Tunnelling work being executed as part of the M6 Stage 1 underground motorway project, which was temporarily paused following the major sinkhole incident in March this year, is expected to resume only next year.

The M6 Stage 1 project, a key element of the NSW Government's transport strategy for NSW, will deliver the missing link from Sydney’s south to the wider Sydney motorway network, and remove more than 2,000 trucks a day from surface roads, helping return local streets to local communities.

The $3.1 billion project, comprising of twin 3-lane, 4-kilometre tunnels, which was scheduled to open to traffic in late 2025, has now been delayed indefinitely as project stakeholders including Transport for NSW, CIMIC Group's CPB Contractors, UGL and Ghella work to resolve the engineering problems and possible redesign of the tunnels, which is expected to further escalate the cost.

Earlier this year, a sinkhole opened up in the vicinity of the M6 tunnelling work at Rockdale, in Sydney's south, causing a large two-level office block to sag in the middle. Fire and Rescue NSW (FRNSW) teams, which rushed to the site, evacuated about 20 people from the area as well as workers from the nearby M6 tunnel, and created an exclusion zone. The sinkhole occurred in an area where the tunnels were only 16 metres below the surface.

Addressing a press conference soon after the incident, NSW Premier Chris Minns spoke about the “major engineering challenges” of the project, and how government engineers were on site to determine the cause and address the issue to prevent recurrence of the problem.

The Rockdale building was subsequently stabilised by pouring 1,800m³ of concrete to fill the sinkhole. However, a few days later, another sinkhole opened up, this time above the tunnel construction site, about 150 metres away from the earlier incident. While the contractors deny any link between the two subsidence incidents, work on a 244-metre segment of the M6 tunnelling project has been paused as detailed geotechnical assessments are conducted to address the sinkhole problem.

According to Transport for NSW deputy secretary Camilla Drover, tunnelling in the affected segment of the M6 project will only resume when complex assessments establish the safety factor and the tunnels are redesigned.

Image: The Rockdale building | Source: Fire and Rescue NSW