For a $29.5M civil engineering contract, Galliford Try's bridges project for Network Rail has a lot going on.
A new bridge has been slid over a canal, a very wide steel overbridge has been placed across a busy road, and a new concrete road crossing lifted in.
Assorted bored and driven piles have been required. A cofferdam has sealed the canal bank, roads have been rebuilt, and utilities moved on a large scale. Some 30,000m 3 of spoil has been removed for cuttings, and extensive soil nailing has been used to stabilise 60¦ slopes.
'And most of this is in residential areas, ' says Network Rail project supervisor Roger Colton. Some houses had to be bought for demolition or to allow work in their gardens. And the contractor has had to keep local roads open and traffic flowing from the start of work in January last year to August this year.
The tightly organised job is part of the $690M, 30km long Trent Valley four-tracking of the West Coast Main Line north of Birmingham. The existing two-track section has been a significant bottleneck.
'The work will mean 12 seconds off the journey time to Manchester and Glasgow, ' laughs Colton. More seriously, he adds that additional lines will increase capacity, not just for 120mph Virgin Pendolinos, but for stopping trains and freight.
A number of major blockades of up to 10 days in duration, but mostly between 36 and 54 hours, gave the space for critical work on the lines with lineside preparation and finishing limited otherwise to daytimes.
Biggest of the Galliford bridges and now mostly complete is a 24m span steel trough structure in the middle of the 1.6km long contract.
Here the rail is on embankment, passing over a busy local road.
The 18m wide bridge had to be built to one side, for later sliding, but tightly packed housing meant the only space was across the road.
'We had to make a trestle, with enough clearance to keep the traffic flowing beneath. We were virtually in the gardens and two houses were taken over to make space, ' says Galliford Try contracts manager Paul Howells.
The 5m high trestle needed temporary piling to support the steel and concrete composite structure above; this comprised three 2m deep steel main beams with six steel lattice beams across and then the C40/50 concrete deck.
'Steel was fabricated in Scotland and brought in piecemeal for bolting, ' says Howells. One of the trickiest jobs was threading dense rebar for the concrete deck.
Subcontractor Rock & Alluvium, part of Galliford, meanwhile continued work with permanent piles to widen out the abutments, installing some 200 CFA piles up to 13m deep through local mudstones, to allow embankment widening.
Network Rail took advantage of the changes to raise the rail height by 800mm but this meant putting additional load on the existing abutment toes.
'We worked out a solution using lightweight concrete blocks to replace the top 2m of the embankment, ' explains Colton.
The bridge was moved during a 10-day blockade, on two 32axle low loaders from Abnormal Load Engineering. This created further complications: the road dips and the carriageway had to be built up an extra 500mm to even out the gradient.
But this meant another problem. A 1,000t crane was needed for the installation, to lift in four 70t precast concrete sills.
A piece of waste ground near the bridge allowed the crane to sit just within lift radius but the built-up road edge was too steep for the crane.
'We had to put it there beforehand, build up the road and then remove the higher carriageway afterwards, ' says Howells.
Even so the operation went well, taking just two days of the overall blockade. The rest was needed for follow on trackwork and power lines.
Further along the line, two parallel bridges take the railway across the Trent & Mersey Canal.
One was big enough to carry twin rather than single track but the other needed replacing, again in steel for the 7m wide, 22m span. Track alignment ruled out moving the two existing tracks onto the stronger bridge so again a slide was needed ? this time within a PTFE lined steel trough resting on concrete beams.
A 20m long cofferdam was needed in the canal to create the abutment foundations and support temporary works; British Waterways gave permission but narrow boats still had to pass, especially at Christmas. 'You would be surprised how popular it is on Boxing Day, ' says Howells. Traffic lights were set up on the canal.
An 850t crane for lifting in sill units, this time only 35t each, was able to sit within an adjacent factory yard. Some 60 hours were used for the removal, the slide and demolition of the temporary works.
Work now continues on the final bridge, a 35m wide 24m span concrete road crossing.
Weekend possessions have been used here for lifting in 25t precast U-M beams. The biggest complication was building a temporary steel bypass bridge alongside. Piles up to 1.35m diameter were needed for that and the new bridge.
Client and supervisor: Network Rail Design consultant: Scott Wilson Main contractor: Galliford Try Piling subcontractors: Rock & Alluvium, Martello Piling Crane hire: Ainscough Precast concrete subconctractor: Macrete