how megabolts installed as primary support assist in safely improving development rates acarp...

How megabolts installed as primary support assist in

safely improving development rates

ACARP Roadway Development Operators Workshops - October 2011

IntroductionIntroduction

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

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MW9 MegaboltMW9 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

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MW9 – Nth Goonyella face roadMW9 – Nth Goonyella face road

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MW9 advantagesMW9 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

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MW9 advantagesMW9 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

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Important considerationsImportant 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

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MW9 groutingMW9 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

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MW9 groutingMW9 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

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MW9 developmentsMW9 developments

Mechanised insertion ●Lobster from Conway Engineering●Being used at Angus Place●Favourable reports so far

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MW9 developmentsMW9 developments

Resin grouting using Minova Carbothix●Immediate roof support●Remote pumping●Quicker grouting

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Megaflex TTXMegaflex 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

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TTX – advantagesTTX – advantages

● No exposure to high pressure tensioner hydraulics

● Reduced injuries from handling tensioners

● Quicker installation than hydraulically tensioned cables

● Combo dolly

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Combo dolly – no changing dolliesCombo dolly – no changing dollies

MixingInner socket engages hex drive

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TighteningOuter socket engages nut

TTX – advantagesTTX – 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

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TTX – advantagesTTX – 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%

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TTX – advantagesTTX – advantages

● Increased load transfer from spiral wire

● Groutable version being developed – will require 42 mm dia. hole

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Limitations of torque-tensioned cablesLimitations 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

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Groutable FG rib boltGroutable 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

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Groutable FG rib dowel - advantagesGroutable FG rib 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

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