- Q How were the tunnels constructed?
- A Three methods were used:
- tunnel boring machines (TBMs),
- roadheader machinery and
- cut and cover techniques.
- Q Why were different tunnelling machines used?
- A Tunnel Boring Machines (TBMs) are used in softer ground, Roadheader Machines are used to excavate hard rock and Cut and Cover is used for excavation work closer to the surface.
- Q How much soil did each roadheader move?
- A Roadheader tunnelling is complete. 17 roadheaders worked on the project. Each roadheader weighed 135 tonnes and moved around 1800 to 2300 cubic metres of soil per week depending on the ground conditions.
- Q How deep are the tunnels?
- A The average tunnel depth is between 25 and 55 metres from the surface to the top of the tunnel.
- Q Where was the first tunnel break-through?
- A
The first breakthrough occurred on 18 June 2010 in the northbound Airport Link tunnel, 22 metres below the surface of Lutwyche Road, near Constitution Road.
The break through point was 629 metres from Truro Street, Windsor and 833 metres from Bowen Hills. The Truro Street roadheader that broke through to the Bowen Hills tunnel, was one of 17 roadheader machines used across the projects.
- Q When did tunnelling begin?
- A Roadheader tunnelling began in March 2009 at Truro Street. 24 hour tunnelling began in May 2009. TBM tunnelling began in July 2010 at Kalinga Park and finished in July 2011 at Lutwyche.
- Q Does tunnelling cause ground movements?
- A Tunnel Boring Machines (TBMs) can cause ground movements (settlement) in the vicinity of the project works. It is impossible to excavate without any associated ground movements, but the magnitudes are controlled through various excavation methods, support types, ground improvement techniques and other design methods.
- Q Are property owners protected from property damage caused by ground movements?
- A
Yes. Before tunnelling, Airport Link’s construction contractor Thiess John Holland was required to carry out condition surveys of properties in the tunnel’s vicinity and implement a monitoring strategy to establish baseline conditions.
Monitoring continues after tunnelling and throughout the operation phase. Under the Project Deed, the construction contractor Thiess John Holland (as delegated by BrisConnections) must repair any damage to property caused by project works.
- Q Is the project monitoring ground movements?
- A
The project implemented a monitoring strategy prior to tunnelling to establish baseline conditions. TJH is also monitoring trigger levels which are set to alert the construction team of predicted settlement throughout the construction phase.
The project must also monitor the actual effects of tunnelling and groundwater drawdown and associated settlement after toll road completion, as part of its Operation and Maintenance activities. This monitoring will continue to occur until the ‘actual effects’ have fully materialised. This will be clear when any ground water drawdown/ settlement has stabilised over a period of time.
- Q Is there any noise from tunnelling activities?
- A
Tunnelling on the projects is now complete. However during tunnelling, regenerated noise was created. This is when sounds from tunnel excavation travel through the ground and cause a building’s flat surfaces to vibrate, creating an audible noise.
The target goal for regenerated noise during tunnelling work is 45 decibels, which is similar to the noise generated from a quiet office.
Acoustic sheds were in place at tunnelling portals (entry/exit points) as required to reduce possible noise impacts.
- Q Are there any vibrations from tunnelling activities?
- A
Tunnelling on the projects was complete in 2011.
Vibrations are commonly experienced during construction, however the levels vary according to construction methods used and the surrounding environment.
The project undertakes regular and ongoing noise and vibration monitoring at various locations across the corridor, with the results published on the project’s website.
- Q Has the condition of structures above the tunnels been reviewed prior to tunnelling activities?
- A It is standard practice to offer building condition surveys to property owners within the immediate vicinity of works to document the condition of properties prior to the start of construction. These condition surveys are provided to the owner free-of-charge and are referred to in the unlikely event that construction causes some impact to buildings.
- Q What happens if my house is damaged due to tunnelling?
- A Measures have been put into place to protect all parties concerned and manage potential damage to property caused by tunnelling. An assessment is undertaken to identify properties near the tunnel that could be at risk of some damage. A pre-condition (building) survey is carried out on properties that may be at risk and a copy of the survey is given to the property owner. This allows for potential construction damage to be assessed and repairs undertaken for any tunnel-related settlement or vibration.
Under the Project Deed, BrisConnections and Thiess John Holland must repair any damage that is found to be caused by project works. The State also has ‘step-in’ powers to repair damage and claim compensation from the project at a later date.
To view CNI’s property damage complaints process click here.
