Pipe jacks storming ahead in Queensland
In late 2007, TBA completed 10 pipe jacked tunnels on behalf of the Western Pipeline Alliance (McConnell Dowell, Abigroup & GHD) totalling 249 m of 1,800 mm diameter and 120 m of 1,500 mm diameter pipe jacked tunnels. The alliance was constructing a pipeline between Bundamba & Caboonbah in south east Queensland to supply recycled water to Tarong Power Station and Wivenhoe Dam to supplement drinking supplies, which is part of the Queensland Government massive $A10 billion South East Queensland Water grid response to the drought.
Early this year TBA was awarded the contract by the Safelink alliance to install four pipe jacked stormwater tunnels under the Centenary Highway as part of the $A1 billion Ipswich Motorway upgrade project – Wacol to Darra in southeast Queensland. The Safelink Alliance consists of the Department of Main roads, Leighton Contractors, BMD Constructions, Arup & Maunsell AECOM.
In addition to the installation of three 57 m long 2,100 mm diameter and one 65m long 1,800 mm diameter stormwater pipe jacked tunnels, TBA’s scope of work included design assistance and construction of the pit and thrust walls for the 2,100 mm diameter tunnels. These tunnels can be seen in figures 1, 2 and 3.
The construction of the pit and thrust walls was achieved in complicated ground conditions, which required 24 hours of pit dewatering. Each of the tunnels was completed in approximately 10 working days and due to the ground conditions, an intermediate jacking station was utilised on each of the tunnels.
In June this year, TBA also completed 194 m of 1,350 mm diameter stormwater tunnel for Pine Rivers Shire Council, Queensland. The tunnel was completed from one launch pit, jacking 32 m in one direction and then moving the rig 180 degrees, 154 m were jacked with the remaining 8 m being laid in the pit.
TBA is currently working for the Queensland Department of Main Roads in a major project, which involves the culvert replacement beneath the Gateway Arterial and Bracken Ridge Road in Brisbane. Corrosion due to standing water has caused a loss of steel sections in the culvert walls and due to structural failure and danger of sudden collapse, the repair of the culvert was considered a very high priority. The culvert consists of thee helical steel pipes – 1,950 mm, 1,800 mm and 1,650 mm, each 190 m long.
The repair methodology by cutting the existing steel pipes and immediate replacement by reinforced concrete jacking pipes (RCJP) proposed by TBA was accepted by the Department of Main Roads and the slow replacement process began towards the end of last year.
For this particular project, TBA designed and custom built a steel pipe cutting tractor (figures 4 and 5), capable of entering the damaged pipelines and cutting segments not longer than 200 mm. The 1,950 mm and 1,800 mm helical pipes are being replaced with 2,100 mm diameter RCJP and the 1,650 mm helical pipe is being replaced by 1,950 mm diameter RCJP. Throughout the project, additional measures of securing the roads such as horizontal grouting and resurfacing were undertaken by the Department of Main Roads. At present, TBA is working on the third and final pipe replacement with completion expected around September of this year.
Cable installation and culvert replacement in NSW
Towards the end of last year, TBA was awarded the contract to install 120 m of 2,400 mm diameter cable tunnel as part of Energy Australia’s new 132 kV/11 kV Kogarah substation in Sydney. The objective of the project was to design and construct a pipe jacked tunnel beneath the rail corridor and between the Carlton Substation and the new Kogarah Substation, to cater for a total of two 132 kV feeder circuits and up to twenty-six 11 kV feeders.
The overall project was awarded to Abergeldie Constructions, who in turn awarded the pipe jacking part of the contract to TBA. For this project, TBA manufactured the 2.668 m OD diameter rotating head shield and pipe jacking rig in its factory in Oxley, Queensland, as shown in figures 6 and 7.
The pipe jacking installation of the 120 m tunnel took 35 days to complete through Sydney’s sandstone. The receiving pit in this particular project was the basement of the new Kogarah substation (figure 8) and TBA was able to achieve the very strict requirements for both time and final position of the tunnel, which deviated only 10 mm from the original tunnel design.
TBA was also involved in the replacement of another culvert near Somersby for the New South Wales Road Traffic Authority beneath the F3 where the current culvert is substituted with a totally new stormwater pipe jacked tunnel. The tunnel is 86 m long and is constructed using class 6 – 1,500 mm diameter J-series Humes pipes. TBA has undertaken to commence tunnelling from the unconventional higher end of the tunnel at a grade of 6 per cent, which was a result of the site specific conditions. The pipe was completed after only 20 days in mid-July.