NorthConnex nears public opening 03 Sep 2020

The NorthConnex underground highway in Sydney has had its opening delayed, according to toll road operator and project owner Transurban. According to Transurban CEO Scott Charlton, opening will be later than had been anticipated as the commissioning has been complicated by Covid-19, “which has caused issues around supply and overseas workers, as well as to the working environment”.

Drive through of the completed highway link

Construction by 50:50 design-build JV of Lendlease and Bouygues began in 2015, with opening originally expected in 2019. This was pushed back initially following excavation delays blamed on geotechnical and logistical challenges by the contractor.

The AUD$3 billion route will be the second major underground highway to open in Sydney in 2020, following the new WestConnex M8 in July. It will link the M2 Hills highway around the north of the city with the M1 Pacific route north to the Central Coast, Newcastle and Hunter regions of New South Wales, adding capacity to the surface Pennant Hill Road that it is designed to upgrade (Fig 1).

Fig 1. NorthConnex links the M1 and M2 highways and bypasses 21 sets of traffic lights on the congested Pennant Hill Road

In addition to the 9km mainline tunnels, the project includes underground ramped interchanges at north and south portals and 88 cross passages. In total 21km of tunnels were excavated through Hawkesbury sandstone and Ashfield shale between May 2016 and the end of 2018 by 20 roadheaders supplied by Sandvik and Mitsui, as well as two Vermeer surface miners. At an average 60m deep, and at 90m at the deepest point, NorthConnex is reportedly the deepest road tunnel in Australia.

Primary support through the Hawkesbury sandstone is provided by rockbolts and steel/synthetic fibre-reinforced shotcrete. This was followed by a spray-on waterproof membrane with final lining of synthetic-fibre reinforced shotcrete. Through the poorer-quality Ashfield shale, canopy tubes and steel sets were used as primary support, with a waterproof sheet membrane, and final reinforced cast in-situ concrete lining. 250mm-thick continuous reinforced concrete also forms the road deck, which is designed to withstand up to 5,000 trucks that are expected to use NorthConnex every day.

More than 2.3 million m³ of excavated material was removed by vertical conveyors at each of four production shafts, eliminating the need for access adits and helping to reduce the surface footprint of the project. Conveyors were also used to transport 1 million m³ of the spoil, at a rate of 2000 tonne/hr, into the nearby Hornsby Quarry, where it was used for restoration work. Sustainability was a key element of the NorthConnex project, winning it several awards for sustainability and environmental considerations.

According to Transport for New South Wales, the new highway will allow motorists to drive between Melbourne and Newcastle, a distance of more than 1,000km, without passing a set of traffic lights, as well as easing congestion on Pennant Hill Road, one of the most congested in Australia. Initially opening with two lanes in each direction, and with capacity to carry more than 100,000 vehicles per day, the tunnels allow for future expansion to three lanes, as needed.