RAIL SERVICES ROUNDUP

Injection waterproofing - a cost effective solution
Rail Services is deploying injection-waterproofing techniques as a cost effective method to repair, refurbish and reconstruct railway structures.

Rail Services first proposed this technique to Network Rail back in 2002 - to avoid total removal of the track and disruptive possessions that are associated with more traditional waterproofing processes.

At that time, Network Rail requested hard evidence that it was a workable solution. With this in mind, May Gurney applied the technology at a small masonry arch rail underbridge over a quarry access road near Leeds. At this particular site, water was pouring through the soffit of the arch, saturating the road below.

Rail Services, in conjunction with Network Rail, treated the project with a 'research and development' approach to prove the injection waterproofing process. Initially a matrix of cores were drilled into the bridge through which the chemical (manufactured in Germany) was injected. The process works by the chemical being pumped into the structure in equal parts with water that contains a powder accelerator controlling the adjustable set time (15 seconds to 15 minutes). As the constituents meet and mix they form a waterproof gel, which seeps over the extrados of the arch and into any cracks within a structure to seal them. At Leeds, the project was apparently 95% successful and the technology thereby appeared to be a more cost efficient way of waterproofing bridge decks.

Network Rail's engineers then selected a further masonry arch underbridge at Dewsbury to prove that the process could be consistently effective. Rail Services commenced work on the structure in December 2005.

The trials have highlighted that, in the first instance, masonry repairs need to be undertaken to ensure that any voids are initially filled with a structural grout. The gel is then injected and forms a waterproof flexible coating over the extrados of the masonry structure.

On another trial project, a steel deck underbridge near Grantham had a small number of deck waterproofing failures at the joints where the deck units were bolted together. Using traditional waterproofing remedies, possessions would have been required to lift the track, remove the ballast and the protective boards to the waterproofing to enable the repairs to be made - all very expensive and disruptive to the railway. A decision was made to inject the waterproofing gel into the joints and recent inspections have shown that the leaks have been successfully repaired, again at a low cost.

Injection waterproofing is a very cost-effective process. As an example to show potential savings, a traditional membrane waterproofing job, proposed for a three span arch on the ECML was estimated to cost in the region of £800k. With the line speed being 115 mph and the continuously welded track having a cant of 150mm, the risks associated with removing the track and ballast, waterproofing and re-instating - all within a 54hr possession - were enormous. A price has since been calculated for injection waterproofing from underneath the arches and this is in the region of 25% of the cost for laying a waterproof membrane under the track.

Since injection waterproofing is still a development system, prior to further schemes being selected for this system, Network Rail's engineers have requested that Rail Services prepare a report. This will be produced, in conjunction with the German materials supplier, for submission to Network Rail for formal 'Technical Approval'. Injection waterproofing has been used for some years on the continent, but if its effectiveness can be proven in the UK climate, this approach could offer substantial cost efficiencies for Network Rail.

Pitsea footbridge underway
Detailed planning is underway for a project to refurbish a passenger footbridge located at Pitsea Station in Essex, which will take place during March 2006.

The existing footbridge that is to be refurbished

May Gurney Rail Services has been commissioned by Network Rail to replace the existing spans of the footbridge, serving two platforms, as they have reached the end of their serviceable life. The existing supporting columns and staircases will be retained and re-used.

To ensure the project is delivered right first time, a detailed risk assessment exercise is preceding the works. This is to ensure that potential risks and contingency plans are prepared to effectively manage any issues arising. For example, it is possible that existing nut and bolt fittings on the iron bridge may have rusted into position over the years. If this is the case, before the redundant spans can be removed by crane, the bolts will need to be cut out and temporarily replaced to prevent delays on removal day.

As well as managing the logistics of lifting out the redundant bridge sections and craning in the new bridge, services running across the bridge, such as telecoms and CCTV cables, will also be identified and relocated. This activity will be managed during the 10 days of enabling works that precede the bridge installation. During this final phase, the project team will take two 27 hour railway closures over consecutive weekends, during which time a heavy mobile crane will be used to lift out the existing iron bridge, weighing an approximate 12.5 tonnes, and install the new section. C2C will provide alternative travel arrangements for rail passengers during this time.

The replacement span will be prefabricated steel, manufactured off site and delivered as one unit on the back of a lorry. The bridge will be precision lifted into place by the crane, which will be situated on the station forecourt. Detailed geotechnical investigations will take place well in advance to ensure that the ground will be able to bear the load of both the crane and bridge.

This bridge replacement project follows other works that May Gurney Rail Services has recently completed for Network Rail at Pitsea. In late 2005, the company completed the construction of a new station at Pitsea and the refurbishment of the local signal box. All the works are part of the East Anglia Property Framework Contract that May Gurney holds for Network Rail.