The horizontal component of the thrust force is taken by four vertical slip bearings which are inserted into slots cored through the four wing walls.
These bearings prevent the arch from spreading horizontally, while allowing vertical movement. Once they have been grouted in place, it is safe to wire saw cut the rest of the wing walls to free the arch from the foundations - then the lifting can begin.
The lift took place in October 2016. Computer-controlled jacks provided a fully balanced, synchronous lift, as the 160-year-old, 220 tonne bridge was jacked 900mm.
As the jacks lifted, hardwood timber crib stacks were inserted beneath to support the bridge each time the jack foot retracted.
The lift took about six hours, during which constant monitoring verified that the arch was behaving as predicted.
The arch was then lowered by 465mm so that re-profiling of the approach ramps was unnecessary.
The bridge was left 435mm higher than its starting position and the gap in the abutment was faced with brickwork and flooded with concrete to restore permanent support.
The main engineering challenge in this project has been conveying the project in ways that other engineers and clients can understand.
Perhaps the hardest thing is to explain that, in modern terms, these bridges really aren’t that heavy. You could hire a crane and lift the whole bridge out in a piece with a little planning.
In some ways Elevarch would have been better understood and accepted by medieval masons than modern engineers.
Modern design rules, even for masonry, are fixated on modern engineering concepts, particularly analysis – it has rather fallen from favour to think that you need to explore the boundaries of possible behaviour to be confident the work is OK.
Elevarch has potential for much wider application: both applied to canal bridges, and as an alternative to demolishing bridges that are no longer wanted: when arches are demolished, they are usually broken out and dropped on the track – by lifting them out a huge amount of railway stoppage time would be saved.
We hope to see the solution rolled out across the UK and in other countries, and we are delighted to have won the Structural Award for Outstanding Value.