Information on FRP Reinforced Grouting Method

DAEWON CO., LTD. CONSTRUCTION & ENGINEERING

1 CONTENTS

1. Back Ground of Development ······································································ 1

2. FRP Reinforced Grouting Method ······························································ 1

2.1 Concept of FRP Reinforced Grouting Method ························································· 1

2.2 Construction Sequence ····························································································· 2

3. Detailed Method Statement ········································································· 8

3.1 Introduction ·············································································································· 8

3.2 Increment against Distance by Pressure Grouting ··································· 9

3.3 Application Example on Imaginary Slope ······························································· 13

3.4 Soil Strength Increment against FRP Nail Space ····················································· 15

4. Material Specification ·················································································· 17 4.1 FRP Pipe ··················································································································· 17

4.2 Coupler ····················································································································· 18 4.3 Caulking Material ····································································································· 19

4.4 Sealing Material ······································································································· 19

4.5 Injecting Material (High strength grouting) ····························································· 19

4.6 Cap Plate and Nut ····································································································· 20

5. Experiment on FRP Pipes ··········································································· 20 5.1 Tensile Strength ········································································································ 20

5.2 ·········································································································· 20

5.3 Summary of FRP Pipe Properties ············································································· 21

6. Laboratory Pullout Test for Bond Experiment on FRP Pipes ················· 21

6.1 Purpose of Experiment ····························································································· 21

6.2 Test Method ·············································································································· 24 6.3 Test Results and Discussion ························································································ 24

7. In Situ Testing ······························································································ 26

7.1 Pressuremeter Testing ······························································································ 26

7.1 Shear Tests ································································································ 27

2 Information on FRP Reinforced Grouting Method

1. Back Ground of Development Various reinforcing methods such as , micro pile, rock bolt, RPUM (Reinforced Protective Umbrella Method), etc. are applied to the slopes and constructed in incompetent ground. The reinforcement members used in reinforcing methods to stabilize the slopes and tunnels have been mainly made of steel.

a) Soil Nailing Method and Ground Anchor for slope b) Rock Bolt in NATM for Figure 1.1 Various Reinforcing Methods

When the steel is used as reinforcement there are some intrinsic problems of steel such as corrosion, heavy weight, and difficulty in cutting: Corrosion ratio of steel inside is usually 1mm/year, but sometimes it is over 10mm/year. The weight of steel reinforcement is normally 3 ~ 6 kg/m and length of reinforcement is usually more than 6m. Therefore the needs for new materials substituting the steel reinforcements arise. Surely the new materials should be endurable to corrosion, light in weight, easy to , and strong enough to replace steel. Glass fiber reinforced plastic (FRP) pipe was developed as reinforcing member in Korea 5 years ago and has been widely used in stabilizing slopes and tunnels because of its advantages: light weight(about 1/3 compared to steel), high resistance to oxidation, high tensile strength, etc.

2. FRP Reinforced Grouting Method 2.1 Concept of FRP Reinforced Grouting Method In loose/colluvial or highly fractured rocks, the arching effect between reinforcements is not guaranteed unless the space between reinforcements is small enough. Grouting with pressure of about 5kgf/cm2 usually, therefore, is needed to ensure the stability of ground between reinforcements in that case. There can be two ways we can think of: 1) reducing of space between reinforcements, 2) improving the ground between the reinforcements. In this case it will be more economical to improve ground itself instead of reducing the space between reinforcements. That is

3 the reason why the pressure grouting is used. The FRP Reinforced Grouting Method using both FRP pipe as reinforcement and grouting with pressure was developed to stabilize incompetent ground as stated above. The scheme of this method is as follows: After drilling a hole in the ground, the high strength FRP pipe is inserted through the hole. Then high strength (FRC No.1 + Portland cement) is injected inside the FRP pipe with some pressure relevant to surrounding ground to fill not only the annulus between the bored hole and FRP pipe but also any existing discontinuities surrounding the FRP pipe. The ground, therefore, will be strengthened due to reinforcement by FRP pipe and improvement by pressured grouting.

2.2 Construction Sequence Construction sequence of FRP Reinforced Grouting Method consists of four steps. Followings are the details of each step:

1st Step: Drilling

A hole with usual diameter over than 105mm is drilled by drilling machine.

Drilled Hole

Drilled Diameter : over O105mm Length of drilled : over 4.000~12.000

Figure 2.1 Drilling

4 2nd Step: Installation of FRP pipe

The FRP pipe with sealing hose are inserted into the hole.

Hose for Sealing admixture discharge

FRP pipe Drilling Hole

Hose for sealing admixture injection Spacer

FRP specification : Special manufactured fiber reinforced plastic -Inner diameter : over than O37m/m -Thickness : over than 5.0m/m FRP Length : over than 4.000m Connection uses special manufactured coupler.

