HDD
Sydney’s forgotten ghost tunnels all powered up with guided boring breakthrough Directhitt Trenchless has completed a project for Laing O’Rourke at Sydney’s Central Station by installing critical electrical infrastructure for the new Sydney Metro.
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s part of the biggest upgrade to Sydney’s busiest railway station in decades, Directhitt Trenchless were contracted to supply and install four DN 630 HDPE liners and PVC electrical conduits to provide 33KV power to the new underground Metro station. The boreholes constructed by Directhitt, connected the 27 m deep metro station box level B2 to an existing ghost tunnel, which was built in the 1920s as part of the Eastern Suburbs Railway line for Bondi and the Illawarra. However, it was never completed. Platforms 26 and 27 have sat unused since and will now house 17 new communications and power rooms to support the new Sydney Metro at Central Station. The 90 m long microtunnells were constructed using an Akkerman Guided Boring Rig, which used a Pilot Tube and Laser Guidance System to accurately drill the pilot hole to line and grade in Class II Hawkesbury Sandstone.
Directhitt chose to use a Guided Boring rig with a compact 3 m jacking frame for the project.
The confined site prevented the use of a typical HDD rig set up, so Directhitt chose to use a Guided Boring rig with a compact 3 m jacking frame. The Akkerman dual-wall pilot tube design allows the pilot tubes to be installed with
pinpoint accuracy while reducing pressures necessary for the long installations. The annular space between the inner and outer tube was used to pump drilling fluid lubricants to the Tri-Hawk drill bit. The inner tube is treated for corrosion
Testing and commissioning of the Akkerman system at the Directhitt yard prior to mobilisation to Sydney.
36 TRENCHLESS AUSTRALASIA APRIL 2022
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