
Unit Weight, γ (tf/m3) 1.9 2.1
Cohesion, c (tf/m2) 2 3
Friction angle, Φ (degree) 30 35
Slope Configuration
Height (m) 20 30 20 30
Length (m) 100 100
Inclination (Ver:Hor) 1:1.2 1:1.0
2) Modelling of FRP pipe and Assumed Cohesion Increment in Slope Stability Analysis
◉ FRP Modelling : nailing effect(FRP pipe) + cohesion increase in ground
◉ Cohesion Increment according to Spacing of FRP pipes
- Case-1 : poor groutability ground with low permeability
- Case-2 : good groutability ground with high permeability
- 2 -
3) Assumed Cohesion Increments in Slope Stability Analysis
Ground
Case-1(poor groutability)
Case-2(good groutability) Friction
Increment(degree)Spacing of FRP
pipes (m)Cohesion
Increment (tf/m2)Spacing of FRP
pipes (m)Cohesion
Increment (tf/m2)
Soil3.0×3.0 1.25 3.0×2.5 1.30 0
1.8×2.0 1.60 2.0×2.0 1.80 0
Weathered Rock
2.5×3.0 1.25 2.6×3.0 1.50 0
2.5×2.0 1.45 2.8×2.0 1.70 0
(Reference : Korean Geotechnical Society, 2000. 9 ; Korea Highway Corporation and
Seoul National University, 2002. 2)
4) Case of Soil Slope
(1) Summary of Slope Stability Analysis
CategoryFactor of Safety
RemarkDry Condition Wet Condition
SlopeHeight:
20m
Non-Reinforced 1.50 0.84
Minimum Required Factor of Safety:
- Dry Condition: 1.5- Wet Condition: 1.2
FRPCase-1 2.00 1.24
Case-2 2.00 1.25
Soil Nail 2.10 1.23
SlopeHeight:
30m
Non-Reinforced 1.39 0.69
FRPCase-1 2.25 1.20
Case-2 2.06 1.20
Soil Nail 2.29 1.24
- 3 -
(2) Spacing and Length of Reinforcing Members Required to Meet Stability Requirement (Assumed slope length is 100m.)
① Slope Height : 20m ② Slope Height : 30m
Category Reinforcing Member
Length (m) Number (ea)
FRP
Case-13.0×2.5
(m)
8 34
10 33
12 67
14 134
Case-23.0×3.0
(m)
8 34
10 33
12 67
14 134
Soil Nail1.5×1.5
(m)
10 134
12 134
14 469
Category Reinforcing MemberLength (m) Number (ea)
FRP
Case-11.8×2.0
(m)
4 5610 5612 16814 11216 16818 11220 336
Case-22.0×2.0
(m)
4 5110 5012 15114 10216 15118 10120 302
Soil Nail1.2×1.2
(m)
10 8412 41714 8416 50120 835
(3) Summary of Costs in Case of Soil Slope(1000 WON = 1 USD)
Category Soil Slope
Slope Height 20m 30m
Cost for FRP
Case-1 338,148 USD 1,627,070 USD
Case-2 338,148 USD 1,464,899 USD
Cost for Soil Nailing 611,055 USD 2,038,308 USD
- 4 -
(4) Results of the Slope Stability Analysis
① Slope Height : 20m
Non-Reinforced (Dry Condition)
Non-Reinforced (Wet Condition)
- 5 -
FRP-Reinforced Case-1 (Dry Condition)
FRP-Reinforced Case-1 (Wet Condition)
- 6 -
FRP-Reinforced Case-2 (Dry Condition)
FRP-Reinforced Case-2 (Wet Condition)
- 7 -
Soil Nail-Reinforced (Dry Condition)
Soil Nail-Reinforced (Wet Condition)
- 8 -
② Slope Height : 30m
Non-Reinforced (Dry Condition)
Non-Reinforced (Wet Condition)
- 9 -
FRP-Reinforced Case-1 (Dry Condition)
FRP-Reinforced Case-1 (Wet Condition)
- 10 -
FRP-Reinforced Case-2 (Dry Condition)
FRP-Reinforced Case-2 (Wet Condition)
- 11 -
Soil Nail-Reinforced (Dry Condition)
Soil Nail-Reinforced (Wet Condition)
- 12 -
5) Case of Weathered (or Fractured) Rock Slope
(1) Summary of Slope Stability Analysis
CategoryFactor of Safety
RemarkDry Condition Wet Condition
SlopeHeight20m
Non-Reinforced 1.72 0.95
Minimum Required Factor of Safety:
- Dry Condition: 1.5- Wet Condition: 1.2
FRPcase-1 2.05 1.20
case-2 2.07 1.22
Soil Nail 2.13 1.22
SlopeHeight30m
Non-Reinforced 1.57 0.81
FRPcase-1 2.09 1.20
case-2 2.09 1.21
Soil Nail 2.24 1.25
- 13 -
(2) Spacing and Length of Reinforcing Members Required to Meet Stability Requirement (Assumed slope length is 100m.)
