Design, Lane Cove Tunnel, Sydney, Australia
The Lane Cove Tunnel (LCT) is a twin 3.6 km tunnel and 3.5 km of bridge and road upgrades to link the M2 Motorway with the Gore Hill Freeway. Thiess and John Holland were awarded the $1.1 billion contract by Connector Motorways to design and construct the tunnel.
PSM was engaged as a sub-consultant to the design team, responsible for the eastern end of the LCT which went beneath the backfilled Artarmon brick and the design of temporary surface works design.
PSM were also engaged as specialist consultants to the design team for the recovery works following the collapse on 2 November 2005.
engineering and technical opportunities
The twin 10 m span tunnels beneath the backfilled Artarmon brick presented one of the highest construction risks to the project. Communication between the designer, PSM and the tunnelling crews was paramount.
Design and construction was governed by the:
- Existence of a high water table, the impacts on groundwater and hence settlement
- Minimum 2.5 m rock cover separating the tunnel from 18 m of saturated backfill and the operating Gore Hill Freeway
- Narrow rock pillar between the twin tunnels which reduces in width from 9 to 1.5 m at the portal.
approach and innovation
Following a rigorous assessment, PSM’s tailored approach included provision of probing, pressure-testing, cement grouting, spiling, erection of steel sets and shotcreting, a unique approach in headings largely comprised of good quality sandstone. This method was used due to the low rock cover separating the saturated backfill from the tunnels.
PSM provided the technical and practical knowledge for the design of the twin 10 m span tunnels beneath the backfilled Artarmon brick pit ensuring this high-risk area was constructed systematically and safely. The Lane Cove Tunnel opened to traffic on 25 March 2007, seven weeks ahead of the contract delivery date.