Liquefaction potential assessment and pile foundation design for high efficiency gas turbines and compressors in Perth

This paper presents a case study of liquefaction potential assessment and pile foundation design for two high efficiency gas turbines and two gas compressors in Kwinana, Perth. Firstly the complexity of the local geology is described with a detailed discussion on the geotechnical risks of the potentially liquefiable loose sands or silty sands of 2 to 3m thickness at varying depths overlying the Tamala Limestone Formation which has potential cavities. The design criteria and the adopted geotechnical parameters for the developed geotechnical model are then discussed. A liquefaction potential assessment approach has been proposed after critical review of the currently published, with an emphasis on the importance of evaluating a suitable earthquake magnitude for a project site. Based on the results of liquefaction potential evaluation and the risk assessment of a number of options, pile foundations have been adopted for the gas turbine generators. A piling strategy has been developed for analysis, design, installation and testing for the proposed Franki piles founded on the Tamala Limestone Formation. The gas compressor raft foundations are to be founded on piles at a shallower depth above the liquefiable loose sandy layer to mitigate the potential risks of loosening/degradation effect of the cemented sands induced by the dynamic loads during the compressor operation. The assessed differential settlement induced by the potentially liquefiable sandy layer has been taken into account by the structural engineer for his detailed design and articulation of the reinforcement.