Construction of the new M5 highway tunnels is the second element of the WestConnex network in Sydney to complete and open to traffic on 5 July. The AU$4.3 billion route, now known as the M8, comprises twin 9km drill+blast alignments that run from Kingsgrove to a new St Peters Interchange (Fig 1). Meanwhile, progress on the NorthConnex link between the M1 Pacific highway at Wahroonga and the M2 at West Pennant Hills is continuing with opening expected shortly.

M8 will cut travel time between southwest Sydney and the CBD

The M8 will initially feature four lanes of traffic, with capacity to expand to six, and comes into service about a year after the first stage of WestConnex, the new M4 tunnels, opened in July 2019. “We have already seen the huge difference that the new M4 project has made for western Sydney,” said New South Wales Premier Gladys Berejiklian. “We expect similar time savings on the new M8 link.”

The two remaining stages of the 33km WestConnex network under construction are:

• The twin two-lane 7.5km tunnels running between the M4 at Haberfield and the M8 St Peters Interchange, known as the M4-M5 Link and
• The underground Rozelle Interchange linking WestConnex with the City West Link and the proposed Western Harbour Tunnel.

Excavation of the $3.2 billion M4-M5 Link comprises almost 20.8km of mainline drives, on and off ramps, and stub tunnels to the Rozelle Interchange (Fig 3). Construction began in March 2019 by contractor, Lendlease Samsung Bouygues JV, and almost 10km had been excavated as of June 2020, with 28 roadheaders, 15 rock bolters, 14 shotcrete rigs and 47 dump trucks working on the project from four construction sites.

Fig 1. M8 new link from M4 at St Peters Interchange

Fig 2. Two stages of WestConnex complete with two under construction

With the twenty-eighth roadheader beginning operation in May 2020, the project is now reportedly operating the largest number of roadheaders ever used concurrently in Australia. Each roadheader operates continuously, 24 hours a day for seven days a week, and is capable of progressing at an average of 25m per week. At this rate, tunnelling is expected to be completed in 2022 for expected opening to traffic in 2023, when it will provide a western bypass of the Sydney central business district.

The project is also a major contributor to other infrastructure projects in Sydney, generating more than 100,000 tonne of spoil every week. In total more than 7.5 million m³ of spoil is expected to be produced and for reuse on the Sydney Metro, Albion Park rail bypass, and Northern Road upgrades among others.

The alignment of WestConnex runs at up to 58m deep through relatively uniform Hawkesbury Sandstone, briefly passing through Mittagong Formation, Ashfield Shale with residual soils and weathered rock at the portals. Primary support consists mostly of shotcrete and patterned CT rockbolting with heavier support solutions, including canopy tubes/lattice girders, canopy tubes/steel sets, and lattice girders/spilling bars, required in some areas of shallower rock cover. A secondary lining is installed to ensure the 100-year design life. The project is expected to use more than 400,000m³ of concrete, for shotcrete and cast concrete, and 25,000 tonne of reinforcement steel.

Fig 3. Twin 7.5km alignment will link new M4 and M8

Fig 4. Intricacy of Rozelle interchange

The fourth and final element of WestConnex is the complex multi-level underground Rozelle Interchange to connect with City West Link and the proposed Western Harbour Tunnel (Fig 4). Construction began in December 2019 by the John Holland-CPB Contractors JV. The project is being managed directly by Transport for New South Wales, rather than the WestConnex consortium led by Transurban, which is managing development of the other three elements.

To the end of June 2020, more than 3km of various-sized headings had been excavated using 14 Sandvik and Mitsui roadheaders operating and another four being assembled and commissioned. Running at between 35m and 65m deep, the $3.9 billion Rozelle alignment is through unconsolidated sediments and Hawkesbury Sandstone. Ground support comprises a combination of double corrosion protected rockbolts with a layer of shotcrete as required by conditions encountered. Construction of the interchange is expected to be complete for opening to traffic in 2023.

NorthConnex nears completion

Currently nearing the end of construction, NorthConnex features 9km drill+blast twin tunnels to link the M1 Pacific Highway at Wahroonga to the M2 at West Pennant Hills. Commissioning and testing are underway by JV contractor, Bouygues Construction Australia and Lendlease, and it is expected to open to traffic soon.

