Refurbishment attention for Glasgow metro Aug 2012
Patrick Reynolds for TunnelTalk
Balvac, part of the Balfour Beatty group, beat out five others to win a second waterproofing and upgrade contract this year to refurbish deteriorated sections of Glasgow's twin-tube metro circle. The £1.3 million contract is to refurbish the 794m long concrete-lined section between Buchanan Street and Cowcaddens Stations (Fig 1).
Bids received by metro owner and operator Strathclyde Partnership for Transport (SPT), were assessed on a 60/40 weighting of quality to price. Balvac's bid ranked highest on quality and second lowest on price for the fixed elements as well as the variable elements of the contract. The contract specifies employing SPT permanent way equipment (locos, flatbeds) and manpower to complete work during night and non-operating engineering hours. SPT said this was considered the most economical way of doing the works.
Fig 1. Schematic map of Glasgow metro

Fig 1. Schematic map of Glasgow metro

Other bidders included Freysinnet Makers and QTS, which submitted an alternative bid.
Previously, Balvac won a £472,000 contract in March for waterproofing work between Kelvinhall and Partick Stations. Prior to that the firm also secured competitively a renewed five-year callout contract of £694,000 for water sealing works in the metro system.
The 10.5km metro circuit with 15 stations is 115 years old and was built entirely underground using various methods including cut and cover south of the River Clyde, cast iron below the river and under the River Kelvin, and bored, concrete-lined tunnelling on the north side. It is generally referred to as the world's third metro system after London and Budapest. In the late 1970s it underwent a major modernisation. No extensions are planed for the metro, which is constrained by its narrow track gauge of only 1.22m.
Balvac has been working on the metro since the early 1990s. In outlining its works on the metro since early 2011, including the Kelvinhall to Partick section, due to finish before the end of the year, Balvac said it has injected almost 40,000 litres of expanding polyurethane resin under low pressure behind the lining of the 3.35m diameter tunnels. It has also installed new track blocks and concrete drainage channel slips, cleaned more than 2.5km of central drainage, and undertaken various types of waterproofing depending on local conditions and type of lining.
Its latest contract calls for trial of a new two-part PU expanding resin when drilling through the lining to fill voids. This is expected to make for faster grouting. The Buchanan Street to Cowcaddens section has experienced some groundwater ingress and there is the potential of voids behind the lining.
Site investigation for the works was completed by Arup and included drilling through the lining and structural analysis of the lining. The groundwater levels are generally more of a challenge in the south side of the metro loop.
The refurbishment works contracts are re-measurable with allowances for unforeseen ground conditions and increase use of materials. SPT has allocated £2 million for tunnel lining works during the 2012-13 capital budget period, which is part of its £20 million-£25 million Revitalising the Subway Network over the next four to five years. Stations are also being upgraded in a rolling programme of refurbishment.
References
Dry approach to Connaught Tunnel repair - TunnelTalk, February 2012
High pressure refurbishment - TunnelTalk, August 2010

           

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