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Bennelong Sewer reline – as big as it gets

Kembla Watertech recently took out the ASTT Rehabilitation Project of the Year Award for their innovative CIPP rehabilitation of the Bennelong Stormwater Channel on behalf of client Sydney Water.

Rehabilitation of this centuries-old system may have been the largest diameter CIPP installation in Australia – and one of the largest inversions ever in the world.

The project was significant because of the age of the system that was rehabilitated (more than 150 years old); the fact that it was the first oviform combined sewer/stormwater system constructed in Sydney; the density of the population surrounding it; the enormous size of the channel (perhaps the largest diameter CIPP lining installation ever conducted in Australia); the thickness of the liner (35 mm); and the fact that it involved one of the largest oviform inversions ever worldwide.

The project was completed in June 2012. Around 154 m of a massive 1,830 x 1,220 mm heritage-listed oviform stormwater channel was rehabilitated for Sydney Water. The pipe was relined in two inversions using CIPP installation. The access chambers had to be specially constructed for this installation, located in the middle of Sydney CBD bus lanes, near bustling Circular Quay.

The liner was installed from an access chamber in Phillip Street, which is in the middle of Sydney’s CBD. The site was surrounded by major businesses, a five star hotel (the InterContinental), and was in the middle of a major bus route in downtown Sydney.

This is the largest diameter CIPP lining installation ever conducted in Australia and one of the largest oviform inversions worldwide. It was an extremely difficult and labour intensive installation due to the sheer size and thickness (35 mm) of the liner.

Challenges faced on this project included the close proximity to residents, hotels, tourists, businesses; the proximity to Sydney’s popular tourist location Circular Quay; the physical size of the liner to be installed; the fact that the location intersected with major downtown Sydney bus routes; and the fact that the asset being rehabilitated was Heritage-listed.

Lining installation

Kembla Watertech used a CIPP water inversion installation. With such a significant stormwater pipe diameter, and a 1,550 mm diameter liner weighing 15 tonnes, it was an extremely difficult and labour intensive process of installation. A stormwater bypass, including construction of a brick weir, was required because of the high residual flow. Ramps over the bypass hose needed to be constructed with enough strength to withstand the high volume of bus traffic encountered in Phillip Street. The layover lane was diverted to a separate location to allow for site establishment and to conduct the work properly.

Access chambers needed to be constructed specifically for the installation of this liner, so that the equipment and liner would be able to fit inside.

The liners, manufactured by Applied Felts, were installed in two inversions, both from Phillip Street. The first installation was conducted from Phillip Street to Albert Street, and the second installation was in a high risk upstream direction from Phillip Street to Young Street. This involved increasing the head pressure and scaffolding tower height in order to correctly invert the liner against gravity. There were also risks with loss of temperature to cure the pipe due to circulation difficulties while lining in an upstream manner.

Normally the second installation would be conducted from Young Street, however, the location of the access chamber in Young Street and the amount of roadway available for working made this an unsuitable option. Close discussions with the Roads and Maritime Services (RMS) and Sydney Buses resulted in Phillip Street being chosen as the preferred option for the inversion location. The work was completed successfully with no incidents.

Novelty of technology

There are two unique parts to this lining installation. Firstly, Kembla Watertech utilised a one-of-a-kind wet out conveyor system; and secondly, the size of the liner made it a remarkable installation.

Kembla Watertech invested over $A200,000 in a new CIPP wet out conveyor system that could handle the sheer size of this liner. The wet out conveyor system took six months to purpose-build and takes up most of a large industrial warehouse in Sydney’s southwest.

This installation was the largest diameter and thickest CIPP lining inversion ever conducted in Australia and one of the biggest worldwide, coming in at 1,550 mm diameter (to fit the 1,830 x 1,220 mm pipe with a wall thickness of 35 mm). It took significant physical labour to manoeuvre and install inside the pipe.

Environmental and community benefits

The Heritage-listed Bennelong stormwater channel was built in 1857. It is the first oviform sewer to be built and one of five original combined stormwater/sewer systems built in Sydney at the time. These channels improved public health, hygiene and living standards immensely for the people of Sydney.

The site was less than 100 m from Circular Quay, Sydney’s popular tourist hub, and close to historic districts. Circular Quay hosts the ferry terminals and a main CBD train station. Surrounding the site were high-rise business and residential towers, and the five star Intercontinental Hotel.

Due to the amount of vehicles required for the job, Kembla Watertech utilised the bus layover lane in Phillip Street as part of the work zone. Buses had access around the zone, and the layover was relocated to a different street. This required significant consultation with Sydney Buses management.

Traffic impacts

Stakeholder discussions were held early on with the surrounding businesses and residents to ensure everyone was informed of the impacts from the work. Phillip Street experiences a high volume of traffic, so traffic control was staffed 24 hours a day and managed closely so that traffic flowed smoothly.

Occupational health and safety benefits

The benefits to the wellbeing and safety of the workers and general public that cross paths with trenchless projects are numerous.

The reduction of open excavations using a lining project as opposed to an open cut technique so close to a public location was a huge benefit to community safety. Risk assessments and consultation with all affected authorities ensured adjacent infrastructure was protected along with the wellbeing of the workers.

Constructing the purpose-built wet out bed, which was predominantly there due to the sheer size of the liner, had the separate benefit of reducing the physical labour required during the wet out process, thereby protecting the safety of the workers.

Project outcomes

Rehabilitating the Heritage-listed Bennelong stormwater channel was a major achievement. Kembla Watertech was honoured to be part of the rehabilitation of such an important historical asset for the community. The officers conducting environmental and heritage assessments, and the workers who were able to enter the access chambers were struck with a sense of awe at the engineering and construction methods used more than 150 years earlier.

Notwithstanding the heritage significance of this asset, the skill required to install a liner of this size is a major feat for Kembla Watertech. To have inverted the largest oviform liner in the southern hemisphere requires intensive planning, skill and physical labour of great proportion, and it was done successfully and to plan.

This was a major accomplishment for Kembla Watertech, particularly considering the in-depth stakeholder and environmental planning that was required for this project, and its location in the heart of Sydney.

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