Murphy Makes Light Work Of Bridge Replacement
Bridge replacement and track improvement projects are always complex, but none more so than when played out right within viewing distance of the general public from the comfort of their own homes. That was the task that faced us when carrying out the removal of a 140 year old railway bridge over Coombe Road at Norbiton, Kingston upon Thames (A238), and its replacement with a new 200 tonne structure, over the Easter bank holiday weekend.
The £2.5 million bridge replacement is part of a London-wide scheme by Network Rail to renew their older structures. Its completion allows trains to continue crossing it safely and provide smoother, more reliable journeys for passengers.
Coombe Road Bridge was originally opened 10 May 1869 and carries commuters between Shepperton and Waterloo and in a continual loop between Waterloo and Richmond, calling at Clapham Junction, Wimbledon, Norbiton, New Malden and Kingston in between. At the same time the underlying roads, including Coombe Road, 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, none more so than in such a built up residential environment.
This is where our months of design, planning, scheduling and project management, working with an array of manufacturers and sub-contractors, the local authority and Network Rail come in. The physical bridge replacement required four days of railway closure; the only opportunities available are Christmas and Easter holiday periods.
The Old Lady
The rail bridge replacement was originally planned by Network Rail to take place over the August Bank Holiday in 2008. An existing 42” Victorian cast iron water main owned by Thames Water – and affectionately known as ‘The Old Lady’ delayed the project. Running under the length of Coombe Road, it was feared the bridge replacement vehicle loads would place additional pressure on an already fragile pipe.
After months of detailed technical analysis, we came up with a different methodology for approaching the bridge replacement which was accepted by Thames Water. Instead of assembling the new bridge deck alongside the existing bridge and manouvering it into position using multi-axle transporters, we were obliged to install the bridge deck in component form using a 500t crane set up in a precise position in a residential road.
The route for the moving of heavy loads was restricted such that at no time was the water main crossed.
Key roads were closed and traffic re-routed on 22 March which gave us time to bring in all the necessary materials and bridge deck components to our compound. including 21t excavators, cranes, 300 tonnes of bagged materials for the backfill and new track ballast and seven trailers of pre-cast concrete cill beams and ballast walls.
The site is located in a densely populated area with houses either side of the road where the plant and materials were stored ready for use over the weekend.
Thursday 1st April
By 8.00pm Thursday evening, 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 line took place at 00.30 hours Friday morning after the last train had passed through, and Network Rail’s track team began the job of taking up 60m of track ready for handover to us for the next stage of the work at 6.30am Good Friday.
Friday morning saw the start of the original bridge dismantling and demolition. Having removed the track timbers, the wrought iron cross girders were burned out and lifted into trucks for disposal off site. Then the main girders were lifted out, each one 26 metres long and weighing 19t, and loaded away. We then began the task of demolishing the brickwork abutments and wing walls down to the correct level. More than 450t of demolition arisings were taken away.
By Friday night, the six pre-cast concrete cills 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 position 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. Also as the bridge sits at a severe skew, some 67° angle 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 tight tolerance. The cill beams were then secured to the abutments with vertical anchors cored through the abutments.
By 9.00am Saturday morning we were ready to install the main girders – each one 26m long and weighing 52t. By midday the crane had placed the first girder onto the cill beams successfully. 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. This enabled us to install the pre-cast ballast walls to provide a retaining wall for the backfill and ballast.
By 9.00pm the bridge deck was being fully bolted up and waterproofed.
On the day when the majority of the British nation was tucking into Easter treats, our team was hard at work installing the drainage, completing the backfilling and waterproofing. The track ballast was then lifted up onto track level ready for distribution and compacting to pre-agreed levels.
With our elements of the project largely complete, it was time to 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 our crane was utilised to lift off six pre-fabricated sections of new track in preparation for installation. The team then put down the panels, aligned and levelled them, and distributed and spread the track ballast.
Tuesday 6th April
The replacement is essentially complete, welcoming the first train of the day at 5.30am. The package of work was completed several hours ahead of schedule with great success, and no accidents or incidents.
It is a complex job to demolish a bridge and install a new one, especially in a built-up area and on a line which is used by so many trains. It would be impossible to carry out an engineering job of this scale without some level of disruption.
The roads remained closed until Thursday 15th April, allowing the plant and materials to be removed and the area handed back to the local residents.
All reasonable measures were taken to minimise disruption from noise and the noise levels were constantly monitored.
Over 700 local residents and businesses were fully informed of the planned programmed for the works. This was achieved via a public meeting held in December 2009 and a series of newsletters at the start of this year.
As with any job of this nature we took all reasonable steps to keep the impact of the work for the community and the travelling public to an absolute minimum.
Many local residents were very interested in the ongoing work over the weekend, and comments received were wholly positive – many even stopping to watch our progress and take their own 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.
Our thanks to the entire team who worked hard over a continual 100 hour period over Easter Weekend, and in the run up to the project’s start.
This includes 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.