Figure 2.2 Installation of FRP pipe

5 3nd Step: Entrance caulking outside the FRP pipe in the hole

The FRP pipe and sealing hose are inserted into the hole. Then the entrance of drilled hole is caulked for the annulus between drilled hole and FRP pipe to be filled by sealing admixture to be injected through the sealing hose.

Hose for Sealing admixture discharge

Caulking FRP pipe Drilled Hole

Hose for sealing admixture injection Spacer

Caulking between FRP pipe and drilled hole (Perform more than 30㎝ from entrance of drilled hole) caulking material : CEROMAX CX-1 or blowing urethan caulking material must endure over maximum pressure 40kg/cm2

Figure 2.3 Entrance caulking outside of FRP pipe in the hole

6

4rd Step: Sealing throughout the hole outside the FRP pipe

Sealing admixture is injected through sealing hose to fill the annulus between drilled hole and FRP pipe. The purpose of sealing is to prevent the grout materials from flowing toward the entrance of the hole during the further pressure grouting.

Discharge hose for Sealing admixture

Caulking FRP pipe Sealing material Drilling Hole

Injection hose for sealing admixture spacer Use sealing material manufactured specially injection by pressrue in the range 1~3step(1~2kg/cm )2 remove injection hose after sealing

Injection plant

Figure 2.4 Sealing throughout the hole outside of FRP pipe

7 5th Step: Grouting through small holes of the pipe by packer

Grouting is then injected inside the FRP with some pressure relevant to surrounding ground by injection air packer system through the pipe..

a) Inserting the packer into the pipe b) Pressure grouting by the packer from tip

of the pipe to the entrance

injected the gro FRP pipe Packer Caulking Drilling Hole Sealed

A liquid B liquid(1.5 SHOT)

spacer

Use AIR Packer System that the length of rubber is more th Inject high-strength the grout(FRC No.1+Cement) and the rapid hardening admixture simultaneously. Injection Pressure : P = 5~15kg/cm,2 ΔP = 1~10kg/m 2 Injection plant according to field and geologic condition.

Figure 2.5 Grouting through small holes of the pipe by packer

8 6th Step: Installing bearing plate

Finally bearing plate is installed for union between FRP pipe and the ground. The size of bearing plate is usually for union 200mm×200mm×9mm. According to the field conditions, the plate can be omitted.

Bearing plate FRP pipe Drilled Hole injected the gro Caulking Sealed

nut

spacer

Figure 2.6 Installing bearing plate

9 3. Detailed Method Statement 3.1 Introduction The increasing effect of grouting in loose soils or highly weathered rocks will be different from that effect of grouting in rocks. The pressure grouting will not only improve the ground itself but also increase the force between reinforcement and ground. Also the diameter of drilled hole will increase due to pressure grouting. Effective injection area by pressure grouting can be estimated by equation normally used in other injection method, but the exact estimation of injection area will not be easy due to non-homogeneous and anisotropic characteristics of ground itself, various type injection material, and different types of injection method. Especially the reinforcing effect of grouting in rocks will be varied depending upon various factors such spaces and length of discontinuity, the characteristics of material in discontinuity, etc. Therefore the determination of general design criteria for grouting effect will not be easy. In this presentation the design methodology of grouting effect in loose soils and highly weathered rocks will be presented.

The detailed procedure of design method will be as follows:

Step 1: Design of Nailing in given slope - Reinforcement: FRP - Diameter of drilled hole: 105mm - Determination of layout and length of reinforcement satisfying allowable factor of safety

Step 2: Estimation of cohesion increment - to estimate cohesion increment using Figure 5.13 - the inclination angle and original value of cohesion will affect the amount of cohesion increment

Step 3: Re-design using estimated cohesion increase - design will be terminated if the space between nails satisfying required minimum safety factor is below the limit suggested in Figure 3.1 - estimation of cohesion increment and space will be repeated if space between nails is above the limit

10 The outer parabolic solid line in Figure 3.1 can be determined the results of borehole shear test. The limit of space between FRP nails should be determined by ground and site condition, and especially it should be located within the effective grouting area. The increase in friction force and effect of enlargement of drilled hole will not be included in this design method due to not sufficient observed data, but it can be included if further research are carried out in the future.

Figure 3.1 Cohesion Increment vs. Distance from FRP Grouting Hole

3.2 Cohesion Increment against Distance by Pressure Grouting The graph of cohesion increment against distance was developed using both the results of and borehole shear test. TALREN program was used in slope stability analysis. The tensile strength, shear strength, bending stiffness of single reinforcement or combined reinforcements such as anchor, soil nail, micro-pile, , sheet pile, , etc, can be considered in this program. The proposed graph can not be utilized in general manner because it was derived from given specific ground such as Figure 5.14. Therefore more tests on various ground condition should be carried out for the proposed design method to be used in general condition. Figure 3.2 shows the drilling log of test site.

