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Geotechnical work starts on second Sydney Harbour rail crossing

The New South Wales (NSW) government has announced that geotechnical work for the second Sydney Harbour rail crossing will take place over the coming weeks.

Geotechnical drilling will occur up to 70m below Sydney Harbour to help determine the best location for the new Sydney Rapid Transit railway tunnels.

About 30 boreholes will be drilled as part of the Sydney Rapid Transit geotechnical programme, with roughly half of them beneath Sydney Harbour and the rest on land, either side, along the route.

On the harbour, a barge will be towed into position before its four legs are lowered to the seabed as much as 25m below the water surface, then pushed to firm ground on the harbour floor. The barge will be raised up 2m clear of the water surface to provide a platform unaffected by tides, currents or other water movements.

Boring will then begin with a diamond-tipped drill which takes core samples from depths up to 70m below the bottom of the harbour.

To monitor the barge’s interaction with the harbour floor, divers will also be used as an extra visual check, with a preparation dive already completed on Sydney Harbour.

When the drilling work under the harbour is finished, the holes will be filled with cement to create a permanent seal.

It’s anticipated mostly Sydney sandstone and shale will be found along the Sydney Rapid Transit route and the geotechnical work will provide a better understanding of the strength of the underlying rock and groundwater conditions.

The Sydney Rapid Transit line will increase Sydney’s rail network by 60%. The line is scheduled to be in operation by around 2024.

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