Yonderberry Jetty is an HSE COMAH site jetty located in the Tamar Estuary and used for refuelling of tankers and lighter vessels; steel piles and RC deck with gravity fenders. The structure was constructed in the 1950s, and there were signs of corrosion to the existing piles. Constructex was initially commissioned to carry out a survey of the existing jetty and carry out a structural analysis before developing recommended pile strengthening repair solution. We then completed the installation of the repair solution.
The project required the analysis of inspection data (UT thickness readings) taken of the steel piles on this jetty structure in Plymouth Harbour. A detailed structural assessment was carried out by creating a structural model within Oasys GSA. Pile loss sensitivity, repair study on a case-by-case basis and an essential repair model. The outcome of the structural assessment was to determine a list of essential repairs required for the continued use of the jetty. In addition, revised berth loadings were determined for the continued safe use of the structure.
Following extensive inspection and structural analysis by Constructex, a repair scheme was developed which would give additional years of life to the jetty. The repair solution was steel repair plates: each plate was up to 6m long, and 12mm thick. A selection of plates were designed to suit the specific defect observed.
The plates required welding underwater, and were deigned to span over thinned and holed areas of the pile without any restraint benefit. The ends were rounded to reduce the concentration of stresses which were anticipated from the preliminary finite element analysis. The plates were fabricated with a fin plate to permit it to span the holed and thinned areas without additional restraint. A total of 38 plates individually weighing up to 150kg were installed by HSE Surface Supplied Welder/diver team over a 4 week period.
The works were carefully scheduled to avoid Spring tides where reduced visibility and increased strength of tidal flow prevented diver operation. The original programme was 6 weeks; this overran by 1 week due to unforeseen pile conditions leading to a compensation event. The contract price variation was approximately 5%.