① Slope Height : 20m ② Slope Height : 30m
Category Reinforcing Member
Length (m) Number (ea)
FRP
case-12.5×3.0
(m)
10 41
12 121
14 41
case-22.5×3.0
(m)
10 41
12 121
14 41
Soil Nail1.5×2.5
(m)
8 67
14 268
16 134
Category Reinforcing MemberLength (m) Number (ea)
FRP
case-12.6×2.0
(m)
6 399 38
12 3914 15316 15518 3820 231
case-22.8×2.0
(m)
6 369 36
12 3614 14416 14418 3620 216
Soil Nail1.5×1.2
(m)
14 20118 40220 469
22 402
(3) Summary of Costs in Weathered Rock Slope
(1000 WON = 1 USD)
Category Weathered Rock Slope
Slope Height 20m 30m
Cost for FRP
case-1 235,742 USD 1,061,614 USD
case-2 235,742 USD 992,904 USD
Cost for Soil Nailing 378,175 USD 1,662,398 USD
- 14 -
(4) Results of the Slope Analysis
① Slope Height : 20m
Non-Reinforced (Dry Condition)
Non-Reinforced (Wet Condition)
- 15 -
FRP-Reinforced Case-1 (Dry Condition)
FRP-Reinforced Case-1 (Wet Condition)
- 16 -
FRP-Reinforced Case-2 (Dry Condition)
FRP-Reinforced Case-1 (Wet Condition)
- 17 -
Soil Nail-Reinforced (Dry Condition)
Soil Nail-Reinforced (Wet Condition)
- 18 -
② Slope Height : 30m
Non-Reinforced (Dry Condition)
Non-Reinforced (Wet Condition)
- 19 -
FRP-Reinforced Case-1 (Dry Condition)
FRP-Reinforced Case-1 (Wet Condition)
- 20 -
FRP-Reinforced Case-2 (Dry Condition)
FRP-Reinforced Case-2 (Wet Condition)
- 21 -
Soil Nail-Reinforced (Dry Condition)
Soil Nail-Reinforced (Wet Condition)
- 22 -
3. Summary of Costs in Soil and Weathered Rock Slopes
(1000 WON = 1 USD)
Category Soil Slope Weathered Rock Slope
Slope Height 20m 30m 20m 30m
Cost for FRP
Case-1 338,148 USD 1,627,070 USD 235,742 USD 1,061,614 USD
Case-2 338,148 USD 1,464,899 USD 235,742 USD 992,904 USD
Cost for Soil Nailing 611,055 USD 2,038,308 USD 378,175 USD 1,662,398 USD
4. Conclusions
1) FRP reinforced grouting method for slope stabilization has been developed to improve some intrinsic shortcomings of the soil-nailing using steel rebar, such as corrosion, heavy weight, difficulty in cutting and low performance.
2) Fiberglass reinforced plastic (FRP) pipe has been also developed as reinforcing member since 1999. Surely new material is highly strong, endurable to corrosion, light in weight, easy to cut, and highly resistable to oxidation, etc.
3) FRP grouting method have two distinct reinforcing effects; the first is arching effect by high strength FRP pipe. The second is cohesion increase of the ground itself by pressure grouting injected inside the FRP pipe with pressure relevant to surrounding ground to fill not only the annulus between the bored hole and FRP pipe but also existing discontinuities surrounding the FRP pipe. The ground will be strengthened due to reinforcement by FRP pipe and improved by pressured grouting. It is, therefore, possible to increase the space between FRP nails, compared to conventional soil nailing method.
4) In this cost comparison between FRP grouting and soil nailing, it was shown that the FRP method in soil and weathered(or fractured) rock slopes has more economic performance than the conventional soil nailing method. The cost estimation for each case is based on design standard of Korea and only applicable to top-down case where neither cranes nor scaffolds is involved. The cost for drainage system, which will be about same for both methods, is also omitted in this case study.
- 23 -
Information on FRP Reinforced Grouting Method
< Reference >
1. Y. K. Choi, 2004, "Longitudinal Arching Effects around a Soil-Tunnel by Face-Reinforcing, PhD Dissertation, University of Konkuk, Seoul, Korea.
2. J. H. Park, 2002, "Effect of Pressure Grouting on Ground Reinforcement" PhD Dissertation, University of Myunggi, Seoul, Korea.
3. J. H. Park, Y. K. Choi, J. D. Lee and G. J. Bae, 2003, "The Case Study on Using FRP Mult-Step Grouting for Reinforciment of Tunnel in Fracture Zone", Proceedings of the ITA world Tunneling Congress, Amsterdam in Netherlands, pp. 573~576.
4. Korean Geotechnical Society, 2000. 9, "Development on FRP Reinforced Grouting Method"
5. Korea Highway Corporation and Seoul National University, 2002. 2, "Development of the Design Methodology of Reinforcement Grouting Using FRP pipe"
6.. O. Y. Kwon, Y. K. Choi, M. R. Oh, S. H. Kim and N. Y. Kim, 2002, "Development and Evaluation of the Applicability for High Strength FRP Pipes as the Grouted-Reinforcing Members in Tunnel", Proceedings of the ITA world Tunneling Congress, Sydney in Australia, Netherlands.
7. S. H. Kim, Y. C. Hwang, N, Y, Kim and Y, K, Choi, 2001, "Reinforcing Method of Rock Slope Using FRP Pipe", International Conference on Landslides", Davos in Switzerland, pp. 535~534.
8. Y. K. Choi, J. H. Park, Y. J. Chung and I. P. Hong, 2004, "Reinforcing Effect of FRP Multi-step Grouting Method for NATM Tunnel by Back Analysis Method", Proceedings of the 30th ITA-AITS world Tunneling Congress, Singapore, pp. 1179~1186.
9. Y. K. Choi, S. B. Woo, O. Y. Kwon, J. H. Park and H. H. Han, 2003, "Shear Strength Characteristics and Behavior of Ground Grouted Using FRP Reinforcing Members", Proceedings of the 12th Asian Regional Conference on Soil Mechanics & Geotechnical Engineering, Singapore, pp. 461~464.