1. Fiber Reinforced Polymer RockBolts for Ground Control in Strong Jointed Rock Mass
Samrat Mohanty, PhD, PE, Senior Engineer, Agapito Associates, Inc., Golden, CO
Tom Vandergrift, PE, Principal, Agapito Associates, Inc., Golden, CO
Tim Ross, PE, Principal, Agapito Associates, Inc., Golden, CO
Gan Chin Hwi, Project Manager, Parsons Brinckerhoff Pte. Ltd, Singapore
Mee Nee Lee, Project Manager,Parsons Brinckerhoff Pte. Ltd, Singapore
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

2. Overview Jurong Cavern: Introduction
Fiber Reinforced Polymer (FRP) rockbolts vs. Steel bolts
Laboratory and field characterization
Numerical modeling (UDEC) results
Conclusions
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

3. Cavern Location (jurong Island)

4. Cavern Layout (Phase 1)

5. Typical storage gallery

6. Typical storage gallery

7. Cavern Specifications (Phase 1)
Depth below sea level: 119m
Five storage galleries : 20m x 27m x 340m (w x h x l)
Total storage capacity:1.5 million m3
Storage galleries excavated by Drill and Blast in three 9-m-high cuts (top heading and two benches)
Additional excavations totaling 0.7 million m3
Total length of excavations: 12 km
Crude oil, condensate, naphtha and gasoil storage at pressures of MPa
Design life of 50 years
AGAPITO ASSOCIATES, INC.
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8. Cavern Specifications (contd.)
Host rock mass constitute of sandstone, siltstone and alternating sandstone/siltstone
Ground support (systematic bolting, systematic bolting with shotcrete, spot bolting) based on Q-System
Excavations mapped round-by-round and appropriate ground support installed
Initial design included steel rock bolts (22-mm dia, Grade 60, fully resin-grouted, 160-kN tensile and 80-kN shear capacity)
Revised design included FRP bolts (25-mm dis, fully cement- grouted, 346-kN tensile and 160-kN shear capacity)
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

9. Advantages of FRP Bolts
Produced by embedding continuous glass fibers in a polyester resin matrix
Extruded with a continuous external thread and can be cut to any size
Corrosion resistance and longevity much higher vis-a-vis steel bolts in anticipated high chloride and alkaline environment
Cross-linked molecules of the resin used in FRP bolts become saturated during production, which makes them inert
Density of FRP bolts (28% of steel bolts) allows ease of maneuvering, meaning greater productivity and less injury risk
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

10. Advantages of FRP Bolts (Contd.)
Lower stiffness (third) of FRP bolt allows three times more deformation compared to steel bolts)

11. Disadvantages of FRP Bolts
Low thread strength of FRP Bolts, 180 kN, is generally a weak link; compromising nut and cap. However, thread strength more of an issue in highly dilating soft rock mass. Thread integrity hasn't been compromised at Jurong Caverns due to competent rock matrix and tight joints
Higher cost, but similar to steel bolts with corrosion protection
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

12. Laboratory characterization
Parameter
Value
Breaking load (kN)
358
Tensile strength (MPa)
1,035
Young’s modulus (GPa)
44.13
Maximum strain (%)
2.35

13. in-situ Short encapsulation Test (SEPT) results
Hole Condition
Grout Cure Time
(hours)
Failure Load
(kN)
Failure Mode
Dry 6
110
Grout 12
185
Thread 24
225
Wet 50
270
250
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

14. Numerical Modeling Results
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

15. Modeled Rock properties
Rock Type
Proportion of Rock Mass
(%)
Rock Quality Designation (RQD)
Uniaxial Compressive Strength
(MPa)
Young’s Modulus (GPa)
Weathered rock 23 36
130
46.3
Sandstone 51 98
117
65.6
Siltstone 10
100
174
40.3
Alternating sandstone/siltstone 16
162
71.4
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

16. Modeled Rockbolt properties
Parameter
FRP Bolt/
Cement Grout
Steel Bolt/
Resin Grout
Bolt diameter (mm) 25 22
Bolt density (kg/m3)
2,200
7,800
Bolt Young's modulus (GPa) 50
200
Bolt yield load (kN)
346
160
Bolt ultimate load (kN)
240
Bolt shear load (kN) 80
Grout bond shear stiffness (N/m/m)
1.0 × 108
1.12× 107
Grout shear strength (N/m)
1.88 × 105
1.75 × 105
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17. Yield condition (unbolted case)
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18. Yield condition (steel bolts)
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19. Yield condition (frp bolts)
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20. Axial load comparison Bolt No. Axial Load (kN) Steel Bolt/Resin Grout
FRP Bolt/Cement Grout
Bolt 1 10 27
Bolt 2 12 16
Bolt 3 30 34
Bolt 4 59 69
Bolt 5 81
113
Bolt 6 70 80
Bolt 7 97
142
Bolt 8 89
176
Bolt 9 94
Bolt 10 35
Bolt 11 47 41
Bolt 12 55 64
Bolt 13 42 45
Bolt 14 20 24
Bolt 15 4 2
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

21. Axial load comparison AGAPITO ASSOCIATES, INC. Bolt No.
Axial Load (kN)
Steel Bolt/Resin Grout
FRP Bolt/Cement Grout
Bolt 16 2 1
Bolt 17
165*
188
Bolt 18
277
Bolt 19 74 94
Bolt 20
253
Bolt 21 14 55
Bolt 22 36 51
Bolt 23 33 43
Bolt 24 50 53
Bolt 25 30 32
Bolt 26 22 39
Bolt 27
Bolt 28 15
Bolt 29 21 41
Bolt 30 24
Bolt 31 35
*At yield load.
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists

22. Conclusions
Cement-grouted FRP rock bolts have been used successfully at Jurong Caverns
No significant ground failures in areas systematically supported by FRP bolts, in 5-year construction period till date
FRP bolts advantageous over steel bolts in corrosion resistance, weight, ease of handling, larger allowable deformation and ultimate strength in the unique geotechnical setting at Jurong Caverns
AGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists