bus – Michmutters

The viability of a tunnel stretching nearly 12 kilometers from Bald Hills to Kedron and costing at least $9.5 billion is being investigated.

The six-lane tunnel, which would connect with the Airport Link, was part of the outcome of a $10 million federally-funded study undertaken over two years by Brisbane City Council.

It found northern Brisbane’s annual congestion and public transport crowding was costing $312 million per year.

That would rise to $538.5 million by 2031 and $859 million by 2041.

The study found significant community opposition towards any surface road or rail development through the North West Transport Corridor, which had been reserved by the state government since the 1980s.

A map showing the North West Transport corridor stretching from Everton Park north to Carseldine. — The North West Transport Corridor runs from Everton Park to Carseldine and is owned by the Queensland Government.(Supplied: Brisbane City Council)

Stretching from Carseldine to Alderley and including the Chermside Hills Reserve, the land was a “significant biodiversity corridor” likely to contain a number of observed threatened species, the study.

The North West Transport Network study investigated several underground alternatives, including a motorway and heavy rail option, as well as complementary above-ground bus and active transport solutions.

Bus network, another tunnel costed

Brisbane Civic Cabinet Chair for Infrastructure Andrew Wines said all levels of government needed to work together on transport solutions for Brisbane’s north.

“This study demonstrates that doing nothing isn’t an option,” Mr Wines said.

“Brisbane is the fastest growing capital city in the country and our northern neighbors in Moreton Bay are also growing quickly.

The study also assessed building a complementary Bus Rapid Transport system along Gympie Road from the Northern Busway at Kedron to Aspley at a cost of between $758 million and $1.1 billion.

A longer-term option of extending the underground motorway with an 11 kilometer tunnel from McDowall to Toowong by 2041 was also considered.

That tunnel was cost at between $7.8 billion and $11.5 billion.

Brisbane City Council Labor leader Jared Cassidy said Brisbane’s LNP council had announced a multi-billion dollar proposal “without saying when it will be funded”.

“It’s a bit rich for [Brisbane Mayor] Adrian Schrinner to put forward a multi-billion dollar proposal when his administration can’t even complete their own projects,” Mr Cassidy said.

“If this LNP administration can’t finish the North Brisbane Bikeway – how can it propose a multi-billion dollar plan for this North West motorway?

He said it was a proposal for a tolled tunnel.

“This is a backflip from the LNP,” he said.

“It is there in black and white – that the North West motorway will have tolled options considered.

“This plan is meant to be a missing link for the motorway network – but this council is missing the mark.”

Call for government cooperation

Mr Wines said the study had been sent to the federal and state governments, as well as Infrastructure Australia, for consideration.

“Clearly what has been put forward in this study is far beyond the means of local government,” he said.

“We are eager to talk further with the state and federal government about these proposals and hear about any other ideas they might have to deal with northern Brisbane’s transport needs.”

He said the study showed the economic cost of north Brisbane’s congestion would be $1.5 million a day within a decade which was “totally unacceptable”.

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.

“The report I got was they had over-excavated … taken too much dirt out and they obviously weakened the street structure and what council later called a subsidence occurred, which means that Adelaide Street sank.”

Mr Murphy told ABC Radio Brisbane that claim was “categorically untrue”.

“There was no over-excavation,” he said.

While intense rainfall or flooding can create road cavities, Professor Williams said this was a highly unlikely cause.

“It’s not due to surface creeks being revealed, there’s been no flooding associated with this – it’s too high an elevation to be related to flooding in this case.

“It could be related to old buildings or old building foundations, or foundations that were impacted by construction works.”

“People [council] should give as accurate a description of the cause of things like this to allay public anxiety and so on, people are entitled to know what the causes are,” he said.

How big was the void?

Workers have now backfilled the subsidence with quick-dry concrete but the council have not said how big it was.

“I don’t have the exact detail of that,” Mr Murphy said.

“It wasn’t the size of a car or anything like that, the sag in the road was minimal, but obviously this is a street that takes heavy vehicles.

“We weren’t in a position to reopen that [the street] to traffic until the afternoon.”

A void found under the Brisbane CBD is very unlikely to occur again. (ABC News: Lucas Hill)

Could it happen again?

Mr Murphy said the chances of another void being discovered are “very, very low”.

“We are taking steps to ensure this cannot happen again.

“[But] this is one of Brisbane’s oldest streets, it’s built on top of a swamp so the ground conditions under Adelaide Street are very challenging.

“We know that there have been a number of things under there that we weren’t expecting when we went in, things like a road that was built over in the 1970s, the footings of convict buildings – this is a challenging site.”

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