Putting on an Easter show

Putting on an Easter show

28 Apr 2010

Bridge replacement and track improvement projects are always complex but none more so than when played out in front of residents sitting in their living rooms. That was the task faced by J Murphy & Sons over the Easter bank holiday weekend as it carried out the removal of a 140-year-old bridge over Coombe Road at Norbiton, Kingston upon Thames, replacing it with a new 200-tonne structure.

The £2.5 million project was part of a London-wide scheme by Network Rail to renew its older structures. Completion allows trains to continue crossing it safely and provide smoother, more reliable journeys for passengers.

Coombe Road Bridge was originally opened on 10th May 1869, carrying commuters between Shepperton and Waterloo, and in a continuous loop between Waterloo and Richmond. At the same time, the roads beneath it - including Coombe Road and Norbiton Avenue - are well used by commuters and local residents alike. As a result, a four-week road closure and four-day possession of the rail network was always going to cause some disruption and disturbance, particularly in such a built-up residential area.

This is where months of design, planning, scheduling and project management come in, working with an array of manufacturers and sub-contractors, the local authority and Network Rail. For the railway, the physical bridge replacement required a four-day closure - the only opportunities being the Christmas and Easter holiday periods.

The Old Lady

The bridge replacement was originally planned to take place over August Bank Holiday in 2008 but an existing 42" Victorian cast iron water main owned by Thames Water - affectionately known as ‘The Old Lady' - delayed the project. Running under the length of Coombe Road, it was feared that project vehicle loads would place additional pressure on an already fragile pipe.

After months of detailed technical analysis, a different methodology was established for the bridge replacement and this was accepted by Thames Water. Instead of assembling the new deck alongside the existing bridge and manoeuvring it into position using multi-axle transporters, it would be installed in component form using a 500t crane, set-up in a precise position on a residential road. The route for the moving of heavy loads was restricted such that the water main was never crossed.

Key roads were closed and traffic re-routed on 22nd March, giving the project team time to bring all the necessary materials and bridge deck components to the compound, including 21t excavators, cranes, 300 tonnes of bagged materials for the backfill and new track ballast, as well as seven trailers of pre-cast concrete cill beams and ballast walls. The site was located in a densely populated area with houses either side of the road. Here, the plant and materials were stored ready for use over the weekend.

Easter timeline

By 8:00pm on Thursday 1st April, an Ainscough 500t mobile crane and 135t of steel ballast for the counterweight were escorted in. The crane was rigged and ready to begin work shortly after midnight. Possession of the railway was secured at 00:30am after the last train had passed through. Network Rail's track team then began the job of taking up 60m of track ready for handover.

Friday morning saw the start of work to dismantle the original bridge. Having removed the track timbers, the wrought iron cross girders were burned out and lifted into trucks for disposal off-site. The main girders were taken out - each one 26m long and weighing 19t - and loaded away. The task of demolishing the brick abutments and wing walls down to the correct level then got underway. More than 450 tonnes of demolition material were removed.

That night, the six pre-cast concrete cill beams were ready to be brought round on trailers from their holding position to be within reach of the crane. One by one, they were lifted into place on the prepared tops of the abutments. This was a critical part of the project to ensure manufactured elements met the design criteria once in situ. As the bridge sits at a severe skew of 67° across the road, their positioning had to be precise so the bearing plinths were in the correct arrangement to receive the new girders. This was achieved with a ±10mm tolerance. The cill beams were then secured with vertical anchors cored through the abutments.

By 9:00am on Saturday morning, the team was ready to install the main girders. These weighed in at 52t and spanned 26m. By midday, the crane had successfully placed the first one onto the cill beams. The bridge deck had been pre-assembled on site, within reach of the crane, into six manageable sections. Weighing up to 45t, these sections were craned into position in sequence, enabling the pre-cast ballast walls to be installed, providing a retaining wall for the backfill and ballast. The bridge deck was being fully bolted up and waterproofed at 9:00pm.

When much of the nation was tucking into Easter Sunday treats, the team was hard at work installing the drainage, completing the backfilling and waterproofing. Ballast was then lifted up onto track level ready for distribution and compacting to agreed levels.

Easter Monday saw hand back to Network Rail's track team for the relaying of the track and placing the top level of ballast. An engineering train was brought in and the crane was used to lift off six pre-fabricated sections of new track in preparation for installation. The panels were then put down, aligned and levelled, and the track ballast distributed.

The replacement was essentially complete by Tuesday, welcoming the first train of the day at 5:30am. The package of work was successfully finished several hours ahead of schedule, without accident or incident.

Minimising the impact

With a job of such scale and complexity, it would have been impossible to undertake it without some level of disruption, particularly given the nature of the site and volume of traffic on the line crossing the bridge. The roads remained closed until Thursday 15th April, allowing plant and materials to be removed and the area given back to the community. All reasonable measures were taken to monitor and limit noise levels, and keep the wider impact on those living nearby and travelling public to a minimum.

Over 700 local people and businesses were kept fully informed of the planned programme courtesy of a public meeting held last December and a series of newsletters at the start of this year. There was considerable interest in the works over the Easter weekend and all comments were positive - many even stopped to watch progress and take photographs.

The project was a real team effort involving Murphy and its sub-contractors, designers, Kingston Council which had to approve the traffic diversions, and Network Rail's professional team. A huge amount of hard work was put in, not just over the 100-hour Easter weekend but also in the run-up. Amongst those worthy of thanks are Mott MacDonald, Cleveland Bridge UK, Ainscough Cranes, Marks Demolition, Kilnbridge, Waterseal, the Royal Borough of Kingston upon Thames, Thames Water and, of course, Network Rail and Southwest Trains.

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