From the magazine, HDD, Microtunnelling, Pipe jacking, Tunnelling

QLD’s unseen scene

Tunnelcorp has just completed two 1,500 mm inside diameter microtunnels under two freeways in Brisbane for the Logan Water Alliance.

Each drive was 180 m in length through unfavourable high plasticity clays. Production rates varied between 6-17 m per day with slurry returns at a greater frequency than envisaged due to the ground conditions.

Tunnelcorp used its Herrenknecht AVN1500TB for the crossings in conjunction with its PSD recycling system. The recycling system was utilised to recycle and re-use the drilling fluids until the solid content dictated a change out of the storage and active tanks, often on a daily basis.

The finished bores were completed to a high degree of accuracy, with both bores exiting within 10 mm of designed line and grade. Tunnelcorp’s scope was to construct the launch and receival shafts, install a 1,200 mm MSCL pressure sewer main, hydrotest and backfill.

Box jacking in Gladstone

In Gladstone, Queensland, Tunnelcorp are well under way with a large box culvert jacking operation for the WICET coal conveyor system. The 1.5 m long jacked culverts each weigh 60 tonnes and each culvert is advanced using a new custom built 6,000 tonne jacking system. Roof and floor canopy support bores 1,144 m in length were installed to support the rail line above and provide a bond breaker system to ensure the material above is not disturbed.

The culverts pass only 4 m below the Main Northern Rail Line. This line carries up to $A20 million of coal per day. The client gave instructions “Please don’t damage the rail.”

The ground conditions were problematic with the top 3.5 m of material consisting of cobbles and boulders of Chert and Basalt in a clay matrix and the lower 1.2 m of solid rock requiring rock breakers.

Day and night operations were undertaken and production averaged 2-2.5 shifts per segment in difficult ground conditions. Accuracy was monitored with lasers and traditional survey equipment and the 32 tonne steel cutting had 80 tonnes of steering rams attached to provide all directional steering.

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