M4 Tunnel’s Traffic Chaos caused by Bulges Found In The Roofing

Sydney motorists were left stranded for hours on Thursday after emergency crews shut down the M4 tunnel due to massive bulges found in the tunnel’s shotcrete roofing.

Transport for NSW Coordinator, General Howard Collins, explained that engineers discovered two bulges in the tunnel roof on Wednesday night, causing an immediate closure while the irregularities were assessed.

The tunnel, part of the WestConnex network and owned by Transurban, was shut down for hours. Some drivers shared that they ended up being stuck for more than four hours before the roads finally reopened Friday morning.

Transurban and Transport for NSW miscommunications

Transurban later said it had notified Transport for NSW early on Thursday morning and issued an alert advising that the tunnel was closed, with traffic being redirected.

“There were delays in Transurban providing clear details about the tunnel issue and their timelines for remediation,” said a spokesperson for Transport for NSW.

“Transurban were also unable to quickly make decisions to stop motorists funnelling into congested parts of the motorway network.”

A westbound lane inside the tunnel was available for use before 2 pm on Thursday, but not underneath the damaged roof section, which was located between Haberfield and North Strathfield, beneath Ashfield in Sydney’s inner west. The two other westbound lanes stayed closed until nearly 6 pm.

What caused the closure? What is shotcrete?

The faulty section was lined with shotcrete, a sprayed concrete mix used to line tunnel walls, subways, and mines. 

Shotcrete is created from a combination of concrete, water, and sand or silt, and is applied to surfaces using pressurised air, with the addition of chemicals that speed up the setting time.

Long-lasting shotcrete can last from 50 to 100 years. However, experts say that unusual geological conditions, such as water leaks or unexpected pressure on the structure, can occasionally cause the sprayed lining to become faulty and create mishaps. 

A geotechnical consultant, Shaloo Puri, told ABC that uncommon events, like a loose rock or water pressure, can put unpredictable stress on the shotcrete. 

“It is important to remove the bulges, because they could fall and that would have been a safety risk,” said Collins to ABC.

“If their prognosis is that it is just the waterproof membrane and the shotcrete, they will remove it and make sure it’s safe and make sure no other materials can have the possibility of falling onto motorists,” said Collins to the Sydney Morning Herald.

“Transurban carried out work overnight to make the M4 tunnel safe and certified for full operation, said a spokesperson for Transport for NSW.

“Transport for NSW wants Transurban to adopt a more proactive approach to managing congestion on their motorways, including improving the generic messaging to motorists who were stuck in the tunnel.”

“Safety is, and continues to be, our number one priority. We thank motorists for their patience during the closure. Customers directly impacted yesterday can contact Linkt on 13 33 31 or via the Linkt app to arrange refunds. Overnight investigations confirmed the small section of roof was made safe,” said Transuburan in a statement.

“Further shot-creting of the roof will be completed at a later date.”