11

Figure 3.2 Borehole Log of Test Site

The height of slope is 15m, slope angle is 1:0.5 and 1:0.7, and space of nails is 1.5m in both slopes for convenience. Both 6m and 8m length of nails are used in research. The slope is composed of single soil and 9 arrows of nails were used. Summary of soil properties are as below:

Table 3.1 Soil and Reinforcement Properties used in Research soil reinforcement unit cohesion friction length Diameter of Nail weight (t/m2) (°) (m) (m) (t/m3) 2.0 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 35 6, 8 0.105

12

(a) 1:0.5 slope (b) 1:0.7 slope Figure 3.3 Section of Slopes used in Research

The change in factor of safety against change in cohesion is shown in Figure 3.4 with several combination of slope angle and nail length. The inclined solid line in Figure 3.4 represents the factor of safety of slope having cohesion of 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 t/m2, respectively with same nail space 1.5m × 1.5m. On the other hand, the five horizontal lines show factor of safety of slope having cohesion of 0.5, 1.0, 2.0, 3.0, and 4.0 t/m2, respectively with same nail space 2.5m×2.5m. Therefore the difference between the original cohesion of ground and value of intersection point between two lines represents required cohesion increment to achieve the same factor of safety.

2.5 2.5 1:0.5, L=6m 기준 1:0.5, L=8m 기준 기준점착력 - 0.5 t/m^2 기준점착력 - 0.5 t/m^2 기준점착력 - 1.0 t/m^2 기준점착력 - 1.0 t/m^2 2.0 기준점착력 - 2.0 t/m^2 2.0 기준점착력 - 2.0 t/m^2 기준점착력 - 3.0 t/m^2 기준점착력 - 3.0 t/m^2 기준점착력 - 4.0 t/m^2 기준점착력 - 4.0 t/m^2 1.5 1.5 안전율 안전율 1.0 1.0

0.5 0.5

0.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 점착력(t/m2) 점착력(t/m2) (a) slope angle=1:0.5, nail length=6m (b) slope angle=1:0.5, nail length=8m 3.0 3.0 1:0.7, L=8m 기준 1:0.7, L=6m 기준 기준점착력 - 0.5 t/m^2 기준점착력 - 0.5 t/m^2 기준점착력 - 1.0 t/m^2 기준점착력 - 1.0 t/m^2 2.5 2.5 기준점착력 - 2.0 t/m^2 기준점착력 - 2.0 t/m^2 기준점착력 - 3.0 t/m^2 기준점착력 - 3.0 t/m^2 기준점착력 - 4.0 t/m^2 기준점착력 - 4.0 t/m^2 2.0 2.0 1.5 1.5 안전율

안전율 1.0 1.0 0.5 0.5 0.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 점착력(t/m2) 점착력(t/m2) (c) slope angle=1:0.7, nail length=6m (d) slope angle=1:0.7, nail length=8m Figure 3.4 Factor of Safety against Cohesion of Original Ground

13 Figure 3.5 shows the required cohesion increment against original cohesion when the nail space changes from 1.5m×1.5m to 2.5m×2.5m. The factor of safety of slope will not change if the nail space changes from 1.5m×1.5m to 2.5m×2.5m where the cohesion increment is 1.7m2 by pressure grouting because the cohesion of slope in loose soil or highly weathered rocks can not be more than 3.0 t/m2.

2 2 ) ) 2 2 1.5 1.5

1 1

0.5 0.5 BST결과 환산값 소요 점착력 증가량(t/m

소요 점착력 증가량(t/m BST결과 환산값 L=8m L=8m L=6m L=6m 0 0 012345012345 2 원지반 점착력(t/m2) 원지반 점착력(t/m ) (a) slope angle=1:0.5 (b) slope angle=1:0.5 Figure 3.5 Required Cohesion Increment against Cohesion of Original Ground

The cohesion increment is calculated from the borehole shear test results. The overlap effect at the center point between 2.5m spacing holes is ignored since the effective range from grouting hole is assumed to be maximum 1.0m for conservative design. As shown in Figure 3.6, three circles having radius 0.5m, 1.0m, 1.25m, respectively with the same center at grouting hole are utilized to estimated equivalent average cohesion. Average cohesion in domain ① was calculated by averaging the values obtained from 0.5m offset and that of domain ② and ③ were calculated from boundaries of each domain, respectively.

Figure 3.6 Estimation of Equivalent Cohesion of Pressure Grouted Ground

14 The equivalent cohesion increment by pressure grouting is 1.8 t/m2, which is slightly bigger than required cohesion increment 1.7 t/m2 when the nail space is changed from 1.5m × 1.5m to 2.5m × 2.5m. Therefore slope in loose soils or highly weathered rocks satisfying required factor of safety with 1.5m×1.5m spacing will also achieve same factor of safety using pressure grouting and 2.5m×2.5m spacing. Above mentioned example is for slope having specific soil properties. Therefore further experiments on various ground condition should be carried out for the proposed design method to be in more general term.

