News Articles | 20 August 2018

After leaving the Airport Central Station box in June, tunnel boring machine (TBM) Grace has hit another milestone tunnelling a total of 2.5km from the dive structure in Forrestfield.


To achieve this distance 1462 permanent rings have been installed.

TBM Sandy, whose trailing gantries extend for more than 130m, has now also cleared the Airport Central Station box, however is currently stopped for routine maintenance works a little over 2.2km into tunnel two. While stopped the sacrificial segments used to guide the TBM through the station box will also be removed.

Together the machines have installed more than 16,000 tunnel segments. More than 60 per cent of the segments required to form the tunnel rings have now been produced at a local factory in Forrestfield.

Major changes happening at Forrestfield

The Dundas Road realignment, due to open next week, is the result of months of construction to relocate services, install drainage systems, and build one kilometre of road and two intersections suitable for B-triple trucks (up to 36.5m long).

Once the realignment is open, a section of Dundas Road between Maida Vale Road and Imperial Street will close. This is where Forrestfield Station and the associated feeder roads will be built.

The Dundas Road and Imperial Street intersection will also close. This will allow backfilling of the southern retaining wall to continue and works to begin at the intersection, which will become the station entrance/exit for buses.

At the stowage area, located just south of the future Forrestfield Station, prefabricated steel cages have begun arriving onsite and will soon be used to construct the stowage platform. Excavation of the stowage area's central service trenches and rail track are now also underway.

Infrastructure focus at Airport Central Station 

With both TBMs on their way to Redcliffe Station, construction of station infrastructure at Airport Central is progressing well. Construction of columns between the platform and concourse levels has been able to recommence and further ground slab works are now underway.

Construction of columns and footings to support the elevated walkway, which connects the station with the terminals, are 50 per cent complete. The remainder of the columns are scheduled to be completed this month.

The construction of stair shafts spanning between the elevated walkway and the station concourse level has also commenced this month and includes installation of precast flights of stairs.

Creating a good foundation at Redcliffe Station

With excavation and waterproofing of the station box complete, works are focussing on the construction of the base slab for Redcliffe Station. Nine separate concrete pours of a 1.5m depth will be required, using 5500 cubic metres of concrete, in addition to 1260 tonnes of steel for reinforcement.

The concrete pours are scheduled to finish late-October and the slab will then be prepared for the arrival of the TBMs later this year.

At the Brearley Avenue cross passage site, jet grouting, a technique used to stabilise soils in preparation for tunnelling works, has recently been finalised. A 24-hour pump test has confirmed that no further work is required in preparation of the future connection between the two tunnels.

Rail overpass at Bayswater completed

All four concrete slabs for the rail overpass at Bayswater Junction have been poured and are currently curing. A total of 804 cubic metres of concrete was used to build the structure, which will enable the city-bound Midland Line to cross over the Forrestfield Line.

At the dive structure, excavation is in full swing with excess soil being transported to Forrestfield where it is used to backfill the station's retaining wall.

Meanwhile, after completing open cut pipe works on the main drain relocation, the focus is now on the construction of inlet and outlet structures for the drain. Rehabilitation of Whatley Crescent, where the works were undertaken, is in progress now that tunnelling and backfilling is complete. Due to weather-related delays, reopening of the closed section of Whatley Crescent has been rescheduled for early September.

Upcoming works also include reinstatement of the embankment of the cross passage site at the Guildford Road exit off Tonkin Highway, following the recent completion of jet grouting activities.

Emergency egress shafts taking shape

Work on the project’s three emergency egress shafts (EES) continues to progress this month. The structures, decagonal in shape, are built using the diaphragm wall (d-wall) process. After the d-walls are constructed the egress shaft is excavated and the base slab poured. The final step is to construct the cross passage that links the EES to the tunnels.

Of the three EES, works are most progressed at the Abernethy Road site where excavation of the cross passage is complete, water proofing has been installed and focus has now shifted to installing the permanent concrete between the tunnels and the EES to finalise the cross passage.

At the Airport West EES construction of the base slab for the deepest of the three shafts (34.5m) is due to be completed in the next month before this EES is also connected to the tunnels.

At the third EES site at Wright Crescent, approximately 1200 cubic metres of concrete has been poured for the d-walls and works will now turn to the excavation of 2500 cubic metres of soil from inside the 9m diameter shaft. This EES will reach a depth of 33m before works on the base slab and cross passage commence.

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