The new facility includes the construction of a floating concrete platform 240m long by 28m wide in plan and up to 5m deep, with a draft of approximately 3m. The platform is formed from four equal sized pontoons laid end to end, joined by steel hinge systems and secured in the River Mersey by eight 2m diameter rock-socketed steel piles designed to allow the pontoons to move with the 10m tidal range of the River Mersey. The platform provides a berthing face and moorings capable of mooring ships such as the ‘Queen Mary II’. The new platform will also supports a reception building, pilot boat building, covered walkway and a full turning circle for coaches collecting sight-seeing passengers.

Originally, the client for the project, Liverpool City Council, had specified a concept which was based on a traditional steel pontoon design. Consultant Gifford and contractor Balfour Beatty were awarded the £18m design and build contract on the basis of their alternative proposal of concrete pontoons. Concrete construction offers significant durability, maintenance and cost benefits over a steel version.

Various locations were considered for the construction of the pontoons including a slipway at the Cammell Laird yard across the River Mersey. But in conjunction with the contractor’s temporary works team, construction of the pontoons on a slipway was discounted. Gifford design project manager Nick Clarke explained, ‘One of the major risks would be trying to get the completed units down the slipway and launched.The building of them isn’t really the issue, it was all about how you mobilise these 3,000 ton lumps of concrete and what happens to them when they hit the water.’

In the end the team decided the best option would be to build the pontoons in a dry dock which could then be flooded, allowing much greater control over the way the massive structures will enter the water.

The pontoons are essentially being constructed using flat slab techniques with a 230mm thick external wall all the way around the outside of each pontoon. Internally the structure is divided into individual cells by walls as thin as 150mm. It is a traditional structure in terms of shuttering and placing concrete but it is heavily reinforced to cope with the loading expected from both berthing cruise liners and environmental conditions.

The new cruise liner facility should be complete in time for the lucrative summer season this year and will host the celebrations for the 40^th birthday of Cunard’s Queen Elizabeth 2 liner on 21 September.

MJ Information No: 22706