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

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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

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(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

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(4) Results of the Slope Stability Analysis

① Slope Height : 20m

Non-Reinforced (Dry Condition)

Non-Reinforced (Wet Condition)

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FRP-Reinforced Case-1 (Dry Condition)

FRP-Reinforced Case-1 (Wet Condition)

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FRP-Reinforced Case-2 (Dry Condition)

FRP-Reinforced Case-2 (Wet Condition)

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Soil Nail-Reinforced (Dry Condition)

Soil Nail-Reinforced (Wet Condition)

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② Slope Height : 30m

Non-Reinforced (Dry Condition)

Non-Reinforced (Wet Condition)

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FRP-Reinforced Case-1 (Dry Condition)

FRP-Reinforced Case-1 (Wet Condition)

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FRP-Reinforced Case-2 (Dry Condition)

FRP-Reinforced Case-2 (Wet Condition)

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Soil Nail-Reinforced (Dry Condition)

Soil Nail-Reinforced (Wet Condition)

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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

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(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

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(4) Results of the Slope Analysis

① Slope Height : 20m

Non-Reinforced (Dry Condition)

Non-Reinforced (Wet Condition)

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FRP-Reinforced Case-1 (Dry Condition)

FRP-Reinforced Case-1 (Wet Condition)

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FRP-Reinforced Case-2 (Dry Condition)

FRP-Reinforced Case-1 (Wet Condition)

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Soil Nail-Reinforced (Dry Condition)

Soil Nail-Reinforced (Wet Condition)

- 18 -

② Slope Height : 30m

Non-Reinforced (Dry Condition)

Non-Reinforced (Wet Condition)

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FRP-Reinforced Case-1 (Dry Condition)

FRP-Reinforced Case-1 (Wet Condition)

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FRP-Reinforced Case-2 (Dry Condition)

FRP-Reinforced Case-2 (Wet Condition)

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Soil Nail-Reinforced (Dry Condition)

Soil Nail-Reinforced (Wet Condition)

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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.

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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.

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.