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Practical packaging gets the Rugeley by pass built

ROADS AND BRIDGES - Funding and technical issues made it necessary for Staffordshire County Council to split the Rugeley bypass into three phases. Alasdair Reisner discovers how the council went about getting the best team for each job

TO LOSE one major employer in a town is evidently difficult for its residents. But back in the 1990s the town of Rugeley in Staffordshire was hit by a double whammy. Within five years both the colliery and one of the town's two power stations closed down, resulting in high local unemployment. Staffordshire County Council realised it would have to sort out the town's transport system to breathe new life into its economy.

'The Rugeley bypass became the focus of attempts to try to recover from some of the town's problems, ' says David Barker, the council's project manager for the scheme.

Things got off to a good start when, in 1997, the first stage of the bypass was built using money from European regeneration grants and English Partnerships.

But since then the council has been toiling away to prise the money out of the Government to complete the job. This was finally achieved in 2004, giving the council the green light to get the project under way.

But there was a snag. As is often the case with such decisions, this funding came with conditions attached. One of these was that the council had to get the show on the road almost immediately. While this was exactly what the council wanted to do, it didn't take a civil engineering expert to realise that you couldn't just design and procure a £22 million project overnight. The planned completion of the bypass would require it to pass under railway lines and across a f lood plain, so it required a great deal of planning before the major ity of works could begin on site.

The council took a pragmatic approach.

'The only way to do it was to split it into parts. We determined that having three separate contracts would be sensible, ' says Mike Smith, the council's resident engineer for contracts one and two.

The first contract (see below) was deliberately kept under the £3.8 million threshold set by the European Union, above which it would have had to be put out to competitive bidding. By doing this the council was able to draft in its framework partner, Wrekin, to do the work immediately, saving a huge amount of time while still being able to work with a firm that it knew and trusted to do a good job.

The rest of the works could then simply have been boxed off in a single contract. But the council knew that if they did this the work would only be available to those firms that could handle the two tricky rail bridges that were needed. Rather than limit its options the council split the work into two. The two rail bridges, which would require close working with Network Rail and the nearby power stat ion, were packaged up as Cont ract 2, along with construction of a 600 m stretch of road between them.

Contract 3 was everything that was left over;

a 2.2 km road across the flood plain with three structures over the River Trent and the Trent and Mersey Canal.

Following the completion of Contract 1 earlier this summer the majority of effort on site is currently associated with Birse's work on Contract 2, where things are proceeding at a healthy pace, both on schedule and on budget.

So how did the firm find itself winning the work in the first place?

It all came down to Birse's track record, both for bringing innovative solutions to rail projects and for working in partnership with its clients.

Mr Barker recalls: 'I suppose it came down to experience. Birse Rail had significant work with Network Rail so that put them in a very good position. They grasped the principals of the job had a good understanding of the technical difficulties outlined in the tender document.'

The project was tendered with an eye on getting the best work rather than the lowest price, with an 80/20 quality/price ratio for bid evaluation and an emphasis on partnership working.

Birse had worked with the council when it became the first local authority ever to let a major highways contract as a partnership deal (the 1996 Tunstall Western Bypass), so the contractor was in a good position to demonstrate that it could work in this manner.

'We have achieved more certainty of outcome for the community as a result of our contract strategy. I am not aware of any outstanding claims on any project with the par tner ing approach we have adopted , ' says Mr Barker.

The job was awarded to a joint team of Birse Rail and Birse CL in October last year and work started on site in January.

One part of Birse's bid that impressed the council at the tender stage was its desire to tear up the existing designs for the rail bridge carrying trains between Rugeley and nearby Cannock. Instead of taking on the planned option of piled abutments for the bridge, Birse suggested an alternative; building a much larger bridge off-line and sliding it into position during a closure.

'That brought savings through building both bridges in a similar fashion. The first, which serves the power station, was already planned as a push but by using the same method for the second bridge the skills, equipment and temporary works all became common to both jobs, ' says Stuart MacFarlane, Birse Rail's agent on the job.

But before either bridge could be built and slid into place excavation was required to create a platform for their construction. Working so close to the river Trent, this presented an n See page 41 obvious problem; the ground water level was higher than the level at which the team would be working.

'We had to put in a dewatering system throughout the site to lower the water level by about 1.5 m, ' says Mr MacFarlane.

