This highway extension connects the M-5 Motorway to General Holmes Drive, adjacent to the Sydney International Airport in Melbourne, Australia. McMillen Jacobs Associates was specialty tunnel design subconsultant to Hyder Consulting, which served as designer for the design-construct team of Baulderstone Honibrooke/Bilfinger Berger Joint Venture. McMillen Jacobs Associates provided design of twin, 3.8-kilometer (2.4 mi), two-lane highway tunnels, and over 1.4 kilometers (1 mi) of ramps and ventilation tunnels.
The detailed designs of the tunnels included alignment selection, initial and final tunnel support, portal design, groundwater control and drainage, and geotechnical planning and coordination. The design incorporated several unique elements, including underground interchanges, deep portals, vehicle crossovers, disability-compliant pedestrian cross passages, emergency breakdown bays, fan niches, and a complex system of vent-distribution tunnels.
The project team developed several innovative approaches for excavation and support of this largely roadheader-excavated rock tunnel, including the use of the sequential excavation method (SEM). The project’s flat roof with thin shotcrete lining, 20-meter-wide (66 ft) underground intersections, thixotropic-grout sheathed rock bolts and cable bolts, and new shotcrete testing methods all differed significantly from traditional concepts. The owner required a 100-year design life. Design concluded in 2000, and construction, divided into 12 packages totaling AUD$794 million, concluded 6 months ahead of schedule in June 2002.