In both cases the sewer diameter was upsized using pipe bursting. The ability to increase the size of an existing main without digging and relaying the pipe is one of the major advantages of pipe bursting technology.

South East Water is one of Australia’s most innovative and progressive water authorities and is one of three metropolitan water companies providing retail water and sewerage services to Melburnians. With over $1 billion in assets including over 7,000 km of gravity sewer mains, South East Water has an ongoing requirement for sewer renewals.

South East Water and Kembla Watertech have entered into a partnering contract for the delivery of sewer rehabilitation services throughout the entire South East Water area.

Services provided as part of this partnering contract include sewer relining using Kembla’s solid wall structural EX and Enviro-liner methods, pipe bursting, patch lining, slip lining and localised repairs via the company’s in-house civil works capability.

This partnership has been in operation for five years and over this time has demonstrated on numerous occasions the close fit between South East Water’s needs for sewer rehabilitation and the services provided by Kembla Watertech both in type and capacity.

As part of South East Water’s 2006/07 Branch Sewer Program, two sewer augmentation projects, in Mornington and Dandenong, were completed utilising Kembla’s new static pipe bursting equipment. The objective of both projects was increased sewer capacity.

Mornington Royal Branch Sewer Upgrade

This project involved the upsize of approximately 570 m of sewer which varied in diameter between 300 mm Ø to 375 mm Ø.

The work site was located on the Esplanade in Mornington, a busy bayside outer suburb of Melbourne. The sewer alignment varied between the traffic lane closest to the kerb and the footpath. Although traffic management was required to redirect vehicles, the overall duration of this was reduced significantly by the time efficiency of pipe bursting versus open cut.

A number of environmental considerations needed to be addressed, due to the proximity of the site to Port Phillip Bay, and the relatively shallow depth of the downstream sections of the sewer where bypass pumping was set up.

Additionally, the bypass pumping setup was a considerable distance from the work site, requiring an independent monitoring team. Approximately 300 m of bypass hose was set up, crossing under a main road and several car park entrances.

The host pipe was a 300 mm diameter reinforced concrete with high tensile reinforcing wires. In addition to the reinforcing, the additional concrete thickness at the collars made it difficult to burst.

This project was completed using a Grundoburst 800G pipe bursting unit, and all 88 tonnes of its capacity was needed. In one section of the burst, maximum pulling force was achieved prior to the head stopping. An excavation was required to investigate why the head jammed and it was found that during construction of the host pipe, rock was encountered and only enough rock was broken out to allow the pipe to pass through. Given that the host pipe was being upsized, there was no possibility of ground displacement or compaction to allow the new pipe to be pulled through, causing the bursting head to jam. Once this constriction was removed the remainder of the section was burst without incident.

The tooling used to enable the expander to pass through the host pipe included a roller cutter to first slice the reinforcing, allowing the expander head to open up the host pipe sufficiently for the new larger diameter HDPE pipe to be pulled into position.

The close proximity of an asbestos cement water main and a gas main at various points along the alignment was also a concern. The risk of damaging these assets was greatly reduced using static bursting versus pneumatic bursting, however mitigation of this risk was still required.

To ensure that adjacent customers did not incur a water supply interruption, South East Water decided to also renew the water main at the completion of the sewer augmentation. The water main was taken offline by placing adjacent customers on a temporary water supply.

Despite the difficult work location, hard ground conditions and proximity of other assets, this project was completed prior to the busy summer holiday period and the outcomes created greater sewer capacity, thus increasing the sewerage systems ability to cope with increased flows over the summer holiday period.

Dandenong Branch Sewer Upgrade

This project involved the upsize of approximately 416 m of PE pipe, varying in diameter from 375 mm Ø to 450 mm Ø. The work site was made up of two sections - the first located through backyards and a residential street, and the second on Shepley Oval, the host of the Victorian Cricket State League pennant semifinal.

One of the issues faced during the latter parts of this project was the cricket semifinal, scheduled for the weekend following completion of the project. Site restoration to a standard suitable for such an important event was a critical component of a successful outcome.

Significant bypass pumping was also required for this project with bypass pumps set up away from the work site and bypass hoses running across public open land adjacent to Dandenong Creek.

Due to the concrete host pipe being reinforced with high tensile steel, it was determined that the Grundoburst 800G would not have sufficient capacity to complete this project.

With the assistance of Peter Decker from TT Asia Pacific, Kembla Watertech was able to trial the use of a Grundoburst 1250G unit. The Grundoburst 1250G has 125 tonnes of static pulling force. This project was the first time a static pipe bursting unit of this size has been used in Victoria.

In contrast to the project in Mornington, the use of this larger pipe bursting unit required an increase in capacity of most of the associated equipment. Larger excavation equipment was used, larger shields were used, larger excavations were required and additional time to burst was required due to the logistics of setting up and using the physically larger equipment. In this case – size did matter!

The average depth of sewer for this project was approximately 5.5 m, however with the additional pipe bursting capacity, depth was not an issue.

The tooling setup used on this project was identical to the Mornington project, apart from using a larger cutting wheel set (300 mm versus 375 mm diameter host pipe) on the roller cutter and larger couplings to adapt to the larger 1250G rods.

The pipe bursting unit operated in exactly the same way and the same process was followed to complete the upsize of this sewer.

Once again, a successful outcome was reached by achieving the prime objective of an increase in sewer capacity while at the same time managing environmental risks and minimising restoration issues and completing the project within planned timeframes.

In summary, both of the above pipe bursting projects highlighted the advantages of undertaking large complex projects within a partnering contract environment. The strong support between the contractor (Kembla Watertech), the asset owner (South East Water) and equipment/technical supplier (TT Asia Pacific) was paramount to achieving the project objectives.