Hybrid TBM takes on Australian Decline Tunnel

On Dec. 20, 2013, an 8.0-m (26.2-ft) diameter Robbins Hybrid Single Shield/EPB TBM was launched to bore the Grosvenor Decline Tunnelfor Australia’s Anglo-American Coal Mine. The machine was built using OnsiteFirst Time Assembly (OFTA) in order to fit within a tight project schedule.Assembly at the remote jobsite near Moranbah, Australia took about four and ahalf months, and then the machine was walked down into a launch tunnel.

Two decline tunnels, at grades of 1:6 and 1:8, will beused for mine access to new coal seams. The hybrid machine is tackling mixedground conditions ranging from sand and clay to varying types of sedimentary hard rock up to120 MPa UCS, as well as coal seams.  Methane gas is expected to be present throughout the tunnel,so the machine has been designed as Explosion Proof Compliant to ERZ-1. “Grosvenoris the first underground coal mine in Queensland to use a TBM for driftconstruction,” said Glenn Tonkin, Grosvenor Project Director. “We are proud tobe pioneering this technology.”

Robbins Hybrid Single Shield/EPB TBMOnly about 300 m (984 ft) of ground in each decline tunnelare expected to require EPB mode, while the rest of the tunnel will be bored inhard rock mode. Thus, the design was optimized toward hard rock excavation.
In EPB mode, the machine uses a two-stage, center-mountedscrew to deal with watery muck. One screw conveyor will run faster than theother, creating a muck plug that will push water out of the screw conveyor. Themachine’s mixed ground cutterhead is fitted with interchangeable knife bits anddisc cutters. In addition, the cutterhead is clad with extensive wear platesfor abrasion protection. The mixing chamber can be filled with water, foam andother additives to keep it spark-safe in the presence of methane.

“The machine essentially uses its EPB technology to dealwith methane gas safely,” said Doug Harding, Robbins Vice President. If any methane leakage is detected, anevacuation system called a “snuffing box” will draw methane out of the end ofthe screw conveyor and directly into the ventilation system. “The TBM tunnelingmethod will deliver advances in safety, higher quality drifts, and fasterproject development,” said Tonkin.

Robbins Hybrid Single Shield/EPB TBMTo convert to hard rock mode, a hydraulically-operated muckchute is deployed around the screw. The muck is picked up by paddles in themuck chamber to load the screw. Interchangeable EPB knife bits will be replacedwith disc cutters on the cutterhead, and the EPB scrapers on the cutterheadmust be replaced with hard rock bucket lips. A skew ring offsets or reacts to the torque of the machinein hard rock, allowing for more efficient single-direction cutterheadexcavation and muck pickup. 

A final unique aspect of the project is a specially-designed“Quick Removal System”. As noground in Australia can be left unsupported and the machine is boring a blindtunnel, it will be able to retract in one piece from its shield, leaving the shieldin place. “The core of the machine is a bolted design that separates from theshield, in a process that does not require a cutting torch,” said Harding. The TBMcore and back-up will then be walked up the decline tunnel on a set of customtransport dollies and moved to the second decline tunnel, where another set ofshields will be waiting for machine assembly prior to launch.

Robbins Hybrid Single Shield/EPB TBM“We commenced tunneling last month and the machinehas advanced more than 100m (328 ft) so far. We are on track to reach pitbottom in the next couple of months. The first few weeks were largely spent commissioningthe machine in compliance with the mine standards. We expect the machinewill perform well and we will achieve the planned cutting rates,” said Tonkin. The machine is expected to completethe first decline tunnel in April 2014.

This article was provided by TheRobbins Co.Robbins Hybrid Single Shield/EPB TBM

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