3.3 Application Example on Imaginary Slope Slope stability analysis was carried out both considering the improving effect of pressure grouting and reinforcing effect of FRP nails. Imaginary loose soil slope having 1:1 slope angle and 18m height and highly weathered rock slope having 1:0.7 slope angle and 25m height were used. The space between nails was assumed 2.5m × 2.5m. Both slopes were assumed to have single soil layer and soil properties are listed in Table 3.2. TARLEN program was used to analyze stability of slopes.

Table 3.2 Soil Properties Unit weight (t/m3) Cohesion (t/m2) Friction angle Loose soil 1.9 1 31 Weather rock 2.1 3 32

Figure 3.7 Cross Section of Slope

Both dry season and wet season condition were studied. The ground water table was assumed to be below 3m from ground surface. Stability analysis results of both slopes were 1.13, 1.23 respectively for dry season condition; 0.84, 0.91 respectively for wet season condition. Stabilizing of slopes using FRP grouting method was applied to both slopes since factor of safety without reinforcing method is

15 below required minimum factor of safety for both slopes. Tensile and shear strength of FRP nail were assumed to be 3.3 ton/EA, 11.5 ton/EA, respectively. And also improved zone by grouting was arranged.

(a) Dry season (FS = 1.13) in loose soil (b) Wet season (FS = 0.84) in loose soil

(c) Dry season (FS = 1.23) in weather rock (d) Wet season (FS = 0.91) in weathered rock Figure 3.8 Results of Slope Stability Analysis for Original Slopes

Results of slope stability analysis in reinforced slopes are summarized in Table 3.3 and Figure 3.9. The cohesion increment was assumed to 1.1 t/m2 in loose soil and 1.2 t/m2 in weathered rock, respectively. And factor of safety of each slope is 1.68 in soil slope and 1.63 in rock slope for dry season. And for the wet season the factor of safety was calculated to be 1.2 in both slopes. Therefore both slopes satisfied required minimum factor of safety (1.5 for dry season, 1.2 for wet season).

Table 3.3 Results of Slope Stability Analysis for Reinforced Slopes Cohesion Cohesion increment Factor of Rainy condition 2 2 (t/m ) (t/m ) safety Soil Dry 1.0 1.1 1.68 slope Wet 1.0 1.1 1.20 Rock Dry 3.0 1.2 1.63 slope Wet 3.0 1.2 1.20

16

(a) Dry season (FS = 1.68) in loose soil (b) Wet season (FS = 1.20) in loose soil

(c) Dry season (FS = 1.63) in weather rock (d) Wet season (FS = 1.20) in weathered rock Figure 3.9 Results of Slope Stability Analysis for Reinforced Slopes

3.4 Soil Strength Increment against FRP Nail Space Shear strength increment due to pressure grouting will be changed depending upon the space between FRP nails. In this research, therefore, strength increment against FRP nail space based on results of in situ trial test will be presented. Cohesion increment measured at 0.5m offset and 1.0m offset from center of FRP nail are listed in Table 3.4. Cohesion change against offset distance from center of FRP nail is summarized in Figure 3.10.

Table 3.4 Cohesion Increment against Offset from FRP Hole Offset from FRP hole 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.0 (m) Cohesion Increment 1.2 1.4 2.1 3.9 0 0.8 1.5 4.5 (t/m2)

17 2.5 2.5 5

2 2 4 y = -0.8333x + 1.9833

1.5 1.5 3 y = -1.8667x + 2.5333 1 y = -1.6x + 2.3667 1 2

0.5 0.5 1

0 0 0 0 0.25 0.5 0.75 1 1.25 1.5 0 0.25 0.5 0.75 1 1.25 1.5 0 0.25 0.5 0.75 1 1.25 1.5 Trend 1 Trend 2 Trend 3 Maximum value excluded Maximum value excluded, Maximum value excluded, zero value at 1m offset excluded No increment at 1.25m offset

3 2.5 3.5 y = -1.6151x + 2.4453 y = -1.42x + 2.35 3 2.5 2 2.5 2 1.5 2 y = -2.0368x + 3.05 1.5 1 1.5 1 1 0.5 0.5 0.5 0 0 0 0 0.25 0.5 0.75 1 1.25 1.5 0 0.25 0.5 0.75 1 1.25 1.5 0 0.25 0.5 0.75 1 1.25 1.5

Trend 4 Trend 5 Trend 6 Maximum value excluded, Maximum value excluded, Maximum and minimum values zero value at 1m offset excluded, zero value at 1m offset excluded excluded, No increment at 1.25m offset No increment at 1.5m offset No increment at 1.5m offset Figure 3.10 Trend of Cohesion Increment against Offset from FRP Hole

Effective reinforcing area was set to be half of FRP nail space neglecting overlap effect of pressure grouting for conservative design. And cohesion increment was calculated by using cohesion values within effective reinforcing area. Figure 3.11 shows an example of obtaining average cohesion increment in the case of 2.5m ⅹ 2.5m nail spacing using Trend 6.

