With construction beginning in mid-2006, the SPL is a new 30 km natural gas main that will connect into Sydney’s Primary Main Network. Connecting Liverpool and Marrickville, the pipeline is being built in a bid to improve security of supply and increase the capacity for long-term growth in both the eastern and the southwestern regions of Sydney.

An 11 km section of SPL main was previously constructed in the late 1980s and early 1990s. The SPL section now under construction will tie into this existing primary main at Liverpool. The new SPL route will complete the looped feed for the Southern Primary Main system which is the major feeder gas main for Sydney.

The 500 mm diameter pipe is being constructed from X42 steel, with a wall thickness of 12.7 mm. The main will be laid at a minimum depth of 1.2 metres in most areas, although conditions in some areas necessitate laying the main in shallower depths. Additionally, near some utility crossings it is estimated the main will be 6 metres in depth. Significant portions of the main have already been laid at 4 metres depth due to the presence of extensive existing utilities.

Construction has been completed on almost 16 km of the pipeline. However, the route development process was particularly demanding - both due to factors related to the negotiation of extensive existing infrastructure and also the uniqueness of the natural environment.

“Finding a route through a major city was challenging. Beside the normal engineering considerations for a pipeline, factors such as negotiating the numerous existing services, stray electrical currents from electrified railways and both overhead and underground power cables had to be considered,” said Peter Sheridan, Senior Project Manager.

Zone Manager John Portelli also noted that the effects on traffic flows and the public was a major consideration and had to be carefully negotiated. Space for construction of above-ground facilities such as regulating stations and line break valves was difficult to work into a usable route as these structures needed to be located to make use of the existing large secondary distribution mains along the route.

The redundancy of infrastructure also proved to be challenging. Some of the older parts of Sydney which have significant underground infrastructure were not always mapped. Similarly, local councils were not always aware of latent conditions such as old disused garbage tips that have been capped and forgotten.

The urban environment also provided its fair share of obstacles, from high water tables and water charged ground, as well as the requirement to remove rock in highly congested areas.

Conversely, the route also encountered extensive early European and Aboriginal heritage landmarks, with many structures of historical and cultural significance being located along the route. These included Deepwater Park in Panania and Lieutenant Cantello Reserve in Hammondville.

These areas featured endangered bushland communities, threatened flora, and habitat for native fauna and items of Aboriginal heritage significance. For example, pockets of threatened Downy Wattle and Cumberland Plain Land Snails and a tree scarred by the original inhabitants of the area were found near the proposed gas main route in Deepwater Park. Significant areas representative of Cumberland Plains woodland and dry forest also need to be negotiated.

“Changes have been made to the proposed route in order to minimise potential impacts in these areas. With the help of local Aboriginal groups, artefacts have been moved from the proposed route and the scarred tree has been fenced off and protected. Areas of forest have total exclusion zones and construction activities are closely monitored to ensure minimal disturbance to areas surrounding the construction right of way,” said Mr Sheridan.

“Working closely with a local council has allowed the project to go into similar protected areas and collect seeds and plant stock which is being cultivated to allow areas that had been overtaken by weed and lantana to be regenerated into native bushland during restoration, benefiting the local council and community.”

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

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 Environmental Management Plan was developed for the project, which provides a framework and procedures to minimise potential environmental impacts such as noise, vibration and dust.

The company also introduced a range of different programs, from information displays, to a specific Community Relations team and direct lines of communication with the company to mitigate the effects of construction on the public.

“The project has received positive feedback from the community regarding the swiftness of the construction activities and the extent workers went to minimise the impacts on their daily routine,” said Faye Rescigno, Community Relations Manager.

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

“A typical pipeline will cross one service every 10 km. In the case of the SPL project the main crosses paths with hundreds of major and minor services every kilometre. As such extensive fabrication and pipe bending is 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 require shoring boxes or sheet piling to be installed. Close attention to services searching and extensive pre planning of activities is essential. While a good day on a cross country pipeline is 3 to 7 km, a good day on the SPL is 200 metres between the four work fronts,” said John.

The majority of the construction of the SPL gas main will use 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, very little material can be returned to the trench. This has represented challenges for disposal of vast quantities of what would normally be considered as clean fill.

There are also four horizontal directional drill (HDD) water crossings and twelve significant cased bores under sensitive areas and major road crossings. HDD sites include Salt Pan Creek, Cooks River and two crossings of the Georges River, one at Casula, the other at Panania.

“The Deepwater Park HDD is located in an extremely sensitive ecological area and has had extensive consultation and environmental procedures developed specifically for this site. Cooks River is also a key HDD water crossing on the project, with a number of unique challenges,” said Ms Rescigno.

“First, both ends of the horizontal direction drill are located near heavily populated residential areas and popular sporting grounds unlike the other three water crossings. Additionally, there are existing significant underground assets, and in consultation with the assets owners, Alinta has developed a suite of control measures for this water crossing. Also, the proximity of the neighbouring properties was considered in the layout of the Cooks River drilling worksite, and equipment and machinery were strategically placed to minimise noise and the impact to residents.”

Alinta also examined processes such as HDD long hole technology in order to mitigate the impact on residential areas.

“This process was discarded as not practical due to the high cost and the suppliers were unable to guarantee a successful outcome,” said Peter. “Instead, a 755 Vermeer trenching machine was used to cut a trench through very congested residential areas. These machines are typically used for cross-country pipeline projects. However, the Vermeer has proven to be a practical way to open a trench in built up areas quickly allowing for increased production with minimal clean up required.”

The project management team also designed the pipeline to take advantage of up-to-date pigging tools for internal inspection and cleaning that can deal with pipelines of dual diameters (in this case 500 mm and 550 mm) in addition to small diameter (1.5D) bends used on existing 550 mm section laid in the 1980’s.

“An exercise was also carried out to prove the durability and puncture resistance of the 12.7 mm X42 steel. A 36 tonne excavator was deemed the most credible threat along the route. A 36 tonne Caterpillar excavator using both single and multiple chisel and tiger teeth was used to carry out a number of attempts to puncture the pipe. The pipe was buried to depth and specification. Steel beams and mass poured concrete were used to anchor the pipe for the tests. The excavator was used to attack the pipe at different angles and with different teeth. The pipe was not punctured during the exercise, which validated the choice of pipe material.”

Such consideration also factored in the use of a durable coating for the SPL. The tri-laminate coating (comprised of fusion bonded epoxy, adhesive and HDPE and heat shrink sleeves) proved to be robust enough to minimise minor construction damage. The construction team also made sure to avoid exposed sections of the pipe to reduce maintenance problems due to UV damage to coatings and reduce the potential for sabotage.

“Key staff and construction crews have been specifically chosen with experience working in urban areas. All staff are familiar with environmental controls, traffic control and community relations matters,” said Mr Sheridan.

In early February, the open cut construction was 50 per cent complete. Due to periods of unusually heavy rainfall over the past six months the open cut construction is running slightly behind schedule. The remaining project areas are progressing with completion currently estimated on time.

Given the plethora of obstacles, the on-schedule completion of the SPL is no small feat and will be attributed to successful planning at all stages of the project development cycle, incorporating consideration of technical engineering, environmental challenges and community perceptions. The benefits of the project are also considerable, allowing existing and future areas of Sydney to have a secure supply of natural gas while giving enough capacity to expand residential growth into new areas within the city’s southwestern region.