As a result of the Alinta/AGL transaction in 2006, Alinta became responsible for the delivery of the new $100 million 30 km, 500 mm diameter natural gas main and facilities between Liverpool and Marrickville.

SPL Project Manager Peter Sheridan said that despite the many challenges the project team had to deal with in installing a large diameter pipeline through suburban Sydney, the project was successfully delivered in line with the budget and the three year schedule.

The new gas main connects into the existing Sydney Primary Main Network which distributes natural gas to homes and businesses across most of Sydney.

The existing 550 mm primary main was constructed in the late 1970s. It transports gas from the interstate trunk mains in western Sydney and follows a route through major roads and suburbs to finish at Port Botany. Branching from the primary main system is the northern steel primary main which supplies the Sydney north region.

An independent detailed risk assessment was carried out for Alinta on the existing primary main. The risk assessment identified a number of potential hazards that could result in a loss of supply.

The existing primary operation relies on a combination of protective measures, such as a cathodic protection system, anti-corrosion coating and pipeline patrol to ensure its integrity, continuity of gas supply and safety.

Additionally, environmental factors surrounding the primary main have varied since its construction. Rapid urbanisation, increasing easement encroachment, aging of pipe coating and potential external interference all contribute to the threats to the long-term security and integrity of the system.

The risk assessment concluded that “the risk of loss of supply associated with the single primary main is considered unacceptable using the criteria set out in AS 2885.1-1997”. If the primary main was damaged and a section of the main had to be taken out of service, Alinta customers could be subjected to a large scale disruption of their gas supply that could take several months to resolve and depending on the season could affect up to 400,000 customers.

The integration of the new primary main loop (SPL) reduces the risk of both gas supply and safety problems to an acceptable ‘low risk’ level. Also, SPL allows Alinta to overcome the constraints on the existing main for maintenance, repair and inspection. SPL thus provides significantly increased ‘security of supply’ for gas customers in Sydney. In addition SPL also provides capacity for potential increase in gas demand in the southwestern suburbs of Sydney.

Contracting strategy

One of the keys to successful delivery of the project was the selection of contractor partners. Alinta project managed the complete SPL project from concept through to commissioning and was assisted by the following main contractors:

* GHD – detail design and engineering * Codmah – western section, 14 km open cut pipeline construction and installation of two automatic line break valves (ALBVs). * Diona – eastern section, 14 km open cut pipeline construction and installation of two ALBVs. * Coe Drilling – four river crossings using horizontal directional drilling. * Thomas and Coffey – offsite mechanical fabrication and construction of the primary regulatory station (PRS) and trunk receiving station (TRS).

Route selection

The SPL Project passes through the Liverpool, Bankstown, Canterbury and Marrickville local government areas.

The route of the primary gas main was chosen after extensive technical investigations and consultation with key stakeholders.

John Portelli, Construction Manager, who was instrumental in the route selection, said “The principles behind the route selection were to minimise the impact on major public infrastructure, environmentally sensitive areas, residents and businesses along the route; to minimise disruption to the general public and services including power, water, sewerage and telecommunications; and, to ensure safe and efficient construction and operation of the primary gas main.”

An Environmental Assessment identified certain areas of bushland as having particularly high sensitivity along the alignment between Lt Cantello Reserve and Deepwater Park on either side of the Georges River (Hammondville / Milperra).

Both these parks feature bushland listed as endangered ecological communities under both State and Commonwealth Legislation. The construction zone was re-designed and kept narrow to prevent disturbance to the adjacent bushland areas to minimise environmental impacts and the horizontal directional drilling (HDD) was moved to a new location.

Community consultation

Given the potential impact of the development of the SPL on the public, Alinta engaged with local communities on a range of levels. One of Alinta’s primary aims was to minimise impact on major public infrastructure as well as residents and businesses along the route by effective route selection.

