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

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

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 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

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

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 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

Laboratory characterization Parameter Value Breaking load (kN) 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 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

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

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

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 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

Yield condition (unbolted case) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

Yield condition (steel bolts) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

Yield condition (frp bolts) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

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

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

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