As well as being the home of the Royal Navy, Portsmouth Harbour also houses an offshore ammunition facility. The critically-important jetty, located in the middle of the harbour, fits vessels with everything they need for battle – from missiles to bullets. The original facility, built in 1923, needed to be replaced as it was unable to support modern warships. A government's defence review identified Type 45 frigates, as a key component in the future defence strategy, so the Defence Infrastructure Organisation (DIO) contracted VolkerStevin, to design and build suitable offshore docking and loading facilities.
What we did
Located 800m offshore in Portsmouth Harbour, the new Upper Harbour Ammunition Facility (UHAF) was to consist of a jetty (15m by 85m), two mooring dolphins and two small vessel pontoons. We built the new jetty structure by driving forty-two, 40m-long tubular piles into the seabed, working from our floating crane barge. We then placed precast concrete pile caps, 28 precast concrete beams, and 14 fender panels. The structure was completed with in-situ concrete pours to stitch the units together and form the deck.
3,000 casting sockets were then placed into the pre-cast units to allow safe access, for scaffold and walkways to be set up as the works progressed. The facility did not have any land connection, so ensuring the safety of our employees and the safe transportation of machinery, equipment and materials was a key priority.
We redesigned aspects of the new structure to improve constructability and reduce safety and environmental risks. The pile design was then adjusted to eliminate raker piles, which would have presented major safety concerns due to the high tidal range.
The precast deck design was optimised by incorporating cable ducts into the in-situ concrete. We then made the deck a safer working space during construction by making it a closed structure. We also made the UHAF easier to operate and maintain, by flattening the deck and optimising the concrete mix to increase durability.
The value engineering initiatives we incorporated, allowed us to deliver the new UHAF structure one month early and on budget. The DIO Project Manager at the time, Paul Simmonds commented: "This has been a complex project due to the nature of the requirement, the environment and additional levels of regulation required for explosives facilities. The fact that the UHAF has been completed on time and within budget is testament to the excellent collaborative approach taken between VolkerStevin, the DIO and naval base staff.”
The two-ammunition handling cranes that we installed, meet strict military and explosive handling standards. We worked collaboratively with our specialist designer, Kenz Figee, and technical authority, Houlder, to satisfy the client and its competent assessor. We used lessons learned from the project to install two very similar cranes on a military jetty at Glen Mallan, Scotland.
We achieved a CEEQUAL ‘Very Good’ Whole Project Award—we avoided polluting the harbour and recycled 99% of waste when demolishing the old UHAF structure. Four wind turbines sustainably power the UHAF. The diesel generator is therefore only used bi-weekly during ammunitioning.
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