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How megabolts installed as primary support assist in safely improving development rates

How megabolts installed as primary support assist in safely improving development rates. Introduction. Three types of megabolts installed from continuous miner Post grouted megastrands – MW9 Resin anchored, torque-tensioned megaflex bolts - TTX

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How megabolts installed as primary support assist in safely improving development rates

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  1. How megabolts installed as primary support assist in safely improving development rates ACARP Roadway Development Operators Workshops - October 2011

  2. Introduction • Three types of megabolts installed from continuous miner • Post grouted megastrands – MW9 • Resin anchored, torque-tensioned megaflex bolts - TTX • Resin anchored, post groutable fibreglass rib bolts ACARP Roadway Development Operators Workshops - October 2011

  3. MW9 Megabolt • Most commonly installed megabolt is the barrel & wedge version – MW9 • Fully bulbed using spiral rib wire for max load transfer • Up to 11 m long cables installed from miner in LW installation roads ACARP Roadway Development Operators Workshops - October 2011

  4. MW9 – Nth Goonyella face road ACARP Roadway Development Operators Workshops - October 2011

  5. MW9 advantages • 42 mm hole – no reaming • Single 1,000 mm resin capsule with resin retainer • Resin pushed up hole with bolt – no conduit • Collar fittings attached after bolt installed • No bearing plate or bolt head to catch on walkway ACARP Roadway Development Operators Workshop 2011

  6. MW9 advantages • Tension within 5 mins of installation • Tension using system hydraulics or intensifier • 9 to 20 t pre-tension can be achieved depending whether system hydraulics or intensifier used • No air needed on miner • Provides immediate point anchor support of 57 t ACARP Roadway Development Operators Workshop 2011

  7. Important considerations • Bolt is point anchored until grouted • Anchor length designed to take capacity of bolt – depends on rock type at anchor horizon • Pull tests must be done to determine if anchor can take full capacity of bolt • This ungrouted bolt is loaded to 45-50 tonnes ACARP Roadway Development Operators Workshop 2011

  8. MW9 grouting • Top down grouted using grout lance – quickest grouting method • Grouting done within designated time or distance advanced – depends on conditions • Heavy conditions may require grouting within 24 hrs • Good conditions (intersections) can be left for more than a week ACARP Roadway Development Operators Workshop 2011

  9. MW9 grouting • Grout generally reaches sufficient strength (30 to 40 MPa) within 24 hrs • Readily & easily audited • Regular auditing has greatly improved quality of installation • Grouting non-compliance now less than 5% • Good installation reduces likelihood of remedial roof support ACARP Roadway Development Operators Workshop 2011

  10. MW9 developments Mechanised insertion • Lobster from Conway Engineering • Being used at Angus Place • Favourable reports so far ACARP Roadway Development Operators Workshop 2011

  11. MW9 developments Resin grouting using Minova Carbothix • Immediate roof support • Remote pumping • Quicker grouting ACARP Roadway Development Operators Workshop 2011

  12. Megaflex TTX • Torque-tensioned • TT bolt becoming more in demand • 56 t and 48 t versions • 56 t generally requires 28 mm hole • 48 t a 27 mm hole ACARP Roadway Development Operators Workshop 2011

  13. TTX – advantages • No exposure to high pressure tensioner hydraulics • Reduced injuries from handling tensioners • Quicker installation than hydraulically tensioned cables • Combo dolly ACARP Roadway Development Operators Workshops - October 2011

  14. Combo dolly – no changing dollies Mixing Inner socket engages hex drive Tightening Outer socket engages nut ACARP Roadway Development Operators Workshops - October 2011

  15. TTX – advantages • Roller race between nut & washer reduces friction • Race is shrouded to keep bearing free of dirt or mud • 7 t bolt tension from 320 Nm drill torque • Minimal protrusion from roof – important in low seams • Removing hex drive reduces protrusion further – as little as 115 mm ACARP Roadway Development Operators Workshop 2011

  16. TTX – advantages • Wires are anchored in the bolt head using button heads forged on end of each wire – maintains max collar strength • B&W anchor typically reduces cable collar capacity by approx 10% ACARP Roadway Development Operators Workshop 2011

  17. TTX – advantages • Increased load transfer from spiral wire • Groutable version being developed – will require 42 mm dia. hole ACARP Roadway Development Operators Workshop 2011

  18. Limitations of torque-tensioned cables • Reduced bolt pre-tension compared to hydraulic tensioning • Possible use of torque multipliers • Slows down installation • Failure of torque multiplier can delay production • Possible safety issues • May need modifications to head-plate of drill mast to accommodate bolt and/or dolly • Full resin encapsulation difficult for cables > 4 m • Load transfer lower than for bulbed cables • If bulbed then larger hole dia. & bigger resin capsule ACARP Roadway Development Operators Workshop 2011

  19. Groutable FG rib bolt • 42 t capacity • Cuttable • 42-45 mm drill hole • Point anchored initially • Breakout nut • High torsion strength – stalls rib bolting rigs • 17 t collar capacity • Shear strength of 14 t • SG of 1.9 to 2.1 – separates in washery ACARP Roadway Development Operators Workshops - October 2011

  20. Groutable FGrib dowel - advantages • Immediate rib support • Hollow centre - post groutable with thixotropic grout • Full encapsulation vital in heavy rib conditions • Easily audited • No secondary rib support required – maximises development rates ACARP Roadway Development Operators Workshops - October 2011

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