In the northwest of the metropolis Perth, along Australia’s west coast, a settlement area for approximately 150,000 inhabitants is being gradually developed. Its center, the satellite town of Alkimos, had to be provided with infrastructure. In Alkimos one of the most efficient urban water systems is planned to be set up. In a first step, a new treatment plant has been built which required an expansion of the main collector network.
To reduce disruptions to traffic and construction works above ground to a minimum, it was decided to drive the tunnels using innovative shield machines. Due to the expected extremely heterogeneous geological conditions, an EPB Shield with dual mode technology was being used since February 2008. This TBM could, if required, be simply converted from EPB to Slurry mode – without major interruptions to the tunnelling process. The micromachine safely and precisely bored its way through unstable aquiferous geological conditions. Using the pipe jacking method, 6,217 meters of tunnel were accurately driven with best daily performance rates of up to 75 meters.