The key purpose of the construction alliance was to design and deliver a pumped raw water pipeline from Wivenhoe Dam to Cressbrook Dam.
The $187 million pipeline project runs approximately 38 km through rural properties and state forest within the Somerset Regional Council boundaries. The pipeline is designed to pump in one direction, east to west, to where it is needed.
The necessity of a quick delivery date was reflected in Toowoomba Regional Council (TRC) modelling, which found that the three dams supplying water to Toowoomba would run dry by the second half of 2010 without significant inflows.
The combined storage level of available drinking water in TRC’s three dams had dropped to 7.9 per cent in late 2009, adding further urgency to the project, despite the strict Level 5 water restrictions in place. In delivering the Toowoomba Pipeline, the grim situation facing Toowoomba’s 125,000 residents on town supply has been alleviated with at least 16 per cent combined storage in the dams at present.
The 39 ML/d capacity pipeline transfers raw water at an elevation difference of approximately 250 m based on water levels and dam wall heights. The pipeline can be readily upgraded in the future to transfer up to 49 ML/d.
Mild steel cement lined (MSCL) pipe was supplied in lengths ranging from 6 to 13.5 m. The wall thickness of the pipe varied between 5 mm and 6 mm for the PN21 and PN35 pressure classifications. The pipe was supplied with external Sintakote protection and internal protective bitumen-based coating was applied over the cement lining.
Jointing along the project was completed using a number of techniques, including rubber ring joints (RRJ) and conventional welded spigot and socket slip joint (SSJ), and split weld coupling configurations.
Tees for scours and air valves, as well as lobsterback style bends and main pipeline specials were all supplied with heavier steel wall to facilitate minor onsite configuration adjustment. Welded SSJ jointing was used upstream and downstream of bends to negate the need for heavy buried concrete thrust blocks.
Although ground conditions were generally good – ranging from red volcanic and sandy soils to clays and weathered rock – approximately 6 km of 14 km of the route right-of-way (RoW) was obstructed by hard bedrock which could not be trenched by WDS’s T1055 Vermeer Trencher or excavated by conventional means.
Crushing and screening of the line blasted rock (blue metal) was undertaken using a mobile rock crushing and screening plant established for this project in the previously inaccessible Cressbrook Creek gorge.
Welding procedure qualification used a mix of manual metal arc welding and flux cored arc welding practices, with full integrity testing of each welded joint by magnetic particle/non-destructive testing methods and holiday testing to ensure coating integrity.
Once each joint and its coating integrity were verified, the location and elevation of each of the 3,600 pipe joints was surveyed for as-constructed record purposes and recorded in a GIS geo-database along with the barcode identifier of the two pipe elements adjacent to each joint. In this way, the manufacturing and construction quality records are fully integrated with the as-constructed position of the pipe in the ground.
Peak pipe-laying activity from March until September 2009 was carried out by multiple specialised crews with a high degree of focus on safety, often in challenging construction locations.
By September 2009, even though the length of each of the hydrotest sections ranged from 2 to 6 km, all pressure tests had achieved a 100 per cent first-time pass without any problems – setting an industry benchmark.
Subsequent to hydrotesting, the pipeline was swabbed in reverse direction and, following commissioning, fully pigged using the pumping installation for verification and training purposes.
Conservation and effective reuse of topsoil on every property was rigidly adhered to. Subsequent final restoration and local adjustment to seeding mixes in consultation with local pastoralists has resulted in ground cover to almost as good as original within several short months.
Extensive local draining and contouring works were required within the right-of-way, as well as occasional adjacent pastoral allotments to ensure appropriately functional drainage would not compromise future pipeline maintenance access or present hazards to livestock or other uses.
The project teams overcame several significant challenges while achieving all project milestones despite significant wet weather encountered in late 2008/early 2009.
Challenges included traversing rolling hills and extreme gradients such as crossing the Munro’s Hill area. Constructed pipeline gradients exceeded 40 per cent for several hundred metres, which required extreme care in planning all vehicle operation and movement of materials.
Safety in design, construction methodology, materials, equipment, plant selection and operation were at the forefront of the project at all times.
WDS Construction CEO Robin Bailey said “The safety performance has been nothing less than outstanding. We’ve completed around 600,000 man hours with a total recordable injury frequency rate of 3.6. This is well below the industry standards.”
Direct economic benefit of the project included an estimated expenditure of almost $12 million in the local community, and resulted in direct employment for 77 local staff, out of a peak of 298 workers.
* March 2008 – alliance of LinkWater Projects, WDS Ltd, Clough, and AECOM appointed and design commenced. * September-October 2008 – established camp and services, compounds, laydown areas, RoW access. * October 2008 – commenced haul road construction. * March 2009 – commenced pipe laying. * September 2009 – completed pipe laying. * December 2009 – commenced pump station and pipeline commissioning. * 18-19 December 2009 – early water stretch-target achieved as programmed (24 hours pumping continuously into Cressbrook Dam). * 15 January 2010 – functional testing completed, commence 14-day continuous reliability trial. * 29 January 2010 – completed reliability trial target (pipeline commissioning effectively complete). * 5 March 2010 – pipeline handed over to client.