Average cohesion increment (FRP Pipe Space=2.5m×2.5m)

3.5

3

2.5 y = -2.0368x + 3.05 2

1.5

1

0.5

0 0 0.25 0.5 0.75 1 1.25 1.5 Effective reinforcing area is 1.25m since FRP nail space is 2.5m×2.5m. Comment Therefore calculated average cohesion increment is 1.77 t/m2 Figure 3.11 Calculation Example of Average Cohesion Increment

18 Average cohesion increment against FRP nail space is summarized in Table 3.5 for 6 trends in Figure 3.10.

Table 3.5 Average Cohesion Increment (t/m2) Space Effective area Trend 1 Trend 2 Trend 3 Trend 4 Trend 5 Trend 6 (m) (m) 1.5×1.5 0.75 1.8 1.7 1.8 1.8 1.8 2.28 2.0×2.0 1.0 1.6 1.6 1.6 1.6 1.7 2.03 2.5×2.5 1.25 1.4 1.5 1.4 1.4 1.5 1.77 3.0×3.0 1.5 1.2 1.4 1.1 1.2 1.3 1.52

Cohesion increments using above mentioned results are summarized in Table 3.6. Cohesion increments listed in Table 3.6 are obtained from specific ground condition and limited numbers of test. Therefore more extensive in situ tests should be carried out further for the results to be more general and reasonable.

Table 3.6 Cohesion Increment in Various Ground Condition against FRP Pipe Space After reinforcing Reinforcement Application Friction angle(ø) space (m) Cohesion increment (t/㎡) (°) 1.5 × 1.5 1.7 ～ 2.3 Sandy soil, 2.0 × 2.0 1.6 ～ 2.0 Weathered rock, No Change 2.5 × 2.5 1.4 ～ 1.8 Fracture zone in rock. 3.0 × 3.0 1.1 ～ 1.5

4. Material Specification Materials used in FRP grouting method consist of FRP nail, coupler, caulking material, sealing material, and injection material and following material specification and standard should be observed.

4.1 FRP Pipe 4.1.1 Manufacturing Process and Material Characteristics of FRP Pipe Manufacturing process of FRP pipe can be either way. One way consists of series of wrapping process where unidirectional mat made of glass fiber is submerged in resin and filament winding process where glass fiber roving is winded around the outside pipe. Alternative way is the pultrusion process where multiple stitch mat

19 fabricated by inclined and vertical direction glass fiber are layered and roving fiber submerged in compound are inserted between layered mats in longitudinal direction. Material specifications for pipe are as follows:

Table 4.1 Material Specification of FRP Pipe Glass fiber content Over 60% (KS F 2244-95) Tensile strength Over 350MPa (KS F 2241-99) Bending stiffness Over 150Mpa (KS F 2242-99) Shear strength Over 130Mpa (KS F 2248-90)

4.1.2 Dimension of FRP Pipe

Table 4.2 Dimension of FRP Pipe Item Dimension Spacing between Spacer 1,000mm±100mm 1,000mm±100mm(in 4 directions) Spacing between Injection Hole 500mm±50mm (in 2 directions) Dimension of Spacer Outer diameter: over ø67mm Inner diameter: over ø37mm Dimension of Injection Pipe Thickness: over 4.0mm

4.1.3 Injection Hole ① the purpose of injection of hole is for the sealing material to be injected into the ground by packer pressure. ② Spacing and location of injection hole is as follows: - Spacing: 1,000mm±100mm (in 4 directions), 500mm±50mm (in 2 directions) - Location: Point apart from location of spacer center by 50mm±10mm and in 4 radial directions at that point, Point in the middle of two spacers and in 2 radial directions at that point ③ Diameter of Injection Hole: ø5mm±1mm

4.2 Coupler The material of coupler should be the same as FRP pipe and dimension of coupler is as follows: ① Thickness: over 5.0mm ② Length: 300mm±30mm

20 4.3 Caulking Material The material of caulking is a cement having no shrinkage and normally Ceromax CX-1 or SSA-C or materials corresponding to them are used to endure the maximum pressure of 40 kg/cm2 during the injection procedure.

4.4 Sealing Material Sealing material consists of cement and FRC-1 admixture of which purpose is to prevent injected grouting from flowing toward the entrance of drilled hole. The unconfined compression of 7 days curing should be more than 100 ㎏/㎠, 28 days curing more than 210 ㎏/㎠. Mixing ratio can be adjusted depending upon geological condition and trial test of site, and standard mixing ratio is as follows.