Working closely with the four local councils allowed the project team to plan a construction methodology that included streets, parks, reserves and native bushland. Assessments identified that there would be short-term impacts associated with construction including access restrictions, amenity disturbances and traffic diversions. With this in mind, an Environment Management Plan was developed for the project, which provided a framework and procedure to minimise potential environmental impacts such as noise, vibration and dust.

The project community relations team introduced a range of public awareness programs, including public displays at local councils, community meetings, a project specific web site, and directed lines of communication within the company to mitigate the effects of construction on the public.

Pipe penetration testing

The project team conducted a pipe penetration test to measure how well the buried 500 mm pipe can withstand interference and abuse from a third party.

The design of the SPL pipe involves using a calculation in AS2885 to determine if a 30 tonne class excavator was capable of penetrating the pipe and causing a leak. The calculation concluded that the excavator was theoretically capable of penetrating the pipe; therefore, additional protection over many kilometres of pipe would be needed.

The design team felt that the pipe was probably strong enough to deal with a 30 tonne excavator, and the extra protection would be a risk to future maintenance of the pipe.

The only way to prove this and so comply with AS2885 was to initiate a Pipe Penetration Test. A pipeline industry consultant designed and supervised the test (which was approved by Alinta Management) and reported the results. The test required a length of the pipe to be buried and attacked by a 30 (plus) tonne excavator. A number of methods of attack were tried, including one that lifted the front of the excavator off the ground to maximise the force on the pipe.

The rest of the test required an operator to attempt to drill through the wall of the pipe using a heavy-duty jackhammer for one minute, a surprisingly severe trial.

The results proved that the pipe could not be penetrated by the machines considered to be the biggest credible threat and therefore, there was no need for the extra protection.

Richard Mellon, SPL Engineering Manager, said that the results of this test have much wider implications than the SPL project alone. It has provided important data to the Australian pipeline industry in its quest to improve the design tools of the pipeline code AS2885, by getting a better balance between a pipeline that is safe and a pipeline that is over-designed and hence unnecessarily expensive to build and, sometimes, more risky to maintain.

Environmental

Work done in the planning phase of the project allowed the identification of many items of environmental and heritage conservation significance. However, given the challenges of finding a suitable route through the urban environment for a gas main of this length it is impossible to avoid all sensitive environments and heritage items.

Where sensitive features were encountered along the alignment the potential impacts to these features needed to be minimised through minor alignment changes and the adoption of less disruptive construction methods and techniques.

The sensitive environments and other features encountered along the route were varied and included major watercourses with extensive riparian zones, areas of high water table, threatened bushland communities, threatened flora and fauna species and items/areas of European and Aboriginal heritage significance. Specific attention was paid to each location in order to determine the alignment and method of construction that represented that least potential impact overall.

Working around existing services

This project presented unusual challenges when compared to the usual large diameter transmission pipeline construction which takes place in often remote locations across Australia.

A typical pipeline will cross another service every 10 km. In the case of the SPL project the main crosses paths with hundreds of major and minor services every kilometre and so extensive fabrication and pipe bending was required. All excavation areas on this project are considered as confined spaces due to the depth. Benching of excavations is often not practical so most bell holes required shoring boxes or sheet piling to be installed. Close attention to services searching and extensive pre planning of activities was essential to maintain acceptable production rates.

While a good day on a cross country pipeline is 3 to 7 km, a good day on the SPL was 200 metres between four work fronts.

The majority of the construction of the SPL gas main was typical open trenching methods that involve excavating a trench, laying a section of the pipe and backfilling the trench with suitable material. Due to the nature of the areas under construction, a considerable challenge was the disposal of the quantity of spoil that would normally be considered clean fill.

There were also four HDD water crossings and twelve significant cased bores under sensitive areas and major road crossings.

Safety

The safety of SPL employees, contractors and the community was an essential part of the project. SPL adopted the goal of “Zero Harm – Safety First”.

