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News Release from: DavyMarkham | Subject: Cutter head fabrication
Edited by the Manufacturingtalk Editorial
Team on 09 April 2007
Largest hard rock tunnel boring machine
To serve a Niagara hydro-electric project, DavyMarkham manufactured a cutter head support and a final drive housing for what is claimed to be world's largest hard rock TBM (tunnel boring machine).
Sheffield engineering company DavyMarkham has produced the giant cutter head support and final drive housing support for what is believed to be world's largest hard rock TBM (tunnel boring machine), to be deployed on a landmark Niagara Falls hydroelectric project The GBP1/2 million contract was placed by the Robbins company of Ohio, a leader in the design and manufacture of TBMs and underground excavation equipment, with whom DavyMarkham has a long-standing business association, dating back to the joint venture production of two marine running TBMs for the Channel Tunnel, itself dubbed 'The project of the Century'
This article was originally published on Manufacturingtalk on 10 Jul 2008 at 8.00am (UK)
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Last year, Canadian hydroelectric company Ontario Power Generation announced the appointment of major European construction company, Strabag AG of Austria, to build a 10.4 kilometre (6.4 mile) hydro tunnel stretching under the world famous city of Niagara Falls, from the upper Niagara River to the Sir Adam Beck power stations at Queenston.
Running parallel to the two existing water tunnels, built during the 1920's and 1950's, it will reach a maximum depth of 140 metres (459 ft) and will be one of the largest tunnels ever built in North America.
During construction an estimated total of 1.6 million cubic metres of rock will be removed and, upon completion, it will increase the Beck power generating capacity by 1.6 billion kilowatt hours per year, sufficient to supply 160,000 extra homes.
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Strabag AG is using the specially-designed Robbins TBM to bore a tunnel of 12.5m finished diameter; uniquely, the machine was assembled on site to reduce overall construction costs and meet the project's tight delivery schedule.
Recently christened 'Big Becky', the open, hard rock TBM will incorporate Robbins' proven floating gripper design and the cutter head will be powered by a 4,725kW variable frequency drive system, expandable to 5,040kW.
The machine's average advance rate is around 12-15 metres a day, with the spoil likely to be used by Ontario's clay brick industry.
DavyMarkham supplied the cutter head support and final drive housing, which bolt together to form the TBM's front-end drive module housing and carry Robbins' 500mm (20inch) cutters.
In addition to collaborating on the 8.4m diameter Channel Tunnel machines, which proved to be the fastest TBMs on the whole project, the Sheffield company has previously worked with Robbins on such diverse tunnelling projects as Boston's 'Big Dig' highway tunnel, a 10m TBM for the Manapouri underground power station in New Zealand, the Lesotho highlands water scheme in Southern Africa and the New York Queens subway tunnel.
For the Niagara tunnel project, DavyMarkham manufactured a cutter head support fabrication measuring approximately 7.2m in diameter, 1,200mm deep and weighing 85 tonnes, and a final drive housing of the same diameter, which is 1,100mm deep and weighs 44 tonnes.
The cutter head support houses the 15 motors/gearboxes that continuously rotate the cutting tools at relatively low rpm, breaking the rock face into chips that are collected in a rear-mounted chamber.
The final drive housing carries the main bearing, to which the cutterhead adaptor is fitted, and is sealed internally and externally to prevent the ingress of dirt or water, with galleries through the fabrication for routine oil lubrication.
Steel plate in thicknesses up to 150mm was used for both units, which required 1,300 machining hours and 6,700 man hours in total.
Semi-automatic MIG welding was used for the fabrications, which were fully stress relieved before machining on DavyMarkham's large vertical and horizontal borers, then non-destructive tested using ultrasonic and magnetic methods.
Delivery of the finished components was direct to Niagara Falls, in line with Robbins' on-site assembly techniques.
Tunnelling work is currently progressing on schedule, with new, clean electricity expected to be produced by late 2009.
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