From the magazine, Microtunnelling, Pipe jacking, Tunnelling

Breaking new ground in QLD

Tunnelcorp is a multi-disciplinary Trenchless Technology contractor operating throughout Australia and New Zealand, providing slurry and vacuum microtunnelling, pipe jacking, box culvert jacking, auger boring and canopy support pipe structure services.

Tunnelcorp’s current projects include two 1,500 mm inside-diameter microtunnels under two freeways in Brisbane for the Logan Water Alliance, 988 m of 1,400 mm gravity sewer,
18 manholes for Queensland Urban Utilities (QUU) at Ipswich as well as a canopy support structure, and a 52 m long 7.8×4.6 m jacked-box culvert under a rail line in Gladstone for the Wiggins Island Coal Export Terminal.

Box jacking in Gladstone

In Gladstone, 1,144 m of roof and floor canopy support bores have been completed and the box culvert jacking will commence mid-June 2013. Tunnelcorp has constructed a 6,000 tonne
jacking system incorporating
8×750 tonne rams with 1 m stroke powered by four electro/hydraulic power packs. Each 1.5 m long culvert segment weighs 60 tonnes with a completed jacked culvert weight of 2,080 tonnes.

Microtunnelling in Brisbane

Logan Water Alliance awarded a contract to Tunnelcorp to complete bores under two major freeways south of Brisbane. The scope includes the constructing launch and receival shafts, installing 1,500 mm inside diameter concrete jacking pipes 174 m and 180 m
long, installing 1,200 mm mild steel cement lined carrier pipe inside the encasing pipe, and grouting the annulus and backfilling the shafts.

Tunnelcorp chose to construct the launch shafts utilising segmental lined underslung Humes caisson sections due the shafts being located in a flood plain. During shaft construction, the area was flooded twice with water extending 1 m above ground level and the sealed shafts performed well. The receival shafts are constructed with sheet piles, with whalers located in an area less prone to flooding.

As at May 2013, the two launch shafts have been constructed and the bore under the M1 Freeway is in 90 m. Tunnelcorp’s particle size distribution recycling system is being used to recycle the slurry. The high plasticity clay with occasional sand lenses has created premature thickening of the slurry water, requiring the disposal of 30,000 litres
of slurry daily. In conjunction with Tunnelcorp’s mud suppliers, AMC Tunnelcorp has added additional additives to break-up the clay and floc the slurry tanks in an attempt to reduce slurry disposal costs and increase production. At the 90 m mark, a high speed centrifuge was also installed to reduce slurry disposal costs.

Tunnelcorp’s computer aided Herrenknecht AVN1500TB slurry microtunneller has consistently progressed in high plasticity clay at 20 mm per minute and the maximum deviation from line and grade has been 6 mm to-date. This is a reasonable production rate given a mixed ground head has been employed due to the possibility of striking rock under the M1 Freeway. Tunnelcorp expects to complete the project in September 2013 and is looking forward to its next challenge.

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