Table 4.3 Mixing Ratio of Sealing Material Total Volume Cement FRC-1 Water W/C Items Remarks (ℓ) (㎏) (㎏) (ℓ) (%) Mixing 1,000ℓ 1,290 12.9 586 45 Ratio

4.5 Injecting Material (High strength grouting) Grouting material is normally mixture of Portland cement and FRC-1 and some admixture for rapid cementation can be used when the amount of injecting material is over 30% than designated amount. Standard mixing ratio of high strength and admixture is as follows.

Table 4.4 Standard Mixing Ratio of Grouting 1,000ℓ / Batch Items Remarks Cement (㎏) Water (ℓ) FRC-1 (㎏) Mixing Ratio 500 839 5.0

Table 4.5 Standard Mixing Ratio of Admixture Liquid A Liquid B

Items Volume(ℓ) SiO2 Water Cement Water W/C Remarks (ℓ) (ℓ) (㎏) (ℓ) (%) Mixing 1,000ℓ 250 250 250 420 168 Ratio

21 4.6 Cap Plate and Nut Cap plate is made of 9mm thick steel plate for FRP nail to be tightened to ground surface, of which dimension is 200mm×200mm having 53mm diameter at center. The cap plate can be omitted depending upon the ground condition.

5. Experiment on FRP Pipes Tensile and shear strength of FRP pipe are required in limit equilibrium slope analysis on slopes reinforced with FRP grouting method, and Young’s modulus and Poisson’s ratio are needed additionally in numerical analysis based on continuum mechanics. The strengths and material properties of FRP pipe are summarized as below.

5.1 Tensile strength Maximum tensile strength of FRP pipe manufactured by UDMAT + filament winding process using C Type resin is 25.04 ton ~ 26.67 ton. Average tensile strength from 3 samples is 25.67 ton and maximum deviation is about 7%. Allowable tensile strength can be obtained by following equation 5.1 if assumed manufacturing tolerance is 10% and factor of safety is set to 2.

n T 0.9 × 25.65 T = t u = ≈11.5 ton (5.1) a FS 2

Where,

Tu = average maximum tensile strength (ton) nt = manufacturing tolerance

Ta = allowable tensile strength 5.2 Shear Strength Maximum tensile strength of FRP pipe manufactured by UDMAT + filament winding process using C Type resin is 7.5 ton. Allowable tensile strength can be obtained by following equation 5.2 if assumed manufacturing tolerance is 10% and factor of safety is set to 2.

22 n S 0.9× 7.5 S = s y = ≈ 3.3 ton (5.2) a FS 2 Where,

Sy = average shear strength (ton), ns = manufacturing tolerance

Sa = allowable shear strength (ton)

5.3 Summary of FRP Pipe Properties Properties of FRP pipe can be summarized as follows.

Table 5.1 Properties of FRP Pipe Items unit suggest value allowable tensile strength ton/ea 11.5 allowable shear strength ton/ea 3.3 Elastic modulus t/m2 5,360,000 Poisson's ratio - 0.35

6. Laboratory Pullout Test for Bond Experiment on FRP Pipes 6.1 Purpose of Experiment The objective of laboratory model tests was to investigate the pullout resistance of FRP pipes and the expansion effects of radius drilled hole to the confining pressure. The variables for the tests were relative density of the soil, injection pressure. Figure 6.1 shows the set-up of laboratory model tests consist of a cylindrical tank, a manometer, a grout injector, a cutter, a regulator.

Figure 6.1 Set-up of laboratory model tests.

23 6.2 Test Method

6.2.1 Modeling of soil The model of soil layers made up the residual soil of so-called Seoul granite which obtained in Naksungdae, Seoul. The physical and mechanical properties of the residual soil are summarized in Table 6.1.

Table 6.1 Test Plan unit weight relative density injection pressure confining pressure Classification (t/m3) (%) (%) (kg/cm2) (kg/cm2) d16 1.6 50 8～10 10 0.5, 1.0, 1.5 d18 1.8 80 8～10 10 0.5, 1.0, 1.5

6.2.2 Installation of the FRP pipes After the build-up the model of soil layers, the drilling is advanced sequentially by a) opening the down cover of the tank, b) driving the rotary cutter in 90mm diameter into the central part of soil layers. The device of rotary cutting is consisted of a motor having 10ton in capacity and a regulator to stand a constant rotary speed for the minimum disturbance of soil layers. Completing the drill holes, the FRP pipes with the four injection holes devised for cement milk grouting, they are taped or covered with rubber band for preventing the seals or the slimes from infiltrating into the pipes, are inserted in the drilled holes after closing the down cover of the tank as shown Fig. 13.

