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Fast slab lifting without disruption

Settlement to base slabs which threatened to disrupt operations at a rail depot in Farnham last autumn was quickly dealt with by the use of polymer injection from specialist contractor Uretek UK Ltd.

The 60-year old slabs had been gradually settling for many years, due to compaction of fill material, drainage and washout problems, and the increased weight of modern rolling stock.

The problem was mitigated with speed restrictions, but had reached a point where further use of the 6000-sq-metre facility was jeapordised, with consequent disruption to railway timetables.

A piling solution was rejected due to cost, while breaking out and replacing the slabs was thought too time-consuming and disruptive. Adding ballast was also considered, but as it would not provide a long-term solution, was passed over in favour of polymer injection.

The Uretek process involves inserting copper pipes through narrow-diameter holes and then injecting fast-expanding polymers which fill voids, consolidate the ground, and then provide lift where necessary. Highly controllable and with a design life in excess of 100 years, the process is very fast to apply, with 90% strength being achieved within 15 minutes. Polymer injection was pioneered by Uretek 30 years ago in Finland, and is nowadays used throughout the world for a wide range of ground improvement.

Uretek teams began work at the Farnham facility on 22 November, and finished on 16 December. Operations of the depot were not disrupted during the repair, and tolerances well within the +/- 10mm target were achieved. 

The project was carried out by Network Rail, Osborne Rail and Uretek working in partnership, with support from Frankham Consultancy Group.