It is estimated that 500 masonry arch bridges in the UK are too low for Network Rail’s electrification programme. A cost-effective solution is required to avoid the demolition of hundreds of overbridges. In 2014, Freyssinet took part in RSSB’s Avoidance of Bridge Reconstruction competition joining forces with masonry arch expert, Bill Harvey, to explore the feasibility of vertically jacking bridge arches. The resulting ElevArch® concept was selected as one of four to advance into phase two of the competition - the full-scale demonstrator. This cutting-edge technique and sustainable solution for jacking rail masonry arch structures avoids unnecessary demolition and reconstruction for electrification schemes throughout the UK.
The novel ElevArch system was conceived in response to a competition to develop an economic and sustainable solution for raising masonry arch bridges over rail lines, that would avoid unnecessary demolition and reconstruction throughout the country.
Last year, a suitable bridge was identified; the 160-year-old, 220 tonne bridge at Moco Farm in Buckinghamshire. The arch was saw-cut at the abutments and then successfully raised up to 900mm over a matter of hours with ten fifty-tonne jacks, before being re-set at the required level. This operation could occur over a single night’s rail possession and the direct costs are expected to be significantly less than reconstruction or track lowering alternatives.
The judges were impressed by the potential of this idea, which solves the significant logistical problems associated with increased height requirements on rail lines. The carefully developed system and sequencing provides continuous restraint and support to the masonry arch through a series of jacks and vertical slip bearings inserted in key locations cored into the masonry bridge. The lifting operation was carried out after wire saw cutting the arch – with the 50-tonne capacity jacks computer controlled from a central to an accuracy of 0.1mm to ensure a synchronous lift. Monitoring was carried out throughout the lift to verify the arch behaviour.
The final bridge position was 435mm higher than the original – permitting limited reprofiling of the approach ramps and supports reinstated by flooding joints with concrete.
The judges recognised this inventive system could only be realised with the engineers’ deep knowledge of masonry behaviour and lifting processes, and has the potential to extend the life of many bridges whilst dramatically reduce costs and disruption to rail services during electrification works.