M6: tunnelling resumed in June and the original contract is back on

Tunnelling on the M6 Stage One resumed in June 2026, two years after subsidence events halted work on the twin four-kilometre tunnels between Arncliffe and Kogarah.

The sequence matters:

• May 2021 — CGU, a joint venture of CPB Contractors, Ghella and UGL, is awarded the design-and-construct contract

• February 2022 — construction begins
• March 2024 — two subsidence events; tunnelling ceases in that area
• March 2026 — Transport for NSW issues a notice of default to CGU, requiring it to return to site and resume substantive work including tunnelling on or before 1 May 2026
• June 2026 — agreement reached; construction resumes immediately under the original contract

Under the June agreement, CGU agreed not to pursue contractual claims against Transport or the NSW Government for costs related to the two subsidence events, and will work to rectify that area. The resumption was announced as being at no additional cost to New South Wales taxpayers.

Around 90 per cent of tunnelling is complete and close to half the tunnel fit-out, with roughly 250 metres of main tunnel excavation remaining.

No completion date has been published. Transport for NSW said it would provide an updated timeline "in due course", and that the contractors had agreed to seek to optimise delivery as they remobilised. Anyone planning against an M6 opening date is planning against a number that does not yet exist.

Why this is unusual

Australian megaproject disputes are normally resolved commercially and quietly, with variations and claims settled between the parties and rarely disclosed.

This one ran the other way. A principal issued a formal notice of default against a tier-one joint venture on a $3.1 billion motorway, and the resolution involved the contractor waiving claims and absorbing rectification rather than being compensated.

For contractors, three things are worth taking from it:

Ground risk on urban tunnelling sits with the contractor under a D&C contract, and this is what that means when it goes wrong. Two subsidence events, two years of stoppage, and the cost consequences ultimately landing on the joint venture.

A notice of default is a real instrument, not a negotiating posture. Transport for NSW used one and got work restarted within three months.

The public record here is unusually complete, because the principal chose to announce the terms. That is worth noting in an industry where the commercial outcome of a major dispute is normally invisible.

What is being built

Scope includes:

• Twin four-kilometre tunnels
• Ramps between the main tunnel and the surface intersection at President Avenue
• Tunnel stubs for a future southward extension
• A new intersection at President Avenue, with widening and raising
• Upgrade of the President Avenue / Princes Highway intersection
• Shared cycle and pedestrian paths from Bestic Street, Brighton-Le-Sands to Civic Avenue, Kogarah, including a new bridge over President Avenue
• Tunnel ventilation systems and a motorway control centre
• New service utilities including a permanent power supply line

Who holds it

The unsuccessful shortlisted bidders were an ACCIONA-Samsung C&T joint venture and a Gamuda-BMD joint venture.

The budget figure has quietly disappeared

This is the detail most likely to be missed.

The 2025-26 New South Wales Budget did not declare a total estimated cost for the M6 Stage One, after a $3.1 billion figure appeared in the 2024-25 Budget.

A project cost being published one year and omitted the next, on a project that has been stopped for two years and is subject to a default notice, is not a formatting choice. Whether it reflects an unresolved estimate, a commercial position during the dispute, or something else has not been explained.

It also means the true current cost of the M6 Stage One is not public — and given the two-year stoppage, it is very unlikely to still be $3.1 billion.

The corridor beyond Stage One

Stage One is the first of four study areas along the M6 corridor. The remaining three, and likely future stages, are:

• Section B — President Avenue to Taren Point
• Section C — Taren Point to Loftus
• Section D — Loftus to Waterfall

The tunnel stubs built into Stage One are provision for that southward extension. None of the later sections has been committed.

What to watch

1. Completion of the final 250 metres of main tunnel excavation.
2. An updated completion date. The project was already delayed to 2028 and no revised timeline has been released.
3. Whether a total estimated cost reappears in the next New South Wales Budget.
4. Rectification of the subsidence-affected area, and what method is used.
5. Whether Sections B, C or D are committed — the tunnel stubs exist, the projects do not.

Published 23 September 2026