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FIBER REINFORCED POLYMER ROCKBOLTS FOR GROUND CONTROL IN STRONG JOINTED ROCK MASS Samrat Mohanty, PhD, PE, Senior Engineer, Agapito Associates, Inc., Golden,

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Presentation on theme: "FIBER REINFORCED POLYMER ROCKBOLTS FOR GROUND CONTROL IN STRONG JOINTED ROCK MASS Samrat Mohanty, PhD, PE, Senior Engineer, Agapito Associates, Inc., Golden,"— Presentation transcript:

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

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 m 3 Storage galleries excavated by Drill and Blast in three 9-m-high cuts (top heading and two benches) Additional excavations totaling 0.7 million m 3 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

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 ParameterValue 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 Dry6110Grout 12185Thread 24225Thread Wet650Grout 12270Thread 24250Thread 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 rock233613046.3 Sandstone519811765.6 Siltstone1010017440.3 Alternating sandstone/siltstone 1610016271.4 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

16 MODELED ROCKBOLT PROPERTIES Parameter FRP Bolt/ Cement Grout Steel Bolt/ Resin Grout Bolt diameter (mm)2522 Bolt density (kg/m 3 )2,2007,800 Bolt Young's modulus (GPa)50200 Bolt yield load (kN)346160 Bolt ultimate load (kN)346240 Bolt shear load (kN)16080 Grout bond shear stiffness (N/m/m)1.0 × 10 8 1.12× 10 7 Grout shear strength (N/m)1.88 × 10 5 1.75 × 10 5 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

17 YIELD CONDITION (UNBOLTED CASE) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

18 YIELD CONDITION (STEEL BOLTS) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

19 YIELD CONDITION (FRP BOLTS) AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

20 AXIAL LOAD COMPARISON Bolt No. Axial Load (kN) Steel Bolt/Resin GroutFRP Bolt/Cement Grout Bolt 1 1027 Bolt 2 1216 Bolt 3 3034 Bolt 4 5969 Bolt 5 81113 Bolt 6 7080 Bolt 7 97142 Bolt 8 89176 Bolt 9 9489 Bolt 10 3435 Bolt 11 4741 Bolt 12 5564 Bolt 13 4245 Bolt 14 2024 Bolt 15 42 AGAPITO ASSOCIATES, INC. Mining & Civil Engineers & Geologists

21 AXIAL LOAD COMPARISON Bolt No. Axial Load (kN) Steel Bolt/Resin GroutFRP Bolt/Cement Grout Bolt 16 21 Bolt 17 165*188 Bolt 18 165*277 Bolt 19 7494 Bolt 20 165*253 Bolt 21 1455 Bolt 22 3651 Bolt 23 3343 Bolt 24 5053 Bolt 25 3032 Bolt 26 2239 Bolt 27 1422 Bolt 28 1522 Bolt 29 2141 Bolt 30 1424 Bolt 31 1535 *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


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