Brighton Palace Pier is a Grade II listed building that opened in 1899. The pier stem and head total approximately 540m in length and the pier head itself comprises structure from three distinct time periods. The central core comprises Victorian cast iron piles. To the north east corner is an area known as the boat deck built in the 1930’s. In the mid 1990’s the pier head was extended with new structure that surrounded the original pier head. The 36 piles to the 1930’s boat deck are rolled steel joists. Interestingly GTL’s initial involvement came from the fact that the original Victorian piles were screw piles.
GTL were commissioned to design, supply and install a piling solution for the boat deck replacement project. The clients engineer had originally planned to utilise helical piles, however, GTL were able to provide an alternative unique solution that would ensure build-ability and provide cost savings to the client. The new solution had never before been used in this environment and under such constraints anywhere in the UK.
Specific working restrictions made this particular project a challenge. The Pier itself is a commercially operating pier that attracts large numbers of public visitors. The design was developed to negate the need for access / working from the sea to reduce any potential delay due to poor weather and also mitigate potential health and safety hazards.
A structural working platform was constructed below the pier deck to enable access to install the piles. This obviously created working height, logistical and load restrictions; therefore, the
piles were designed in manageable sections.
Geotechnical Ground Conditions
GTL, in partnership with Whitworth Peck, reviewed the available soils data which revealed that the site was underlain by thin seabed gravels overlying Upper Chalk. The chalk was typically described as a very weak/weak low and medium density chalk. On this basis, GTL treated the chalk encountered as “rock chalk”.
The scheme required 24 bearing piles each consisting of a 406.4mm x 20mm thick circular hollow section installed in conjunction with a limited access segmental auger.
Compression loads varied, peaking at 1,300kN. In addition, there were significant shear and moment loads, with some minor tension loads.working platform was positioned 10m above the seabed and only 5m below the pier deck. The first pile section, 5m long, was placed within a specially designed piling gate and suspended above the sea while the other sections were connected via a flanged connection and lowered through the piling gate. This process was repeated until there was sufficient pile length to transfer the load from the working platform to the seabed. The CHS pile was then rotated into the chalk bed with a rotary piling rig
to a depth of 5m.
Additional sections were then added to achieve the designed embedment of the CHS pile. The centre of the CHS was then drilled out by a segmental auger piling rig and the pile was progressed to 15m design depth. The pile shaft was then grouted and the centre of the pile was reinforced with an Ischebeck bar.
GTL used Oasys software in particular ALP (Analysis of Laterally Loaded Piles) to predict the pressures, horizontal movements, shear forces and bending moments induced in the pile when
subjected to lateral loads, bending moments and imposed soil displacements.