Codmah is an ISO9001 accredited company that provides civil pipeline, trenching and horizontal directional drilling (HDD) as well as plant and equipment hire services. In May 2005 the company provided initial estimates to Agility for open cut works on the SPL (West) project. Over the following twelve months the Codmah and Alinta alliance progressed through several stages of workshops, figuration of principles, Target Cost Estimates, site office establishment, mobilisation and personnel training. By June 2006 construction was ready to begin.

Area 1, Liverpool LGA (6.8 km)

The pipeline route commenced in Casula at the existing 550NB pipeline, which saw the first crossing of Georges River by HDD into Helles Park and from there the pipeline route followed major arterial, commercial and residential roads through the suburbs of Moorebank, Holsworthy and Hammondville to the second Georges River crossing by HDD in Cantello Reserve.

A trenching crew consisting of a Vermeer 755 Rock Trencher with two side booms and an excavator crew comprising 2 x 20 tonne excavators used in this first area.

The trenching crew was best utilised in the in the street sections where it was able to provide better production rates and therefore reducing time in front of residential and commercial properties and removing all excavated material directly from the trench into trucks for disposal. Codmah is one of the only pipeline companies to use a Vermeer Trencher in built up areas and the crew was required to carry out thorough investigations and preparation works in each section.

The excavator crew was used in both tight grass verge areas and street sections where the Vermeer trencher would not be as efficient. The excavator crew was also more suited to the construction of the pipeline in the grassed section along Heathcote Road where 3 metres of cover was required and the ground conditions were soft with a high water table.

The most difficult challenge to be overcome in this section was the construction of the pipeline through Helles Park. This 500 m section was required to be redesigned due to the presence of garbage cells at 300 mm from the surface and continuing for 3 to 5 m deep. The redesign included the removal and relocation of existing communications, water and electrical utilities; earthworks to remove part of the existing asbestos contaminated batter; and, backfilling and compaction of the pipeline and retaining wall using recycled material from other excavated areas.

Other challenges within this section involved construction along two Roads and Traffic Authority (RTA) roads during night works, construction in unstable water charged ground, five 700 mm diameter cased bores and two 600 mm diameter bed bores, electrical interference hazard from overhead electrical cables, existing underground utilities and two open channel stormwater crossings. Innovative thinking provided practical solutions for the majority of these challenges and some examples are:

* Design and construct Cofferdams at Heathcote and Church Roads for dewatering and sedimentation control while constructing through the stormwater channels. * Design and construct Equipotential earth mats. * Extensive recycling of river sand excavated from Moorebank Avenue and Helles Avenue. * Crib Wall construction technique. * Re-design of pipeline route in particular areas.

Area 2, Bankstown LGA (7.2 km)

After the second HDD crossing of Georges River the pipeline route continued into Bankstown LGA from Deep Water Park to Salt Pan Creek through the Bankstown Tip and along residential and commercial roads in the suburbs of Milperra, Panania, Revesby and Padstow.

This section was constructed using the same two crews in a similar method as Area 1, with the trenching crew utilised in the unsealed areas of Maxwell Avenue and Bankstown tip due to the lengths and accessibility of these sections.

Again, many challenges were presented and conquered including construction through the Bankstown Tip and RTA Easement which involved:

* Site preparation and clearing. * Excavation through the old tip site. * Liaison with RTA and Interlink over access to the easement. * Extensive ground water testing. * Contamination Management Plan – no material removed from this area, all material was kept on site. * Construction of temporary dams for holding 1.8 million litres of ground water. * Environmental issues within the site including contaminated material and the removal of ground water. * Recycle excavated material from street sections for use in the RTA Easement and Bankstown Tip to re-shape and clean up the pipeline easement and construction area. * Restoration of the area.

Other significant challenges included construction in small residential streets with low overhead electrical and communications cables, night works on large commercial roads, community concerns, cased bore across Fairford Road, unstable water charged ground and existing underground utilities.

Some of the innovative ideas which help overcome these challenges were to remove and replace 5 x 1,800 mm Stormwater Pipes on Bransgrove Road to maintain production and continuity of pipeline production, and extensive design of cased bore path at Fairford Road to avoid multiple existing services without the requirement to carry out the bore at extensive depths.

Peripheral Pipeline Installations

Codmah was also responsible for the installation of extensive electrical hazard mitigation devices, cathodic protection ground beds, ALBVs and the tie-ins to the HDD sections at Cantello Reserve, Deepwater Park and Salt Pan Creek. The cathodic protection ground beds were installed in two areas along the pipeline route and involved excavating 300 mm diameter holes that were 43 m deep every 2 m using a vertical auger attachment. The Silicon iron anodes were then placed into the holes and were surrounded by coke. All of the anodes were wired in line and the cables terminated with a CP kiosk.

Two ALBVs were installed after completion of the Hydrostatic testing, one at Helles Park, Moorebank and the other at Bankstown Tip, Panania. The ALBVs were backfilled with stabilised material to provide a firm area to construct the ground beam for the building. The ALBV at Panania was also required to be piled with steel screwed piles in each corner of the ground beam to provide additional support. After installation of the conduits for power, communications and telemetry the ground beam was constructed and cured, the pre-cast ALBV buildings were then brought to site and craned into position.

Hydrostatic Testing and Commissioning

Hydrostatic testing was carried out in August 2007 and was the responsibility of the West and East SPL Alliances. The testing procedure included pre-cleaning, gauging pigs, filling and stabilisation, pressurisation, testing, dewatering and drying. In all, 5.5 million litres of water was removed from Georges River for the test, as potable water was not an option. The test was performed in two sections from firstly Helles Park to Bankstown Tip (8.85 km) and from there the water was transferred to the second section from Bankstown Tip to Mackey Park (20 km). Both sections were tested to a 4 hour strength test at 13,050 kPa and 48 hour and 72 hour leak tests at 11,745 kPa respectively. It was imperative that extensive community liaison was carried out prior to the testing and 24 hour patrols implemented during the strength and leak testing to ensure that no other authorities or organisations were working on the pipe easement for safety reasons. Dewatering of the pipeline was conducted at the Bankstown Tip where there was an existing pond area which could hold the 5.5 million litres of water without any environmental impacts and in turn provided the Bankstown Council with additional water resources for their parks, playing fields and landscaped areas.

Commissioning of the pipeline occurred on 12 and 13 November, with Codmah providing assistance to Alinta.

Conclusion

Overall the project was determined to be extremely successful with the Western Alliance completing the project with an average production rate of 95 per cent of the original estimated rates. Codmah has continued working with Alinta on upgrading the 550 mm diameter pipeline which runs from West Hoxton Receiving Station to Casula and the station at West Hoxton and are awaiting feedback on a recently tendered large diameter gas pipeline project.