‘Extremely delicate’ Brisbane tunnel project promises to free up the CBD

Brisbane’s newest tunnel will finally link the Inner Northern Busway, which runs past the Royal Brisbane and Women’s Hospital, with the South East Busway that extends to Eight Mile Plains.

Underneath the CBD, workers are forging ahead with the first tunnel to be dug in “soft rock” in Australia, using engineering techniques fine-tuned beneath the waterfront Sydney Opera House.

The Brisbane Metro tunnel will travel just 213 metres under Adelaide Street, between George Street and King George Square, but play a critical part in the transport network.

It will take buses from Adelaide Street and channel them underground to the King George Square station. Buses provide two-thirds of public transport journeys in Brisbane.

The goal is to reduce by one-third the 385 buses which now run on CBD streets and ease the underground bottleneck emerging in the adjacent Queen Street station.

On Tuesday, the media was allowed into the worksite, which will see a tunnel forged through soft soil and around gas, telephone and data services as well as numerous buildings - some historic.

Brisbane Metro’s Adelaide Street tunnel project manager Jose Antonia Sanchez.Credit: Tony Moore

“Since 1988, our city’s buses have used the Queen Street bus tunnel and Adelaide Street to connect through the CBD,” Brisbane City Council transport committee chairman Ryan Murphy said.

“But that is causing massive bus congestion in the CBD.

“That means long trips for commuters, waits sitting on Victoria Bridge and on the road network.”

The council expects the tunnel to improve on-time running by 50 per cent.

Brisbane City Council’s transport committee chair Ryan Murphy is briefed on progress by senior engineers Jose Antonia Sanchez, Brian Marshall and Stephen Hammer.Credit: Tony Moore

Murphy said the tunnel needed to be excavated slowly because it was shallow, the rock known as Brisbane Tuff was highly weathered and relatively soft, and the route must avoid building foundations.

“In Brisbane the vast majority of tunnels are dug through hard rock - projects like Clem 7 and Legacy Way - so this is an extremely delicate project and at any one time we are only metres away from car parks, and the foundations of other buildings,” he said.

Project manager Jose Antonia Sanchez said it was “quite a challenging tunnel,” having to be built beneath temporary 16-metre steel canopy support tube beams.

“It is very shallow, only a few metres under the street, and it is probably the first tunnel in Australia done in soft ground,” Sanchez said.

Sanchez said the cautious approach meant slow progress - the team was tunnelling “one metre at a time” to ensure there was no slippage.

“We have used this technology under the Opera House in Sydney. It was in different conditions, but it was the same challenges.”

The work will take about 18 months, with seismic movement monitored daily before tunnelling commences.

Subsidence in August 2022 required the closure of part of Adelaide Street at peak hour, causing two-hour traffic delays.

Excavations have unearthed old bricks and bottles from Brisbane’s convict-era days and a convict-era wall from one of Brisbane’s original hospitals.

The project has also increased in cost, from $980 million to $1.4 billion and now $1.7 billion, which includes a new station at the Gabba.