ABSTRACT
M5 East motorway is currently being constructed for the RTA by BHBB joint venture in the southern suburbs of Sydney. The project is being delivered as a Design and Construct Contract. A major component of the motorway is the 4 km long twin 2 lane tunnels. The driven tunnel span ranges from 8 to 19m and rock cover ranges from 4 to 60m. The tunnel is excavated below the water table and driven through sub- horizontally bedded Hawkesbury Sandstone. The tunnel support consists of permanent sheathed and grouted rockbolts or cablebolts and thin shotcrete lining with a 100 year design life. This design reduces time and cost of tunnelling due to the one pass approach to support and lining. It also allows the tunnel to be driven with the minimum possible cross section reducing excavation time. The observational method is ensuring the degree of support placed is optimised by matching the support to the in-tunnel ground conditions.
