Contractors halt tunnelling on Sydney’s M6 Stage 1 after second incidence of subsidence

Subsidence first occurred during tunnelling works on the project, which involves the construction of twin tunnels of around 4km in length connecting the new M5 motorway at Arncliffe to President Avenue at Kogarah, earlier this month.

On 1 March, a building on an industrial estate in West Botany Street partially collapsed due to subsidence, in an area where the tunnel is 16m from the surface. Work was suspended and an exclusion zone set up around the site. The foundations of the building have been strengthened and the site was declared stable on 4 March.

The second incidence of subsidence occurred on 9 March on what Transport New South Wales (NSW) described as a “contained construction site” that is not accessible to the public and not near any residential or commercial properties.

The site is at the face of the south-bound tunnel, about 12m from the surface on the airport side of West Botany Street.

Australia’s health and safety body Safework NSW has set up an exclusion zone around a 20 sq m area, while geotechnical and engineering assessments take place.

In a statement, Transport for NSW said, “Initial remedial work which will include securing the area has commenced.

“As an extra precaution Joint Venture CGU has halted all further tunnelling work in the impacted area while engineers and geotechnical experts assess further.

“No other sites across the M6 Stage 1 project have been impacted. Any potential changes to construction timelines are unknown at this stage.”

Construction of the M6 Stage 1 started in January 2022 and is scheduled to open to traffic at the end of 2025. M6 Stage 1 tunnel excavation is more than 70 per cent complete.