The counterfort precast units, utilising an on-site batching plant, were developed by the Baulderstone team from the traditional six metre wide unit with a single central located buttress wall to a nine metre wide unit with a second located buttress wall, providing a more efficient design and minimising the overall unit weight of the wall structure. 
The nine metre wide design also provided additional durability benefits as the majority of the front face of counterfort remained in compression throughout all design load cases. This presence of the compressive stress across the front of the counterfort wall ensured that the concrete would not crack, which meant the rate of chloride ingress is controlled and the amount of reinforcement minimised.
The specification requirement that a 100-year design life in a marine environment be achieved led to special design mixes being developed using a complex chloride diffusion modelling.