Tunnelling has halted on Sydney’s M6 Stage 1 project after a second sinkhole developed.

Workers were about 12m below the surface, excavating the face of the south-bound tunnel, when the hole developed on Saturday, March 9. The workers were evacuated and none was injured.

Safework NSW has been notified, and an exclusion zone has been established around a 20m2 area, while geotechnical and engineering assessments are undertaken.  

Transport for NSW said initial remediation work, including securing the area, had 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,” the organisation said.

The location is within a contained construction area not accessible to the public and the site is not located near any residential or commercial properties. It is around 150m away from another area of the tunnel which was evacuated on March 1 when a large sinkhole appeared and caused a partial building collapse in an industrial estate.

Most tenants affected by the earlier subsidence have been able to access their facilities since Friday. 

Transport for NSW said after Saturday’s incident that no other sites on the M6 Stage 1 project had been impacted and any potential changes to construction timelines were not known at present.  

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

The project includes twin 4km tunnels and tunnel stubs for a future extension of the motorway.