Breakthrough! First stage of tunnelling completed
7/2/06
The New MetroRail City Project today achieved an important milestone when a 300 tonne tunnel-boring machine (TBM) broke through into the William Street station.
Planning and Infrastructure Minister Alannah MacTiernan congratulated the Leighton Kumagai Joint Venture (LKJV) on the outstanding engineering achievement.
"Since its launch at the Esplanade station, the TBM has been digging northwards beneath William Street, leaving a circular concrete tunnel in its wake," Ms MacTiernan said.
From next year, trains bound for the southern suburbs and Mandurah will travel along the 470 metre long tunnel which now connects Esplanade and William Street stations.
Leighton Contractors managing director Peter McMorrow said this was a landmark event in the delivery of the city rail project.
"Business in the heart of the CBD has continued uninterrupted, completely oblivious of the tunnelling activity under William Street," he said.
On its way to William Street station, the TBM has passed directly beneath four buildings.
Highly sensitive instruments continuously monitored for any sign of movement in the ground and buildings, which were protected by specialised grouting techniques.
The massive TBM is 6.9 metres in diameter and was purpose-built for Perth's ground conditions by Mitsubishi Heavy Industries in Kobe, Japan.
A rotating cutterhead at the front of the TBM's 10 metre-long cylindrical steel shield slowly bores through the soft sand and clays beneath the city.
Precast concrete segments - manufactured locally by Humes - are erected within the rear of the shield to form the circular rings which make up the tunnel.
The TBM uses hydraulic rams to push off the completed rings and propel the machine forward.
"In the coming weeks, the TBM will be pulled through William Street station," Ms MacTiernan said.
Leighton Kumagai will then launch the machine through the north wall of the station and tunnelling will continue under Wellington Street, the Perth rail yard, and the Horseshoe Bridge.
The tunnel curves to the west and passes under Roe Street before breaking into the completed retrieval structure in the rail yard at Northbridge.
"After breakthrough at Northbridge, the TBM will be dismantled, transported back to Esplanade station and re-assembled for the second of the 770 metre twin bored tunnels," the Minister said.