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.
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OVERVIEW
Jurong Cavern: Introduction
Fiber Reinforced Polymer (FRP) rockbolts vs. Steel bolts
Laboratory and field characterization
Numerical modeling (UDEC) results
Conclusions
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CAVERN LOCATION (JURONG
ISLAND)
CAVERN LAYOUT (PHASE 1)
TYPICAL STORAGE GALLERY
TYPICAL
STORAGE
GALLERY
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 0.36
MPa
Design life of 50 years
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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 cementgrouted, 346-kN tensile and 160-kN shear capacity)
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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
ADVANTAGES OF FRP BOLTS
(CONTD.)
Lower stiffness
(third) of FRP
bolt allows three
times more
deformation
compared to
steel bolts)
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
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LABORATORY CHARACTERIZATION
Parameter
Breaking load (kN)
Value
358
Tensile strength (MPa)
1,035
Young’s modulus (GPa)
44.13
Maximum strain (%)
2.35
IN-SITU SHORT ENCAPSULATION
TEST (SEPT) RESULTS
Hole
Condition
Dry
Wet
Grout Cure
Time
(hours)
Failure Load
(kN)
Failure
Mode
6
110
Grout
12
185
Thread
24
225
Thread
6
50
Grout
12
270
Thread
24
250
Thread
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NUMERICAL MODELING
RESULTS
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MODELED ROCK PROPERTIES
Rock Type
Proportion
of Rock
Mass
(%)
Uniaxial
Rock
Compressive Young’s
Quality
Strength
Designation
Modulus
(MPa)
(RQD)
(GPa)
Weathered rock
23
36
130
46.3
Sandstone
51
98
117
65.6
Siltstone
10
100
174
40.3
Alternating
sandstone/siltstone
16
100
162
71.4
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MODELED ROCKBOLT
PROPERTIES
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)
346
240
Bolt shear load (kN)
160
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
Parameter
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YIELD CONDITION (UNBOLTED CASE)
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YIELD CONDITION (STEEL BOLTS)
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YIELD CONDITION (FRP BOLTS)
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AXIAL LOAD COMPARISON
Axial Load (kN)
Bolt No.
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
89
Bolt 10
34
35
Bolt 11
47
41
Bolt 12
55
64
Bolt 13
42
45
Bolt 14
20
24
Bolt 15
4
2
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AXIAL LOAD COMPARISON
Axial Load (kN)
Bolt No.
Bolt 16
Steel Bolt/Resin Grout
2
FRP Bolt/Cement Grout
1
Bolt 17
165*
188
Bolt 18
165*
277
Bolt 19
74
94
Bolt 20
165*
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
14
22
Bolt 28
15
22
Bolt 29
21
41
Bolt 30
14
24
Bolt 31
15
35
*At yield load.
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Mining & Civil Engineers & Geologists
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
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