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
1 -
1. Reinforcing Principle and Used Materials Category
Schematic Diagram
Materials
- semi-permanent
- High Strength
▶ All around(360°) Pressure
durability
FRP pipe
Grouting
FRP
Remark
- ground improvement
(Inner Dia. Φ37mm,
Reinforced Grouting
Thickness 5mm)
due to pressure grouting
- Grout :
to surrounding soil
cement + FRC
- good constructablity
(rapid hardening
due to lightweight of
admixture)
▶ Filling Grouting(non-pressure) Soil
the pipe - bad performance
- Steel Deformed
due to corrosion,
Bar(D29, Dia.29mm)
possibility of grout loss in loose or
Nailing
fractured ground, - Grout : cement
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
1.9
2.1
Cohesion, c (tf/m )
2
3
Friction angle, Φ (degree)
30
35
3
Unit Weight, γ (tf/m ) Soil Properties
2
Height (m) Slope Configuration
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 Case-1 (poor groutability)
Case-2 (good groutability)
Ground
Friction Increment
Spacing of FRP Spacing of FRP Cohesion Cohesion (degree) 2 2 pipes (m) pipes (m) Increment (tf/m ) Increment (tf/m ) 3.0×3.0
1.25
3.0×2.5
1.30
0
1.8×2.0
1.60
2.0×2.0
1.80
0
Weathered
2.5×3.0
1.25
2.6×3.0
1.50
0
Rock
2.5×2.0
1.45
2.8×2.0
1.70
0
Soil
(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 Factor of Safety Category Wet Condition
Non-Reinforced
1.50
0.84
Case-1
2.00
1.24
Case-2
2.00
1.25
Slope Height:
Remark Dry Condition
FRP
20m
Minimum Required Soil Nail
2.10
1.23
Factor of Safety:
Non-Reinforced
1.39
0.69
- Dry Condition: 1.5
Case-1
2.25
1.20
Case-2
2.06
1.20
2.29
1.24
- Wet Condition: 1.2 Slope Height: 30m
FRP
Soil Nail
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
Category Length (m)
Case-1
Number (ea)
8
34
10
33
Reinforcing Member Length (m) Number (ea) 4 56
Case-1 1.8×2.0 (m)
3.0×2.5
12
67
14
134
(m) FRP
Case-2
34
10
33
12
67
14
134
10
134
12
134
Soil Nail 1.5×1.5
14
112
16
168
18
112
20
336 51 50
Case-2
12
151
2.0×2.0
14
102
(m)
16
151
18
101
20
302
10
84
Soil Nail
12
417
1.2×1.2
14
84
(m)
16
501
20
835
(m) 14
168
4
3.0×3.0 (m)
56
12
10
FRP 8
10
469
(3) Summary of Costs in Case of Soil Slope (1000 WON = 1 USD)
Category
Soil Slope 20m
30m
Case-1
338,148 USD
1,627,070 USD
Case-2
338,148 USD
1,464,899 USD
611,055 USD
2,038,308 USD
Slope Height
Cost for FRP
Cost for Soil Nailing
4 -
(4) Results of the Slope Stability Analysis
â‘ 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 -
â‘Ą 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
Factor of Safety Category
Remark Dry Condition
Wet Condition
1.72
0.95
case-1
2.05
1.20
case-2
2.07
1.22
Non-Reinforced Slope Height
FRP
20m
Minimum Required Soil Nail
2.13
1.22
Non-Reinforced
1.57
0.81
Factor of Safety: - Dry Condition: 1.5 - Wet Condition: 1.2
Slope Height 30m
case-1
2.09
1.20
case-2
2.09
1.21
2.24
1.25
FRP
Soil Nail
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
Reinforcing Member
Category
Category Length (m)
Number (ea)
10
41
12
121
14
41
10
41
12
121
14
41
8
67
14
268
16
134
case-1
case-1
2.6×2.0
2.5×3.0
(m)
(m) FRP
FRP case-2
case-2
2.5×3.0
2.8×2.0
(m)
(m)
Soil Nail
Soil Nail
1.5×2.5 (m)
1.5×1.2 (m)
Reinforcing Member Length (m) Number (ea) 6 39 9 38 12 39 14 153 16 155 18 38 20 231 6 36 9 36 12 36 14 144 16 144 18 36 20 216 14 201 18 402 20 469 22
402
(3) Summary of Costs in Weathered Rock Slope (1000 WON = 1 USD)
Category
Weathered Rock Slope
Slope Height
20m
30m
case-1
235,742 USD
1,061,614 USD
case-2
235,742 USD
992,904 USD
378,175 USD
1,662,398 USD
Cost for FRP
Cost for Soil Nailing
14 -
(4) Results of the Slope Analysis
â‘ 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 -
â‘Ą 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
Slope Height Cost for FRP
Weathered Rock Slope
20m
30m
20m
30m
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
611,055 USD
2,038,308 USD
378,175 USD
1,662,398 USD
Cost for Soil Nailing
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.
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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.
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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.
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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.
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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.
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