A soil-nailed excavation for the Brisbane Airport Link project, Australia

The Airport Link project in Brisbane, Australia, involved 15 km of tunnelling including 5·7 km of twin road tunnels, busway tunnels and connecting ramps. The Kedron area is the location of a number of entry and exit ramps which join the tunnel. The construction site consisted of a number of tunnels crossing each other and formed using a number of techniques. Access was required to a maximum of 18 m below ground level to allow for the construction of a pile-supported capping slab, which would act as a roof slab for a mined tunnel passing east to west. This paper presents details of the design and construction of the soil-nailed walls which provided support to three sides of this excavation. The excavation also provided access for commencement of a mined tunnel using canopy tubes heading eastward through one of the soil-nailed walls. The project constraints meant that the solution required close coordination between the contractor and the designers of the temporary and permanent works. The excavation was constructed successfully and has now been decommissioned. Design risks were managed throughout construction through continuous on-site observation and a comprehensive monitoring programme.