Ground conditions and building protection for the New MetroRail City Project, Perth

Eric Hudson-Smith and Michael Grinceri

The New MetroRail City Project is due for completion in 2007 in Perth, Western Australia. The project included construction of two underground stations, twin bored rail tunnels of 1.4 km combined length and cut and cover tunnels and dive structures of about 1 km total length. It is the first major underground construction project within the Perth Central Business District. This paper provides an introduction to the project, describes the geology and hydrogeology of the area and summarises geotechnical design parameters for the various geological units encountered. The paper presents parameters adopted for design of temporary and permanent works for the project, the selection of which was governed by the constraints of this project. The values adopted may not be the ‘best estimate’ values of these parameters, but rather reflect a degree of conservatism appropriate to a project such as this. The parameters may not be appropriate for other projects in the Perth CBD. Ground conditions vary significantly along the alignment from soft estuarine muds in an area of reclamation to very dense cemented sands and very stiff to hard clays. Deep foundations for the project extend down into the bedrock below the CBD, a Tertiary siltstone/sandstone. Key geotechnical hazards encountered during the project are discussed. The building protection methodology on the project is described, including damage assessment, condition surveys, monitoring and protection of key structures.