Surface miner making short work of bench excavating

“Although we have no exact date yet, we are pleased to say we are making great progress and every opportunity is being pursued to open the tunnel as soon as possible,” said NorthConnex in a May construction update.

More than half of the NorthConnex alignment runs at more than 60m below the surface with an 90m underpass of the Sydney Metro Northwest alignment, making it one of deepest road tunnels in Australia. Up to 20 roadheaders completed exacavation with two surface miners excavating the bench. The project also includes 88 cross passages.

NorthConnex is the first in Australia to incorporate a series of internal lighting features that are designed to keep drivers engaged as they drive through the tunnel. These include backlit silhouettes of native birds, trees, and starry skies, placed strategically along the alignment to stimulate driver attention and improve road safety.

As well as WestConnex and NorthConnex, there are a number of other underground highway development projects in the Sydney region including the proposed Western Harbour Tunnel and the Beaches Link, both of which will include underground elements and crossings of Sydney Harbour and the Middle Harbour.

The M4 element of the WestConnex underground highway in Sydney, Australia, has opened to traffic, while work on the other project contracts, including the M5 route, the M5-M4 link, and the Rozelle interchange, continues. The 5.5km M4 route features twin tunnels with a three-lane highway in each direction and was finished on time and within its budget of AU$3.5 billion, ready for its grand opening in July (2019). The M5 link is currently 84% complete and on track to open for traffic in early 2020. Running through the west of Sydney, excavation of the M4 section was completed by the CPB/Samsung/John Holland JV and was undertaken by 21 roadheaders and 11 Robodrill bolting rigs working across four sites. The route also includes 50 cross passages for a total underground excavation of about 14km.

Fig 1. Full scope of the WestConnex project

Excavation work on the AU$4.3 billion WestConnex M5 contract by the CPB/Dragados/Samsung JV was completed in December 2018. The 9km twin three-lane tunnels linking Kingsgrove to a new St Peters Interchange to the southwest of Sydney was also a roadheader operation with 20 roadheaders and 11 Robodrill bolters working from four construction sites. In addition to the main tunnels, the M5 route includes 75 cross passages.

The Lendlease/Samsung/Bouygues JV began excavation on the third element of the underground network, the M4-M5 link, in March 2019. The 7.5km twin four-lane route connects the M4 at Haberfield with the M5 at St Peters (Fig 1). Other elements of the contract include:

• Ramps between the main tunnels and the surface interchange at St Peters
• Ramps between the main tunnels and the surface connection at Wattle Street
• A ventilation facility at St Peters
• Integration with the ventilation facility at Haberfield

Stub tunnels to connect the underground road network to the Rozelle Interchange and to future extensions for the Western Harbour Tunnel and Beaches Link are also part of the contract.

The final contract for the current programme of contracts is the Rozelle interchange, an AU$3.9 billion underground junction that will be one of the largest in the world. The JCL John Holland/CPB Contractors JV, was selected in December 2018 as the successful design and construction contractor. Design plans are continuing and construction is expected to begin this year (2019).

The new Concord Interchange with entrance to M4 tunnels

Both M4 and M5 excavations were supported by specialist tunnel construction software developer, VMT, who supplied the guidance systems for the roadheaders, ensuring they excavated the designed tunnel profile and that bolters correctly positioned the tunnel support. VMT provided full-time service for seven months on the M4 excavation and for a period of about two years on the M5 project. Both were “positive projects,” said Matt Jarvis, VMT Regional Sales Manager.

VMT is now working on the M4-M5 link element of WestConnex with the same teams involved as the initial M4 and M5 projects and a new generation of equipment. The major change to the VMT system is an updated user interface, which is better lit and can be accessed without opening the housing. This eliminates the risk of water and dust ingress, while also allowing for quicker and easier troubleshooting by the project team. VMT have also bid for the final WestConnex contract, covering the Rozelle Interchange. Award of that contract is imminent.

“The M4 tunnels are a game changer for the people of western Sydney, doubling the capacity of the corridor between Homebush and Haberfield,” said Deputy Prime Minister of Australia and Minister for Infrastructure, Transport and Regional Development, Michael McCormack, at the opening. “We know congestion in our cities is a real problem and the Australian Government is doing everything it can to fix it through our record AU$100 billion pipeline of infrastructure projects over the next decade.”