What is a void and how did it bring Brisbane’s CBD to a standstill? – Michmutters

What is a void and how did it bring Brisbane’s CBD to a standstill?

Towering cranes and scaffolding dominate inner-city Brisbane right now with major infrastructure projects like the Cross River Rail, Brisbane Metro and Queen’s Wharf set to change the face of the CBD.

The developments are also occurring in some of the oldest parts of the city.

Then on Wednesday morning, traffic gridlock and hours-long delays gripped the CBD after contractors working on the city’s new bus network, Brisbane Metro, discovered a “void” below Adelaide Street.

Brisbane City Councillor Ryan Murphy said a decision was made “out of an abundance of caution” to close the stretch between George Street and North Quay, to ensure no vehicles drove over the weak point.

Could this happen again as the city develops?

This is what those in the know say about what could have caused the “void” and the likelihood of it happening again.

What is a void and how common are they?

Put simply, it’s a hole.

Professor David Williams, director of the Geotechnical Engineering Center at the University of Queensland, said in this instance a void “is a loss of support below the ground surface leading to surface settlement”.

“Most people would agree it’s not that common, we don’t usually have the whole of Brisbane brought to a standstill because … a void is revealed,” Professor Williams said.

“It’s more likely a bit of a one-off — it makes sense that it’s related to the construction activity.”

A man with short gray hair and beard smiling outdoors
Professor David Williams says voids are uncommon. (Supplied: Professor David Williams )

A void is also referred to as “ground subsidence”.

It can cause major disruption to roads, resulting in fracture, unevenness, and in some cases, sinkholes.

What happened under Adelaide Street?

The exact cause of yesterday’s void is yet to be determined, but Mr Murphy said it was “uncovered through excavation works”.

“We don’t know how long it was there, we don’t know exactly the cause.

“Workers were doing vacuum excavation … which found a void below one of the traffic lanes on Adelaide Street,” he told ABC Radio Brisbane.

“Some free-flowing material … flowed onto our work site which caused a slight sag in the road.

“Essentially a void [was] created, and that void needed to be filled before we could safely reopen that road – this is not a tunnel collapse.”

Professor Williams said “it’s a little unclear” whether the “excavation activity revealed or caused the void.”

A bus on Adelaide Street in Brisbane
Adelaide Street is subject to heavy traffic and was partially closed as a precaution.(ABC News: Lucas Hill)

What could have caused a void?

Tom Brown from the Rail Tram and Bus Union questioned Brisbane City Council’s explanation.

“The story doesn’t seem to stack up to me, because if there was a void underneath Adelaide Street surely the city’s engineers would’ve picked it up with the ultrasounds when they were marking up this job,” Mr Brown said.


Leave a Reply

Your email address will not be published. Required fields are marked *