Unique fortification process for twin channel wailing beams

Authorship

Peter Bishop, BAM Nuttall Ltd., Camberley, UK

Publication

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Nuttall John Martin is currently working on a 330 metre length of the longest continuous quay wall in the UK at Trinity Deep Water Terminal, Berth 5. The remit is to strengthen the existing twin channel wailing beams in reinforced concrete.

This, as a normal exercise would not be something out of the ordinary, but on this occasion the existing beams placed at – 0.8 AOD (just above mean low water springs) are only visible in the 4 metre tidal range for an average of two hours either side of low water. The existing quay is a suspended deck onto King Piles with
fender blocks spaced along the quay. The works are part of the ongoing maintenance of the port facilities by the Port of Felixstowe.

Walkway spans

Site production on encasing has to reach 18 metres per week to enable the 330 m to be delivered in the 19 week availability of the existing quay. This has lead the team at NJM to design and develop a set of five combined access and shutter walkway spans to allow access and provision of the shutter to the waling beam. As further considerations to the client the team only occupy a rolling 72 metres of quay at any one time allowing the client to continue to access the remaining 258 metres.

The site team had to survey the original waling beam, fender blocks, king piles and location of the existing beams. This work was carried out by the site engineering team and used as the basis to design and manufacture the access and shutter walkway spans. As a testament to the accuracy obtained, once the spans were  assembled and installed, the survey work was proved to be successful with no modifications required.

Concrete mix

Further unique input into this scheme has been the site development of the concrete mix used for the process. Each single pour accounts for 4.5 m3 of site batched concrete with acombination of corrosion inhibitor, super plasticiser and accelerator. The ability to produce the concrete mix as and when needed for site operations has all added to the smooth production achieved to date. Concrete has to be able to be placed using a tremmie pipe and the mix has been designed to cope with being placed in the dry or tremmied if the tide overtakes the concrete pour. The C50 mix design has to achieve an initial strength of 12 N/mm2 within 12 hours, and 28 day strength is averaging 65 N/mm2. The engagement with client, engineer (Royal Haskoning) and the site team has led to the development of a revised reinforcement detail which means 90 per cent of the steel is fixed in the shutter prior to be lifted into place. This ensures consistent quality and less time in shutter preparation.

The unique access spans have been constructed as two left hand, two right hand and one standard access intermediate span. The single access span is used to prepare the section of beam to be concreted, jet washing marine growth, welding of rear back plate, the appropriately handed section then replaces the access platform and the front shutter and reinforcement and stop ends are positioned. The 4.5 m long section of shutter is washed out and concreted; this process has  normally been achieved on the second low tide from starting and then left for the fourth low tide to remove at the required minimum strength. By interplaying the left and right handed shutters (a function of the spacing’s of the fender blocks) progress is achieving a rate of 18 metres per week.

Unique solution

This unique solution was offered to and accepted by the client in a competitive tender situation, which was open to a mixture of the following elements, construction  ideas, budget, survey ability, cost effectiveness, design and a well engineered solution. The Nuttall John Martin team are proud to be able yet again to offer cost  effective unique solutions for the Port infrastructure sector.

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