In 2005 the Port of Liverpool’s largest dock entrance, Gladstone Lock, was severely damaged in a storm that ripped off one of the Lock’s 400 tonne mitre gates.
At the time, recovering and repairing the gate could have been a very expensive and lengthy procedure, but thanks to an innovative engineering solution developed by Royal HaskoningDHV and Mersey Docks and Harbour’s Chief Engineer, the gate has now been repaired and reinstated, and is spearheading an ongoing programme of refurbishment at the Port.
The 17m by 21m gate needed to be horizontal and in the dry to enable it to be repaired. The gate weighed some 400 tonnes and would have needed a large specialist lift crane from the Netherlands to lift it out of the water outright. The normal way of dealing with this would have been to float the gate into a dry dock and dry it out onto dock blocks. However, as the gate was damaged it was not thought to be stable enough to float it flat on its back as the gate had only been moved around using the MDHC floating crane holding it in a vertical position.
Our solution was to use the hollow gate’s natural buoyancy to offset most of its weight and build a special ‘tipping cradle’ to pull it into a horizontal position. The Port’s ‘Mersey Mammoth’, a 250 tonne floating crane barge, lifted the gate vertically while the cradle, attached to tugs by long ropes, started the tipping process, eventually pulling it through 90 degrees and onto dry land.
The gate was successfully refurbished and brought into line with current legislation before being reinstated using the same tipping cradle procedure but in reverse.
The renovation programme is continuing as work progresses on 40 similar mitre gates in Liverpool and along the Manchester Ship Canal. The amount of work has necessitated the building of a specialist refurbishment shed and the tipping cradle itself has been modified so that subsequent gates can be winched into the shed along a track and worked on under cover.
Working closely with Mersey Docks and Harbour we developed an ingenious solution to a potentially disastrous problem. The solution has since been improved to allow the client to consider confidently a much wider programme of renovation and refurbishment efficiently and cost-effectively.