Guide to tunnelling
There is nothing simple about the construction of a tunnel. It’s a process of problem solving and discovery considered to be one of the most complex civil engineering challenges to solve.
The stars of the show are two kinds of machine – Roadheaders and Tunnel Boring Machines. Each is suited to different type of work, but both needed to work hard to get through the different solid and hard rock types under our busy city.
At either end of the tunnels are our tunnel portals which are the gateways into and out of the new underground rail network. You can find out more information about them at our dedicated webpage.
Tunnel Boring Machines
Two TBMs headed north from Woolloongabba, breaking through into the station caverns at Albert Street, Roma Street and then finally emerging at the northern portal.
As a TBM moves along it lines each tunnel with strong concrete rings, made of interlocking segments.
These electrically powered tunnelling machines performed the finely-controlled digging needed for station cavern excavation and for the tunnelling from Woolloongabba to Boggo Road.
Tunnel Boring Machines (TBMs) are like underground factories. 165 metres long, they can both tunnel and precisely install concrete reinforcing segments at the same time.
As part of our commitment to sustainability, both of these machines were used on the Sydney Metro project. After they arrived in Queensland, the machines were retrofitted and refurbished in Brisbane in order to prepare them for digging Brisbane’s first underground.
TBMs are traditionally named after women, stemming from a long-standing tradition dating back to the 1500s when miners prayed to their patron saint, Saint Barbara, to protect them underground.
Our TBMs were named after two ground-breaking Queensland women, in honour of their outstanding contributions to the state. The first TBM launched was named ‘Else’ after trailblazing engineer Else Shepherd AM, while the second TBM launched was named ‘Merle’ in honour of pioneering feminist Merle Thornton AM. You can read more about the choice of names for the TBMs here.
Else and Merle commenced tunnelling in February and March 2021 respectively. They were launched from the Woolloongabba station site to dig a tunnel each under the Brisbane River to our Albert Street station. They then continued to the new Roma Street station before both emerged from the project’s northern portal at Normanby in December 2021
TBMs Fast Facts
- The two TBMs used each weigh 1350 tonnes with a crew of up to 15 people working in the TBM at any one time
- The TBMs travelled approximately up to 30 metres per day, operating 24 hours a day, seven days a week
- The front of the TBM is called the ‘cutterhead’ which acts as a drill that can tunnel through rock harder than concrete
- The cutter head measures 7.2 metres in diameter
- The TBMs generated 290,000 cubic metres of spoil as they make way for the twin Cross River Rail tunnels
- Each TBM is fully equipped with kitchen facilities, offices and toilets
Track our TBMs
You can chart the journeys made by our two TBMs – Else and Merle – on our TBM Tracker as they tunnelled from Woolloongabba to Albert Street, before continuing to Roma Street and emerging at the project’s northern portal at Normanby.
The tunnel is lined with strong concrete rings, made up of six locking segments connected by dowels. A TBM installs the segments as it moves along the tunnel. This is followed by the installation of ground support techniques such as inserted rock bolts (metal rods) and concrete which is sprayed on the tunnel lining for strength.
Precast concrete segment fast facts:
- Six concrete segments are used to create one tunnel ring
- 4,157 tunnel rings are required to line both tunnels
- 25,000 segments were produced at Wacol
- The facility produced 140 segments per day
- Each segment is 27 centimetres thick and 1.7 metres long
- More than 105,000 cubic metres of concrete was used to create the segments
These electrically powered tunnelling machines perform the finely-controlled digging needed for shallow tunnel, escape passage and station cavern excavation.
Roadheaders use their rotating excavating head with metal picks to cut rock. An Operator controls the machine from inside the cabin, while a Cable Spotter assists in moving the machine safely.
Roadheader fast facts
- A roadheader is 25 metres long end to end and weighs 115 tonnes.
- They are able to excavate 60 tonnes of rock per hour
- A roadheader’s cone, or ‘pineapple’, will wear away more than 30 picks during an 8 hour shift .
- Roadheaders usually travel 1-5m in 24 hrs
- A total of six roadheaders were used to build Cross River Rails tunnels and stations
Tunnelling FAQsReturn to top
- Offer for a pre-construction property condition survey
- Details of where information is available including online webinars
- Notification delivered to your letterbox in the lead up to tunnelling occuring near your property.
Tunnelling and cross passage construction will occur 24 hours a day, seven days a week.
At the front of the TBM is the ‘cutterhead’, which acts as a drill that can easily tunnel through rock harder than concrete.
7.2 metres in diameter and weighing approximately 120 tonnes, the cutterhead has several cutting discs which roll on the tunnel face and break the rock before it is collected by buckets and passed back to the conveyor.
Travelling up to 40 metres per day, the TBMs progressively line the tunnel with curved concrete segments as they excavate and travel along their 3.6km journey.
When finished, the twin TBM tunnels will comprise of approximately 25,000 individual concrete segments each weighing a hefty 4.2 tonnes.
Roadheaders have bulldozer-style tracks enabling them to move forward as they excavate. They use a rotating pineapple like head fitted with metal picks to break and excavate rock.
Excavated material travels via trucks to the acoustic spoil shed on the surface. This is followed by the installation of ground support such as ‘bolting’, which includes drilling holes and inserting rock bolts before spraying with shotcrete.
Once the rock is excavated, it is placed into articulated dump trucks and hauled to the acoustic spoil shed space at the surface. Here rock is loaded into road trucks and transported to approved disposal sites, or reused as fill in development sites.
Tunnelling is a safe construction technique and is unlikely to cause damage to your property.
Eligible properties near the tunnel alignment have been offered a property condition survey before tunnelling construction. The survey will ensure property owners have a clear record of the property’s condition prior to tunnelling commencing.
We encourage property owners to contact the project team if you have any further questions on this matter.
Residents and businesses along the tunnel alignment may experience some vibration and ground-borne noise during tunnelling.
Ground-borne noise in buildings comes from ground vibrations rather than through the air. Ground-borne noise does not usually disturb building occupants during the day due to higher background noise levels but may be more noticeable at night when surrounding noise levels are lower.
The temporary construction impacts will vary depending on ground conditions, depth of the tunnel, building types and existing background noise levels.
TBM tunnelling will typically take 2-3 weeks to approach, pass underneath and move away from a property, making any impacts short-term to residents and businesses on the surface. Roadheader progress is slower, so residents may feel the impacts for up to two months. If your property is in close proximity to a cross passage you will be contacted by the project team to discuss the expected impacts as this will greatly vary depending on your location.
The project’s community team will work with all residents to ensure they are kept up to date during the entire tunnelling process.
Communication will be sent out ahead of the construction program, so we ask for your patience as we reach everyone.
If your property is located along the tunnel alignment you can expect the following contact from CBGU before we tunnel near your property: