Challenges and lessons learned: upgrading a seawall on compressible clays at the Port of Brisbane

The Future Port Expansion Seawall at the Port of Brisbane was constructed in 2005 directly on the seabed, overlying deposits of highly compressible marine clay up to 27 m thick with undrained shear strengths as low as 5 kPa. The seawall was designed to settle over time and regular upgrades are required, with the first upgrade undertaken in 2013 and the second upgrade completed in 2022. Both upgrades required top-up of the seawall structure crest levels and improvements to the armour rock. A condition and risk assessment were undertaken in 2020 to understand the current and future risk exposure, followed by repair design.

This paper delves into the delivery and construction challenges faced when the Seawall was upgraded in 2022. It outlines the impact of utilising an Early Contractor Involvement phase into the design to validate design feasibility, streamline budgeting, and optimise project timelines. Other construction challenges that are discussed include the criticality in construction sequence due to the requirement for stability berms to be constructed below the tidal zone on soft compressible material, and quality assurance in reusing existing rock armour and core rock. The construction was supplemented by an instrumentation and monitoring regime to observe the deformation and verify the behaviour of the seawall.

The findings of this paper will be beneficial to the development of future seawall projects that are designed to settle over time, and how to mitigate the delivery and construction risks on highly compressible clays in a marine environment.