Sinkhole puts the brakes on a troubled motorway project

Construction on part of the $3 billion M6 motorway project in southern Sydney has been brought to a sudden halt after a huge sinkhole opened up at the site, forcing workers to evacuate tunnels due to falling debris and leaving a building under threat of collapse.

Workers were left scrambling for safety about 5am on Friday after material began falling from one of the twin tunnel’s roofs, while a two-storey office building sagged into the 10-metre wide hole almost directly above the Rockdale construction site.

Fire and Rescue NSW rushed to the mixed-use building in an industrial estate to find it teetering on the edge of the sinkhole and set up an exclusion zone around the property on West Botany Street.

Firefighters, building engineers and M6 contractors spent much of Friday working on a “make safe” plan to stop further structural damage. Drone footage from Fire and Rescue NSW revealed the extent of the sinkhole, with exposed pipes and building debris lying scattered in the dirt.

No one was working in the part of the industrial complex which partially collapsed into the sinkhole. However, about 10 people were evacuated from another part of the building.

Four workers in the southern tunnel for the M6 below had started to see “a small trickle of material” falling in the construction site early on Friday morning, the Australian Workers Union said.

“They did make efforts to try to arrest that, but as they’re working in natural ground, things are unpredictable,” AWU construction organiser Steve Ackerman said.

“It got progressively worse. So the decision was made correctly, to see staff work to move workers into a safe location away from that.”

He said staff would not return to the site until it was declared safe.

An investigation is under way, but Fire and Rescue NSW and the M6 contractors say it is too early to determine the cause of the hole, the cost of repairs or how long it will take to fix. Contractors began pouring concrete at the site late on Friday to help strengthen the building’s foundations.

The location of the sinkhole near the M6 site in Rockdale.Credit: Google Maps

The under-construction M6 southbound tunnel is about 18 metres below where the sinkhole is.

Ackerman said the collapse was a reminder of the “very dangerous” work involved in tunnelling, citing the long delays to the Snowy 2.0 pumped hydro project after a massive boring machine got stuck in soft rock beneath Kosciuszko National Park.

“There is a certain inherent risk and unpredictability about working underground,” he said.

The cost of the M6 motorway tunnels blew out by about $400 million to more than $3 billion in 2022. The first stage of the toll road, which will link Kogarah to the WestConnex motorway at Arncliffe, is due to be opened to traffic by the end of 2025, about a year later than originally planned.

The cost of the latest cleanup at Rockdale will rest with the M6 contractor, which is a joint venture between CPB Contractors, UGL and Ghella.

Executive project director Terry Sleiman said it was too early to determine the cause of the sinkhole, or the cost to repair the damage.

“There was nothing leading up to [the sinkhole appearing] that would have suggested there were any issues,” he said. “There are a lot of factors, obviously, when we’re tunnelling. There’s water, varying geology and the like, so that’ll all be borne out in the investigation.”

Building engineers and Fire and Rescue NSW have been using laser technology to monitor any further movement in the building as they work to determine the extent of the structural faults.

NSW Fire and Rescue set up an exclusion zone around the building in Rockdale.Credit: Dominic Lorrimer

Fire and Rescue NSW Superintendent Peter Cleary said the 10-metre-wide hole extended under the office building.

“It does go under the building, and it goes under a concrete slab. That’s why we have a large exclusion zone in place around it. We haven’t seen any further expanding of the hole,” he said.

Rockdale resident Janet Lam, whose house is near the M6 tunnels, said she was shocked to hear about the sinkhole. “There is a lot of construction going on, and this was unexpected,” she said.