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Polystyrene makes light work of new railway embankment

CONTRACTS

HUNDREDS OF polystyrene blocks have been used to form an embankment for a new rail line at Nuneaton Station in the West Midlands.

The novel method was specified by project designer Owen Williams Railways as part of the modernisation of the West Coast Main Line (WCML). Lightweight expanded polystyrene blocks has been used extensively on highways since 1972, but very rarely in the rail sector.

Owen Williams Railways, in partnership with subconsultant Bullen, recommended the blocks to overcome numerous problems on site.

Ground investigations revealed weak made ground prone to settlement. Improvement techniques such as stone columns could have damaged a buried masonry bridge taking the River Anker beneath the station, but the bridge still had to withstand the weight of the new earthworks.

The team suggested using stone columns away from the bridge, with modular blocks of high-density expanded polystyrene (EPS) used for the embankment supporting the new line, as an alternative to underpinning the bridge foundations.

The blocks weigh about 3% of traditional fill materials. Their closed-cell structure inhibits water absorption and they are unaffected by climate changes and immune to insect, bacterial and fungal attack.

Network Rail accepted the proposal and work began with flat layers of porous concrete infill, a 75mm sand bed and protective membrane over the bridge deck.

EPS blocks were built up to four and a half blocks high in the centre, stepping down at the sides. The polystyrene embankment was covered with a granular fill to achieve the railway gradient and smooth side slopes. It was then covered with rabbit-proof mesh and topsoil to complete the landscaping.

Finally, on top of this new embankment, a 250mm thick concrete slab was cast to support the track construction and the poles carrying the overhead line system.

Meanwhile Keller Ground Engineering installed 3,600 stone columns, 10m deep and 1.2m diameter, to improve the weak ground away from the problematic bridge.

As part of the WCML regeneration, Nuneaton Station is undergoing remodelling that will see construction of a new island platform and tracks.

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