The Metropolitan Wastewater Treatment Plant (WWTP) upgrade is one of the most substantial wastewater programmes being carried out in Western Australia, which involved improving the capacity of three major WWTPs in the city. This project involved design of a deep excavation up to 10m to formation level, retained by secant and sheet pile walls tied back with ground anchors. The excavation was undertaken in a mix of highly variable vuggy limestone overlain by the water bearing Perth Sands. The excavation immediately adjacent to the Beenyup ocean outfall pipes and other vital assets and therefore deflection criteria was critical.

Dr Bedi was responsible for extensive FE modelling and detailed design of the ground anchors, secant pile excavation as well as damage assessment of critical ocean outfall structures. The work involved detailed analysis of each individual existing service that is identified and set up the performance criteria to ensure the integrity of them during the construction.