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News & Media > Rail Services

04:02:2010

AVOIDing future problems

May Gurney is nearing completion of a £395,000 project to infill voids at Beacon Hill Viaduct in Halifax, to ensure that the structure remains as strong as it appears.

Beacon Hill is a gritty example of a Victorian stone viaduct apparently built to last - but the solid edifice conceals a series of voids built into the viaduct just below track level and posing a risk of potential future failure.

These voids are an original construction feature and were included for good reason. They lowered construction cost by reducing the volume of stone to be quarried, transported, shaped and installed. They had further beneficial effect by reducing the load applied to the foundations.

Network Rail’s LNE route commissioned a programme of investigations to assess the risk of void failures and instigate works to reduce this risk.

The repair project was passed to May Gurney under the LNE Territory Structures Framework. The detailed design was developed by May Gurney’s in-house design team, based in York, and entailed filling the spandrel and king pier voids with foamed concrete.

The viaduct is on the Halifax to Bradford section of the Caldervale line and sees a regular succession of trains during the day. Works had to be designed to keep trains moving and this precluded extensive works from track level - the easiest route to reach the spandrel voids.

Just as with the earlier investigations, the only way to gain access to the voids was by coring. Holes 100mm diameter were drilled diagonally upwards from the arch barrel into each of the spandrel voids. On the opposite side of the void, a 50mm diameter hole was cored to act as a breather hole.

The lightweight foamed concrete had a density of around 1200kg/m3, around half that of normal concrete. This minimised the additional load being placed on the structure and its foundation. It also meant that no special consideration was needed in sequencing the pours as the additional weight would not destabilise the adjacent arches.

From the initial coring investigations to pumping the foamed concrete, the majority of work was carried out on mobile elevating work platforms.

The viaduct is a Grade II listed structure so care and thought went into minimising the intrusion of the works on the appearance.

From start to finish, the operation has been the structures equivalent of keyhole surgery, from the initial endoscopic investigations to the final verification of concrete levels.

Works were completed over an eight-week period during November and December 2009, and the outcome is a viaduct as solid inside as it appears from the outside.

Click here to read the full feature length article, courtesy of The Rail Engineer.

Click here to read more about May Gurney's work in partnership with Network Rail.