The mitred lock gates are a critical part of the dry dock facility; enabling the Environment Agency to maintain its vessels adjacent to the navigable River Thames.
The gates retain a large volume of water upstream, and with personnel often working in the dry dock area behind the gates, maintenance of the gates and the surrounding civil structure is crucial for both functionality and safety. Environment Agency surveys determined that the previous timber gates had reached the end of their service life and needed to be replaced to maintain safe usage of the dry dock facility. ECS Engineering Services were then contracted to carry out the gate replacement work.
Steve Crapper, precontract director at ECS, said: “When assessing the Sunbury site, we saw an opportunity to use the latest material technology to replace the lock gates and provide the Environment Agency with a low-maintenance solution with exceptional service life and value.”
FRP technology and its core materials have been used industrially for decades across Europe. The specialised ‘InfraCore Inside’ manufacturing process, patented by FiberCore Europe, combines strength and integrity in an affordable material solution. Consisting of glass-fibre-reinforced polymers and a special thermosetting resin, FRP is layered for strength, durability and lightweight construction.
ECS installed an FRP bridge for the Environment Agency at Mapledurham Lock in 2016 and has been a leading user of the technology since. With FRP used already for large lock gates in the Netherlands, ECS took the opportunity to apply the technology to lock gates for the first time in the UK.
Crapper adds: “Thanks to tremendous longevity, FRP lock gates are essentially maintenance free - the lifespan of an FRP panel is at least 100 years. Timber gates would need structural maintenance within 10-15 years, while steel gates require a full repaint with an anti-corrosion coating every 15-20 years. This excludes any ad-hoc repairs that may be needed.
FRP is stronger than steel, wood and concrete. Furthermore, FRP offers a lower CO2 footprint due to improved material sustainability - an important factor for all infrastructure development projects. Each FRP lock gate is prefabricated, which speeds up the installation process and minimises work on-site. The material is also inherently fire resistant.
Each of the two replacement FRP gates measures 4m high x 4.5m wide and has a mass of approximately 10 tonnes.
David Searle, operations manager at ECS, said: “FRP gates can be designed to be lighter than timber and significantly lighter than steel alternatives. This lightness means that operating forces to open and close gates are reduced, which results in less energy consumption. Another benefit is less wear on components such as bearings, along with reduced strain on the surrounding dock chamber structure. The Sunbury gate design also enabled the existing hydraulic control system to be retained.”
All steel components below the water line were manufactured in stainless steel, with the brackets supporting the walkway produced from more economical galvanised steel. The use of stainless steel extended to the hydraulically operated sluice gate and mounting frame, with low-maintenance modern bearing materials deployed on the bottom pintle and top hinge. The civil infrastructure at the site has also been comprehensively overhauled. Every aspect of the design has been optimised to deliver maximum possible service life of the dry dock.
“FRP is a highly advanced and beneficial material for use in lock gates for the UK’s inland waterways. As the maintenance of existing structures becomes a bigger portion of their overall cost and environmental impact, a low-maintenance, durable material solution, such as FRP, offers great advantages,” Crapper concludes.