Figure 6.2 Installation of FRP Pipe

24 6.2.3 Sealing and the pressure injection grouting The space between the outer diameter of drilled hole and FRP pipe is filled with the seals, the cement milk grout was injected into the soil layer modeled through the injection holes in the FRP pipe with a grout injector in connection with cylindrical tank. The injection pressure increased to 10.0kg/cm2 by 2.0kg/cm2 per minute during the 5minutes(Kleyner et al., 1993). Also, the injection of was made under the confined condition of 0.5kg/cm2, 1. 0kg/cm2 and 1.5kg/cm2. The consolidating cement with a super-high speed is known that uniaxial compression strength of the cement consolidated for one day is almost equal with that of the Portland cement consolidated for seven days was used in order to diminish the test period. The mixture ratio of the seals and the cement milk grouts used in modeled test summarized in Table 6.2.

Figure 6.3 Uniaxial compression strength of cement vs. Curing Period

Table 6.2 Mixing Ratio of Sealing and Grouting Sealing material cement suspension grout cement 1.3 kg 0.5 kg water 587 ml 841 ml W/C (%) 45% 168%

6.2.4 Pullout resistance tests The objective of pullout tests was investigated the pullout performance and the bond characteristics of the FRP pipe to cement grout. As a general rule, the pullout tests in site are executed in 7 days after the cement grout. Since the seals and the grouts

25 mixed with the consolidating cement with a super-high speed mentioned above, the pullout resistance tests were executed in elapsed 24 hours after the grouting. Since the condition of tests is different from that of site pullout test, the tests were executed by the method pushing FRP pipe down under the same condition that the confining pressure was adjusted during the grouting as shown Figure 6.4.

Figure 6.4 Setup of Bond Test

6.2.5 Expansion diameter of drilled hole, moisture content ratio, unit weight. The diameter of the grouted body was measured in order to investigate the expansion effect of drilled hole by the injection pressure in relation to the confining pressure. Also, the moisture content and unit weight of modeled soil layer were measured by withdrawing the cans were installed in modeled soil layer.

6.3 Test Results and Discussion The expansion diameters of drilled hole in relation to confining pressure and pullout resistance in modeled soil layer with a unit weight 1.6t/m3 were summarized in Table 6.3 and Figure 6.5. As the results of test, the pullout resistance is the range from 0.04kg/cm2 to 0.17kg/cm2, there is no relationship between pullout resistance and confining pressure, and the load transfer from FRP pipe to the grout depends mainly on the adhesion and mechanical interlocking according to the shape of injection grouted body by pressure. The relationship between expanded radius and confining pressure summarized in Figure 6.6. This indicates that the increasing of confining pressure tends toward the decrease of expanded radius by the pressurized injection grouting.

26 Table 6.3 Results of Laboratory Pullout Test Confining Maximum pull-out Increasing hole Unit weight Water content* Items pressure stress size (t/m3) (%) (kg/cm2) (kg/cm2) (cm) d16c05-1 1.60 0.5 8.3 0.1299 - d16c05-2 1.59 0.5 9.1 0.0349 - d16c05-3 1.61 0.5 10.1 0.1478 1.610 d16c10-1 1.65 1.0 10.0 0.0834 0.675 d16c10-2 1.60 1.0 11.6 0.0475 0.925 d16c10-3 1.63 1.0 8.8 0.1026 0.825 d16c15-1 1.65 1.5 10.6 0.1317 0.050 d16c15-2 1.64 1.5 9.6 0.1468 0.950 d16c15-3 1.61 1.5 8.6 0.1291 1.028 d18c05-1 1.60 0.5 10.2 0.2262 2.430 d18c05-2 1.59 0.5 10.2 0.2960 0.390 d18c05-3 1.61 0.5 8.9 0.3560 0.443 d18c10-1 1.65 1.0 7.9 0.1156 0.048 d18c10-2 1.60 1.0 8.0 0.1642 0.095 d18c10-3 1.63 1.0 9.0 0.1999 0.535 d18c15-1 1.65 1.5 9.8 0.3627 0.960 d18c15-2 1.64 1.5 8.8 0.3113 0.410 d18c15-3 1.61 1.5 8.0 0.3446 0.120

d16c05-1 d16c10-1 d16c15-1 d18c05-1 d18c10-1 d18c15-1 d16c05-2 d16c10-2 d16c15-2 d18c05-2 d18c10-2 d18c15-2 d16c05-3 d16c10-3 d16c15-3 d18c05-3 d18c10-3 d18c15-3 0.2 0.4

0.16 2

2 0.3

0.12

0.2 0.08

0.1 Pullout resistance (kg/cm ) (kg/cm resistance Pullout

0.04 Pullout resistance (kg/cm )

0 0 01020300 102030 Displacement (mm) Displacement (mm) (a) Pullout Test Result (Dr=50%) (b) Pullout Test Result (Dr=80%) Figure 6.5 Results of Pullout Test

