Application Stories

Perth, Western Australia: The New MetroRail project is an ambitious extension to the existing light rail network that services Perth and its suburbs. It includes construction of 163 kilometers of rail, 20 bridges and structures, and 16 stations.

An important element of the project involves tunneling under the city's central business district to connect the new Southern Suburbs Railway and its stations to the rest of the rail network. Leighton Kumagai, the contractor, is making intensive use of geotechnical instrumentation during the tunneling operations to ensure the safety of workers and the public and to verify design assumptions.

More than 3000 monitoring devices will be placed along the route of the tunnel to monitor for surface and subsurface movements due to excavation and tunneling operations. Pore-water pressures and water levels are also closely monitored. A twelve-member instrumentation team, assembled from Fugro Spatial Solutions and Leighton Kumagai, oversees the instrumentation and interprets the data. The resulting information is quickly transmitted to construction teams to allow modification of their activities, as required. Alarm levels have been established for critical instruments and if alarm levels are exceeded, the construction team is alerted automatically by SMS and email, so that incidents can be investigated and corrective action taken as required.

Surface instrumentation, used to monitor movement of structures, includes automated total stations and electrolevels, as well as manually-read tiltmeters and crackmeters. The surface instrumentation is being used to control compensation grouting, a technique of countering settlements by pumping grout to replace ground losses due to tunneling. Keller Ground Engineering, specialists in compensation grouting, are responsible for this activity.

Subsurface instrumentation, used to monitor lateral movements and settlements, includes inclinometers, rod extensometers, and magnet extensometers. These instruments, with the exception of in-place inclinometers, are read manually. VW piezometers and VW MiniLoggers provide automated readings of pore-water pressures. These are supplemented by standpipe piezometers read with water level indicators.

Thanks to the Public Transport Authority of Western Australia and its Corporate Communications Branch for providing the basis of this story and all of the photographs. For a complete overview of the project, visit the excellent New MetroRail website.

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