Poole Berth 3
Berth 3 is a Ro Ro berth operated by the port of Poole.
The berth is used by cross channel car ferries which
operate daily during the peak season. The berth is
constructed of Larssen sheet pile wall with a
reinforced concrete capping beam and slab. The sheet
piling is restrained by intermittent tie bars to a gravity
structure. There is granular fill behind the sheet piling.
At the end of the berth is a RoRo facility to allow
vehicle loading. The RoRo is built on two mass
concrete piers poured within permanent sheet pile
formwork. There is sheet piling spanning between the
piers below water level.
The RoRo sheet piling between the piers had become
badly degraded. It was suffering from corrosion
around the level of the tie bars. Many of the tie bars
had begun to fail, resulting in bowing out of the sheet piling in to the berthing pocket. There were concerns that continued degradation of the structure exacerbated by ferry prop wash could lead to failure.
Constructex were commissioned to carry out repairs on a design and build basis. The works took place over 2 years (2016 to 2017) as two individual contracts.
We developed a repair proposal which involved installing new tie bars and forming a reinforced concrete beam behind the sheet piling to restrain it. Ultrasonic thickness measurement of the existing sheet piling was undertaken to determine the best position to fix new tie bars. The tie bars were then installed by our dive team. These were fixed back to an existing strong point. Reinforcement cages were then fabricated and positioned behind the top of the bowed sheet piling. This was connected to every inpan and outpan using tie rod and custom fabricated washer plates to securely connect the RC beam to the sheet piling. Sandbags were used as an underwater formwork to constrain the pour. A marine concrete with Sika underwater antiwashout admixture was pumped to form the beam. This was installed using a tremmie method operated by our dive team. The total length of the repair was 12 metres with 40m³ of concrete poured.
The project was completed within a total of 6 weeks. The original programme was 5 weeks, however delays were incurred due to unforeseen ferry movements caused by poor weather and emergency ferry maintenance. The project spend over budget was 5%.