27 2.5 2.5

2 2

1.5 1.5

1 1

0.5 0.5 Expanded radius (cm) Expanded radius (cm) Expanded 0 0 00.511.52 0 0.5 1 1.5 2 Confining pressure (kg/cm2 ) Confining pressure (kg/cm2 ) (a) Dr=50% (b) Dr=80% Figure 6.6 Expansion of Hole vs. Confining Pressure

7. In Situ Testing In situ testing such as pressuremeter tests, the permeability tests and the borehole shear tests are conducted for the purpose of the quantitative evaluation of the effects of the reinforced grouting method using FRP pipes. The testing holes were planed at 0.5m and 1.0m cross over distance from the drilled holes for the reinforced grouting using FRP pipes as shown Figure 7.1, the used injection pipes is the same as the FRP pipes were manufactured by the process ‘UDMAT + Filament winding’. The underground is composed of the residual soil within 4.0m thickness and the highly weathered rock of the biotite granite.

7.1 Pressuremeter Testing The borehole pressuremeter tests (PMT) are used to measure the in situ deformation(compressibility) and strength properties of a wide variety of soil types, weathered rock and low to moderate strength intact rock. These test were conducted for the residual soil in 2.0m depths and the weathered rock in 5.5m depths. The tests were carried out using the ELASTMETER-2(made by OYO corporation in Japan) in case of the before and after grouting. The deformation modulus and elastic modulus calculated by the tests were summarized in Table 7.1. According to the results of the tests, the deformation modulus of the grouted ground has high increased in comparison with that of the natural ground. Judging the result of pressuremeter, the reinforced cement grouting using the FRP pipes is to be an effective method in respect to the increase of the ground strength.

28

Figure 7.1 In situ test layout

7.2 Borehole Shear Tests The borehole shear test is the most rapid soil strength test that separately determines both a soil cohesion and an angle of internal friction. It is the only in situ test that measures both of these fundamental soil strength parameters in order to avoid laboratory bias introduced by poor samples. In this paper, the borehole shear tests were executed to evaluate the increment of soil strength parameters to the result of the reinforced cement injection grouting using the FRP pipes (Lutenegger et al., 1978). The tests were performed in 3.0inch diameter machine-bored 9 holes (before grouting; 1 bored hole, after grouting ; 8 bored holes) at the depth 2.0m. The strength parameters were summarized in Table 7.2. In comparison with the soil strength parameter of the before and after grouting, the angles of internal friction are almost no difference but the soil cohesions are high increased to 2.6times in maximum at a position. To express the variation of cohesion and an internal friction angle as a parameter, the shearing strengths at the depth performed the tests were calculated by the Mohr-Coulomb’s failure equation on the supposition that the unit weight of a residual soil is 1.8t/m3. The shear strengths of the residual soil measured after grouting at 0.5m and 1.0m cross over distance from the FRP pipes has increased respectively by 100%, 70% in average in comparison with those of the measured before grouting as shown Figure 7.2.

29

Figure 7.2 Change of Shear Strength before and after grouting

Table 7.1 Summary of the pressuremeter test results. Deformation Elastic Crossover Tested Borehole No. modulus(D) modulus(E) Descriptio distance depth (kg/cm2) (kg/cm2) n (m) (m) Residual BH-1 30.01 44.41 soil - 2.0 (before grouting) 220.73 - C. W. R. - 5.5 GH-1 (after grouting) 117.07 222.84 Residual 1.0 2.0 GH-5 148.54 327.87 soil 0.5 GH-1 679.19 1,144.96 1.0 GH-5 769.35 1,770.35 C. W. R. 0.5 5.5 GH-2 200.27 245.35 Residual 1.0 GH-6 202.69 354.98 soil 0.5 2.0 GH-2 642.87 1,051.16 1.0 GH-6 752.73 1,243.38 C. W. R. 0.5 5.5 GH-3 197.04 537.44 Residual 1.0 GH-7 220.98 632.56 soil 0.5 2.0 GH-3 686.51 1,072.70 1.0 GH-7 620.01 1,133.66 C. W. R. 0.5 5.5 GH-4 193.08 569.39 Residual 1.0 GH-8 215.00 609.28 soil 0.5 2.0 GH-4 740.04 1,329.70 1.0 GH-8 835.12 1,729.93 C. W. R. 0.5 5.5

Table 7.2 Summary of the borehole shear test results. Hole No. Hole No. (before Items (after grouting) grouting) BH-1 GH-1 GH-2 GH-3 GH-4 GH-5 GH-6 GH-7 GH-8 Cohesion ( t/m2 ) 1.5 1.5 2.3 3.0 6.0 2.7 2.9 3.6 5.4 friction angle( o ) 17.6 17.7 20.6 15.0 20.3 16.2 19.6 14.7 21.4

30