Taking place in Sydney’s inner west, in the suburbs of Balmain and Rozelle, Abergeldie Watertech’s CIPP lining solution had to overcome the challenges of the sewer’s brick oviform structure and large bends.
The Balmain South Eastern Slopes Submain (BSESS) is a historic Sydney Water oviform brick sewer constructed in 1897. Sydney Water CCTV investigations and assessment of the BSESS identified that 630 m of the 990 mm by 660 mm pipe sections was nearing or had come to the end of it’s service life.
The system was experiencing significant dilapidation arising from settlement and displacements, root intrusions, and erosion of the invert that led to the formation of structural faults in the submain. Maintenance hole structures servicing the oviform submain also displayed structural damage, corrosion, and delamination of render from the maintenance hole walls, increasing infiltration from the local elevated water table.
Sydney Water’s SewerFix program was established to protect public health and the environment by improving its wastewater system. The program includes rehabilitating large corroded pipes, fixing leaks and blockages, installing new assets, and upgrading pumping stations.
The utility determined that the only viable, cost-effective option for the project was the use of Trenchless Technology to install structural internal liners, and it contracted Abergeldie to complete the works.
The challenge
The BSESS rehabilitation project provided a unique challenge for trenchless rehabilitation. The cured-in-place pipe (CIPP) application needed to overcome the following asset characteristics:
- Oviform shaped pipe
- Brick construction in tunnel
- Horizontal curved radius (changes in direction) in the asset
- High water table
- High density suburb with narrow streets.
These characteristics offered a new challenge for CIPP lining and presented a high-risk scope of works with potential for failure without careful planning, smart engineering and vigilant field execution.
Shaping up to be difficult
The brick oviform structure usually relies on the compressive external soil forces to keep the structure solid and are typically very strong in this compressive state. However, the integrity of this egg-shaped structure relies on each brick in the structure maintaining its position; if a key brick is dislodged, it can cause failure of the entire structure.
Traditionally, CIPP liners apply internal pressure during the installation process to achieve a tight-fitting finish in the shape of
the host pipe. In the case of an oviform shape these installation pressures are greater than for equivalent circular pipe installations, with liners relying on the support of the host pipe to maintain its shape until cured.
Applying this pressure to a brick oviform pipe structure has a high risk of collapse if not correctly executed. It was calculated that the pressure required to install a structural CIPP liner in the tunnel has an increased risk of dislodging bricks and preventing successful rehabilitation.
Abergeldie’s solution to reduce this risk of pipe collapse was to install a sacrificial UV cured glass-reinforced plastic (GRP) liner before everting the water cured structural liner. The GRP liner is pulled into position and inflated with air pressure, applying a much lower tensile force to the oviform pipe.
Once cured, the GRP liner provides a temporary structure offering tensile shielding of the brick structure while secondary structural liner is everted using water pressure.
Braving the bend
An additional challenge involved rehabilitating 115 m the brick oviform tunnel, where a change in direction of more than 100° occurred from the upstream to downstream maintenance hole.
The UV cured lining installation process is not suited for these types of bends, as the UV liner is not flexible so would wrinkle on the bends without taking the shape of the host pipe. Furthermore, the cable of the UV light train would drag and cause inflation problems, and the UV light train would provide uneven light intensity in the bend leading to uneven curing.
After much deliberation, Abergeldie decided to use a thinner standard sacrificial CIPP liner. While UV cured lining has the advantage of CCTV camera confirmation that the lining is tightly in place before curing, in this particular case it was decided that the much higher risk option of a standard CIPP liner had to be considered.
The CIPP lining was designed using short-term properties capable of resisting the water pressure and the brickwork load.
This standard CIPP lining would be able to negotiate the pipe bend and enable the installation of the second long-term structural liner. Although the word ‘sacrificial’ has been used to describe the initial UV and CIPP linings, in reality, these linings will have a life after their initial purpose is complete. Although not taken into account in the long-term design, these liners do provide an additional contingency factor in the long-term life of the structure.
Executing the plan
In March 2016, Abergeldie successfully rehabilitated the 115 m curved asset by installing a 12 mm CIPP sacrificial liner, and then installing a 16.5 mm structural CIPP liner. With the careful planning and execution, both liners were successfully installed without any displacement of bricks or damage to the oviform structure.
The remaining oviform sections of tunnel were also successfully lined using UV cured GRP linings, followed by an installation of a thicker structural CIPP liner.
On completion of the works, all parties involved within the contract were satisfied with the positive results achieved in the rehabilitation of the Balmain Submain. Abergeldie successfully rehabilitated assets previously deemed unable to be rehabilitated using traditional Trenchless Technology.
Abergeldie’s execution of the project offered a number of environmental, occupational health and safety, and community benefits. This includes having a reduced site footprint and excavation, achieving no reportable safety incidents, and having less impact on the community, despite operating in a high-density commercial zone.
The success and delivery of this project is attributed to the close working relationship Abergeldie developed with the Sydney Water Delivery Management team, Leichhardt Council and the local community.
This article was featured in the December edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Abergeldie website.
If you have a project you would like featured in Trenchless Australasia contact Journalist Chloe Jenkins at cjenkins@gs-press.com.au