The State Government regional infrastructure project will enable water to be shared among five local council areas – Brisbane, Gold coast, Ipswich, Logan and Scenic Rim councils – moving water from areas of surplus to where it is needed most.
These councils have enjoyed the prosperity of booming populations, a trend that has been accelerating over the last few years. At the same time, they have struggled to manage allocations of an ever-diminishing drought-affected water supply. However, from the start of next year this struggle will ease with the ability of the pipeline owner, the Queensland Bulk Water Transport Authority (trading as LinkWater), to transfer water over an area covering more than 7,500 sq km.
The Southern Regional Water Pipeline Alliance (SRWPA) Program Director Paul Tracey said the project broke new ground with its microtunnelling, tunnel boring and pigging techniques.
“The tunnelling crews have done an outstanding job building ten microtunnels in challenging conditions within very tight time frames, including crossing four rivers and twice crossing the Pacific Highway,” said Mr Tracey.
Ground conditions associated with sinking shafts for river crossings required substantial temporary works to support soft, wet alluvial ground conditions on steep river banks and to create a cut-off against the ingress of river water.
Microtunnelling
The SRWP project completed ten microtunnels in only 18 months. The tunnels have a combined distance of more than 2.2 km and depths of up to 30 m. These tunnels cross four rivers, four roads, a major motorway, including the on and off ramps and the main rail line between Brisbane and the Gold Coast.
As the project was operating on a fast track schedule, tunnelling involved 12 hour shifts that operated 24 hours a day, six days a week, with staff rotating shifts for 12 months.
Some sites were limited in size due to their proximity to suburbs. This meant the crews could not stockpile pipes and had to organise daily deliveries. These smaller sites also determined the positioning of cranes. Instead of having mobile cranes move around the site, the crew secured one crane in an optimal location to operate as needed. They further reduced project risk by implementing physical and mechanical lookouts, as well as proxy volts that sense overhead power lines and automatically shut down the crane whenever the boom comes within a predetermined distance of the hazard.
Tunnel boring
Two Herrenknecht AVN 1500TB microtunnelling machines were put to use 24 hours a day for 14 months, reverting to 12 hour shifts in built up areas.
Both tunnel boring machines (TBMs) operated using a slurry system and were predominately set up for hard rock and mixed ground conditions. The TBM cutters and the slurry system faced high wear risk due to the abrasive nature of the rock. For this reason, a cutter overhaul workshop was set up to rebuild cutters and maximise the potential reuse of parts. A substantial consignment of spare parts for the tunnelling equipment and solids separation equipment was stored onsite to ensure the workshop could immediately respond to maintenance needs.
Mr Tracey said the project saved hundreds of thousands of dollars by recruiting staff to operate the machines, as opposed to hiring subcontractors.
“By doing the more difficult jobs in-house, SRWP built staff capability, ensured the project remained accountable for operating the equipment and better managed potential issues.”
In total, the project conducted 320 vertical metres of jacking and bored 2,382m of tunnel. This included 25 auger bore road and rail crossings of lengths from 30m to 125 m, with a total installed length 1,346 m.
Hyperbaric tunnelling
To manage the hyperbaric conditions involved in microtunnelling, the SRWP project partnered with the Wesley Centre for Hyperbaric Medicine (WCHM) to conduct comprehensive risk assessment.
This assessment helped ensure crew safety by developing procedures, formally certifying machinery and coordinating medical requirements.
The TBMs were certified by the WCHM to ensure the machines complied with work place health and safety regulations and a decompression chamber and hyperbaric medical support were provided on a 24/7 basis during the tunnelling operation.
The SRWPA also co-ordinated all life support systems and support personnel, organised “÷dive’ medical assessments for the caisson workers, lock operators, paramedic and intensive care nursing staff and established and practised an emergency evacuation exercise with SRWP staff.
Pigging
The first challenge for the crew was incorporating the pigging runs into a tight schedule of SRWP works
Mr Tracey said that there are no applicable standards that relate to pigging, only proven operating methods and procedures taken from lessons learnt in the past.
“So you do feel a bit as if you’re working without a benchmark, which can be both daunting and liberating,” said Mr Tracey.
Prior to the works, extensive pigging trials were completed to select the pig type and size used to ensure there was no damage to the bituminous coating to the cement lining inside the mild steel pipe. A pig’s diameter is traditionally designed to be larger than the pipeline. The SRWP crew tailored the pigs to reduce the oversize and avoid “÷snags’ while still being able to pig efficiently. The pigging crew was able to condense the program to gain schedule efficiencies.
Additionally, as a result of the relatively clean pipeline installation, the pig was able to be used without an initial high velocity flush behind the pig, practically halving the time normally taken to do this task. Water flow was controlled by using the pipeline’s temporary valves to manage water pressure in the pipes.
The pigging crew completed their activities as scheduled. The longest pigging run measured 16 km, taking around nine hours and 15.5 megalitres of water to complete.
After pigging, the pipelines will undergo testing and commissioning. All SRWPA projects will have finished commissioning by 31 December 2008.