Construction at Kensington
Building the western tunnel entrance involves construction works on Childers Street to build a retaining wall that will support the embankment on the northern side of the rail corridor (east of Kensington Road), which is to be widened to accommodate the new Metro Tunnel tracks.
A decline structure is being built so trains can enter the new Metro Tunnel.
The tunnel entrance structure is proposed to be built via a 'cut and cover' method, which will see them excavated from the top down and the surface then reinstated over the top of the tunnels.
A construction support site on Hobsons Road and a tunnel boring machine (TBM) retrieval box will also be built to support tunnelling works.
It is not proposed that any construction activities for the Metro Tunnel Project will be undertaken in JJ Holland Park, other than potential upgrades to the shared use path.
Construction Look Ahead For 2020
What we are doing
Diaphragm wall (D-Wall) construction
- Construction of two, 280-metre D-walls consisting of over 200 individual panels
- Two large cranes excavating individual panels, up to 20 metres deep and one crane excavating rock and firmer soils at the bottom of the excavation
- Use of the temporary bentonite plant in Hobsons Road to mix, pump and recycle bentonite while D-wall works take place
- For more information about D-Wall construction, see our fact sheet
TBM retrieval shaft construction
- Excavating the TBM retrieval shaft using excavators and trucks to remove material
- Using excavator-mounted jackhammers periodically to break back sections of the tension piles within the shaft as they are exposed. Jackhammers are being used during the day only
- Spraying concrete (shotcrete) to line the walls of the shaft
- Installing steel supports (struts) inside the retrieval shaft to provide the structural frame for further excavation. This involves the use of trucks to transport the struts to site and a crane to lift them into place. Struts are removed as excavation progresses
- Constructing a concrete base slab at the bottom of the excavated shaft.
TBM breakthrough and retrieval
In mid-February, the first Tunnel Boring Machine (TBM), Joan, arrived at the TBM retrieval shaft adjacent to South Kensington station. In mid-March, the second TBM, Meg, will also arrive and break through into the shaft at Childers Street.
When the TBM cutterhead ‘broke through’ into the retrieval shaft, the shaft was filled with water to balance groundwater levels while the final section of the tunnel is constructed. After the water was drained, the TBM cutterhead was retrieved. Water was pumped back to the water treatment plant at the Arden Station site via the TBM.
The TBM cutterhead and front shield sections were cleaned and disassembled using high pressure cleaners and hand tools before being removed from the retrieval shaft and loaded onto trucks using a crane.
The rear (gantry) sections of the TBM will travel back to the Arden Station through the constructed tunnel.
Each TBM is expected to take approximately four weeks to retrieve. Oversized TBM pieces will be transported at night to Arden Station, subject to permits.