The key to achieving this goal on the SPL project was thorough identification of project hazards and the selection of control measures to manage the risks to an acceptable level. The importance of Safety as a ‘non negotiable’ was continually demonstrated by all staff on the project such that the project achieved an enviable safety record for the work undertaken.

The SPL Project worked, with Australian Standards and Dial-Before-You-Dig, to provide councils and constructors a high level of safety post-construction. To reduce the number of digs on the pipeline that may lead to damage, the project provided extensive as-built mains laying information for DBYD and developed and installed a new underground warning tape system to provide future operators with better early warning that they are near an underground gas main.

Ground conditions

95 per cent of the Sydney Primary Loop Project construction was open cut (trenching) and the construction crews encountered the full range of underground conditions from heavy rock, running sand, contaminated soils and high water tables.

Innovative use of equipment was devised by the construction partners to counter these conditions. Specialist equipment was required to construct through the rock areas including rock saws, rock breakers, vibration monitoring equipment, noise monitoring devices and water spray to manage dust. A Vermeer trencher was used in suitable areas and good production was achieved.

Helles Park – Moorebank

Helles Park is located at the western end of the SPL. Within the park there is some 1,000 m of pipeline, which includes 700 m of open cut embankment, 300 m of HDD, a PRS and an ALBV. Originally, the Helles Park alignment was to be constructed using open cut trenching as it the most cost effective solution in terms of construction, environmental, risks, hazards and safety costs.

When planning the SPL alignment in April 2005 the park was considered to be one of the better sections however, just before construction was to commence in May 2006, Liverpool Council advised that there was an “unhealthy building land notice proclaimed for parts of Helles Park”. Soil testing results confirmed that the Helles Park alignment was formerly a landfill site and thus unsuitable.

This posed risks to not only pipeline integrity but to the environment, personnel and local community as contaminates would be exposed via open trench construction methods and site preparation works for the pipeline facilities (PRS and ALBV).

The project team considered the few available options and engineered a solution for the pipeline to be placed in the existing embankment that runs along the eastern boundary of the park. The embankment did not have a high concentration of garbage and the natural ground was at the most 4 m in depth. Boreholes were drilled along the embankment to determine the depth of the natural conditions and soil samples were taken every 500 mm of the borehole.

The pipe could be laid at the toe of the embankment with a crib wall for protection and to allow the appropriate cover. The crib wall was designed as it has the flexibility to move with the settlement of the ground unlike other retaining wall options.

Although the garbage cell was deposited between 25 and 30 years ago, there may still be minor ground movement due to the decomposition of the garbage. Settlement monitoring will be conducted using survey of pipe location to detect any movement of the pipe.

Both the PRS and ALBV also had to be relocated because of the contamination. This involved significant redesign to fit them into available non-contaminated area on the edge of the park.

A year after finding Helles Park unsuitable, the facilities have been completed, the pipe has been installed behind the crib wall to AS2885 all with full council approval.

Commissioning and handover

To ensure a smooth handover of the asset, often the bane of many projects, from the project delivery team to the operating groups, Alinta established a ‘completions team’. This team led by SPL project members incorporated representatives from Asset Services and Asset Operations.

The team was charged with ensuring that in addition to complying with the construction aspects of AS2885, the Alinta Asset Management and Operations requirements were to be completed and implemented in time to suit the project schedule. These requirements included such areas as revised control and operating procedures, SAOPs, ERPs, training of operations & maintenance personnel and the provision of the required manuals and records.

The result was a success and the ‘completions team’ model will be used as appropriate in future Alinta projects.

Summary

Given the enormity of the task and the plethora of obstacles, the on-schedule and on budget completion and handover of the SPL was no small feat. This can be attributed to the detailed planning and implementation that incorporated consideration of the project requirements of safety, technical, engineering, environmental, construction, community and stakeholders.

“The success of the project is due to all those personnel involved who contributed their best for the project,” said Mr Sheridan.