First traffic in three years crosses the High Level Bridge over the River Tyne
Surfacing Contractor: Tarmac National Contracting
Customer: Railtrack
Principal Contractor: May Gurney
Overall contract value: over £43m
Value of surfacing contract: £220K
Contract duration: commenced April 2001, completed 1 June 2008
Project Brief
To carry out a programme of remedial and structural conservation works for the High Level Bridge over the River Tyne. Work included the total replacement of the traffic deck used by pedestrians and vehicles.
Background
The High Level Bridge crosses the river Tyne between Newcastle and Gateshead and was constructed between 1846 and 1849 by Robert Stephenson (son of George Stephenson who invented the first steam locomotive 'the Rocket'), to carry trains for the York, Newcastle and Berwick Railway Company across the Tyne.
The bridge consists of two decks, with the upper exposed deck being for trains and the lower enclosed deck for pedestrians and vehicles. The bridge is a Grade 1 structure, which reflects its architectural significance, engineering quality and historical importance. Around 8,000 motorists a day used the bridge before it closed.
May Gurney was awarded the contract to carry out a programme of remedial and structural conservation works. However, once works commenced it became apparent that the scope of works would be far more extensive than first anticipated and the whole of the lower enclosed deck needed to be replaced.
Carrying out the work
The lower deck was constructed of cast iron beams, spanning from pier to pier. These beams had timbers bolted to them at 90 degrees to form the deck, which in turn was surfaced in tarmacadam to give a flexible running surface. The bridge's Grade 1 listing meant that these elements had to be replaced in line with the original construction.
More than 1,600 tonnes of scaffold were used in the project, which at any one time included more than 160 engineers and operatives, and 30 managers working 24 hours a day for 12 fortnights.
More than 75,000 litres of paint have restored the bridge to its original colour and 610 tonnes of new steel and 252 tonnes of new timber have been used.
The Challenges
The scope of Tarmac's work was to provide the asphalt surface to the enclosed lower deck. There were a number of issues which had to be overcome including; surfacing onto a timber deck, height restrictions and weight restrictions.
The original wooden deck had been fully replaced with 'Greenhear'’ timber from Indonesia. This particular type of wood is durable and has low permeability, which is ideal for a bridge deck. Only one other deck has been installed in such a way in the last 30 years. 252 tonnes of new timber were used on the project.
The initial specification was to provide a regulating layer of asphalt onto of the timber deck. A waterproofing membrane was then be sprayed onto this layer to protect the structure. This could not be applied directly to the timber decking due to the number of joints within the timber deck. A binder course of asphalt was then be laid onto the waterproof membrane prior to laying a hot rolled asphalt surface course with pre-coated chippings.
After careful consideration and consultation with the client, Tarmac proposed a number of changes to the initial pavement specification. The regulating and binder materials needed to be flexible due to the timber decking, yet had to be able to withstand the deformation stresses imposed by cars and slow moving, heavy vehicles like buses. Compaction was also an issue as the use of vibratory rollers was not possible on the bridge deck. The regulating and binder courses were designed in conjunction with Tarmac's technical team and Total Bitumen using Styrelf 15/60 bitumen.
The surface course was redesigned to use a 6mm Masterflex surface course instead of the hot rolled asphalt that had been initially specified. Masterflex provided a better solution due to the complex and sensitive nature of the project and the fact that there was no safe method of applying the pre coated chippings to the bridge's road surface. This was due to the restricted road width which would have meant all the chippings would have to be applied by hand resulting in operatives working in between the paver and rollers.
The bridge also had specific weight restrictions of 8.5t axel and 18t gross during the construction phase. Tarmac worked closely with the structural engineers on the project and agreed the type of paver and supply methods for each layer of the specification. A Dynapac F161 twin rear axel paver was used for all the laying operations, with the base and binder materials all being transported across the deck in 6t dumpers. The surface course was able to be delivered in heavier 16t wagons, as the increased depth of the deck's construction at that point gave a greater displacement of the loading from the axels.
All materials were supplied from Tarmac's Barrasford quarry in Northumberland.
Jim Beecham, senior contracts manager at Tarmac National Contracting said, "It's been a very exciting and challenging project to work on and it's a credit to all those who have been working on it. It's great to see traffic flowing once again over this iconic bridge".
Ian Carr, Area Technical Manager at Tarmac National Contracting said, "This was a very interesting project for all involved and it demanded a great deal of Team Work, not only within National Contracting but also all involved in the supply chain - principally Tarmac Northern and Total Bitumen"
David Sterry, May Gurney's chief executive, said, "With eight years of complex repairs to the High Level Bridge, we have demonstrated that cutting edge research can pay dividends - an extremely cost-effective solution involving a very high profile site."
For further information please Contact PR.
15 October 2008