At tender stage the team estimated this would require up to 18 boreholes to be sunk down to 18 m below the site, all linked by a ring main. This system would pull water through the sands and gravels and pump it from underneath the working area and out into existing culverts and drainage systems, keeping the site dry.

When the team carried out test bores they estimated that actually only 10 boreholes would be required. It seems their sums have been proved cor rect as these 10 boreholes, pumping continuously 24 hours a day for six months, have been successful in keeping the water level down throughout the construction phase.

'If they were not there the site workers would be under water, ' smiles Mr MacFarlane.

With the site dry, the team excavated the casting basins in which the bridges would be constructed.

'The bridge is a reinforced concrete structure built in situ on a blinding layer covered with a separate membrane of polythene.

Once the br idge is built we have to jack it up and slide it, so we need it to come off the base it is being constructed on, ' says Mr McFarlane.

Gary Wilde, Birse's project manager for the bypass explains how the slide works.

'Temporary steel beams are installed through openings in the bridge abutment so the permanent works of the abutment helps carry some of the bridge's weight. Prior to the slide heavy moving specialist Mammoet comes in and puts the slide track down. Basically it's a steel track on top of precast units that we have put down. They put in the jacks, which are connected to a power pack, under each beam. There is a hydraulic push-pull to give the horizontal impetus.'

'Once the vertical jacks have lifted the bridge up this horizontal ram gets a reaction off the weight of the bridge. It pushes itself against a side track , moving the br idge along, ' says Mr Wilde.

The jacks have stainless steel on their base and sit on Teflon pads on the base of the slide track, giving a very low friction coeff icient. It is estimated th is should be 10 per cent of the dead weight for the horizontal reaction but at Rugeley it turned out that they had a particularly good slide track, requiring just 5 per cent.

The br idge pushes were both car r ied out during possessions of the railway tracks. In the case of the first bridge this was relatively simple as the tracks in question serving the power station were out of use for 16 days while the facility carried out a planned summer shutdown. But the line between Cannock and Rugeley that the second bridge would be slid underneath was in daily use. The project team negotiated with Network Rail for an eight-day possession, in which it was vital all of the works were carried out. No problem, according to Mr MacFarlane.

'During the eight days we excavated 20,000 cu m from the embankment carrying the railway, moved the 5,500-tonne bridge 90 m and backfilled with approximately 8,000 cu m of material. The slide itself took about 10 hours at nine or 10 metres an hour and we then reinstated and handed back the railway at line speed, two hours and 10 minutes early, ' he says.

In order to ensure that the movement of the bridges didn't do damage to their structure the team installed bracing and ties to the first br idge to keep every thing in place.

'The second larger bridge had a lot of reinforcement in it, most of which was required for the move itself, rather than for its permanent condition, ' says Mr Wilde.

To prevent any lateral loading in the 550-tonne bridge deck it was isolated from the rest of the structure, essentially floating above the abutments on a system of temporary bearings - jacks sitting on grease plates. This allowed any movement in the deck relat ive to the rest of the bridge to be corrected , so when the slide was completed the deck was exactly where the team wanted it to be, with in tolerances of 20 mm and 50 mm from the embankment at either end.

With the two bridges now in place the team could get to work building the road that links them. But again, the Trent f lood plain posed a problem.

Mr Wilde says: 'We would not normally build below the flood level but in this instance it would be very difficult to raise the railway line such a short distance from the nearby West Coast Main Line. As a consequence the road had to go under the railway so there was a need to protect it from flooding.'

This has been achieved by building the road in a reinforced concrete U-shaped trough. The initial design had specified a large mass concrete slab for the job but the new design uses far less concrete. It features a 200 mm base slab sitting on a bentonite blanket that acts a waterproofing membrane. General fill is then put in the t rough to counteract the buoyancy.

'It is about 16 m wide and runs about 300 m either side of the bridge. At maximum it is 1.5 m deep. A one-in-100 year flood will never get over the top of the walls. The only way it could get in is by leaking into the trough and the bentonite stops that. The mass inside it stops the whole thing floating off down to Lichf ield, ' says Mr Wilde.

The array of techniques that have been employed on the project show how the skills of the team have combined to build the Rugeley bypass. One client, two contractors, three contracts: formidable results.