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Product category: Machine Building Components
News Release from: DavyMarkham | Subject: Tunnel boring components
Edited by the Engineeringtalk Editorial Team on 05 June 2003

Cutterheads speed boring job

The Manufacturing Division of Aker Kvaerner Engineering and Construction has fabricated the forward components for two tunnel boring machines for the final phase of the Channel Tunnel Rail Link.

The Sheffield-based Manufacturing Division of Aker Kvaerner Engineering and Construction has fabricated the forward components for two tunnel boring machines (TBMs) being used on the final phase of the Channel Tunnel Rail Link (CTRL) They were built for Kawasaki Heavy Industries, the global manufacturer of heavy machinery, transportation equipment and industrial goods, and are being deployed by tunnelling contractors Nishimatsu/Cementation/Skanska JV on the 7.5km section between Stratford and St Pancras

The massive 8.11m diameter fabrications, comprising cutterheads, bulkheads, 11.3m long shields and tailskin, form the forward components of the two Kawasaki TBMs.

Each of these machines weighs a total of 1100t, including backup trailers, of which 760t is accounted for by the TBM section itself and a total of 390t were fabricated and supplied by Aker Kvaerner.

Aker Kvaerner E and C has considerable fabrication expertise in this specialist area and its Prince of Wales Road works has the space and resources to accommodate engineering projects on this scale.

Now in its second phase, the GBP 5.2 billion CTRL project is scheduled for completion in 2007 and will halve journey times between central London and the Channel Tunnel, enabling Paris to be reached in around 2h 15min by non-stop Eurostar.

Contract 220, being undertaken by the NCS JV consortium, comprises twin 7.5km bored tunnels from Stratford Box to the London West Portal; the consortium is working closely in conjunction with CTRL designer and project manager, Rail Link Engineering, for the client Union Railways North.

To accommodate train speeds of up to 230km/h, the finished tunnel diameter will be 7.15m, compared with around 5.6m for the normal UK rail system, and it will be lined with steel- and polypropylene-reinforced concrete ring segments.

The Kawasaki-designed TBMs are dual mode devices, which use a closed mode to drive as an earth pressure balance machine through unstable Thanet sands, but are also able to function in an open mode configuration through more stable London clay.

Spoil is removed from the cutterhead chamber by screw conveyor, in both modes of operation.

In closed mode, each TBM is able to retain forward pressure to balance the earth pressure encountered, thus maintaining stability; while in open mode it is capable of removing spoil from the unpressurised head, using a retractable hopper to gather the material rapidly.

The two-speed cutterheads, built by Aker Kvaerner, were fabricated from stress-relieved steel plate and feature abrasive hard facings, produced by special welding techniques.

The cutterhead incorporates tungsten carbide-tipped picks for softer conditions and special alloyed-steel discs, with tungsten carbide tips, for harder ground.

Abrasion resistance is further enhanced by the use of chrome wear-resistant overlay plates, known as 'ING' plates, which were supplied from Japan by Kawasaki and were welded in strategic locations on the cutterhead to protect it from excessive wear.

Adjustable gauge cutters, moved by hydraulic cylinders, allow a variable overcut situation when negotiating curves and these are set to operate within +3mm tolerance of the tunnel diameter.

Kawasaki has also incorporated an hydraulic abrasion detection system that indicates when the surface of the picks and discs are worn and require replacement.

The front bulkhead comprises a steel eggbox construction, with diaphragm rings and ribs for extra stiffness, and contains a support frame for the screw conveyor and gate, cutter drive unit and other components.

The forward screw conveyor gate is itself fabricated to very tight tolerances, enabling the cutting head chamber to be isolated and pressure maintained, during maintenance operations.

There are also working platforms, within the TBM and cantilevered behind, which allow access during erection of the tunnel lining and to manlocks mounted on the bulkhead.

The forward shield and middle body are articulated with the tailskin, to enable the 11.3m-long machine to negotiate curves on the drive; alignment of the TBM steering is monitored using lasers set up behind the machine.

The TBM components were supplied to Kawasaki Heavy Industries for assembly and testing, complete with the 95m long backup system, which is towed behind.

The machines are now being employed on the CTRL project, where they are exceeding the anticipated progress rates.

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