It was no small task. Totalling 67 metres, the two sewer pipes identified as part of a bundle of urgent works for rehabilitation by Sydney Water, exceeded the distance of the longest kick in most football codes including the AFL.
Adding to this daunting subsurface scale, the pipes were situated beneath a tourist hotspot in McMahon’s Point.
Disruption would have to be kept to a minimum with adjacent apartment towers and a busy road recognised during early pre-planning as constraining factors given the proximity of residents and traffic.
Relining bundles on the Sewer Stormwater Rehabilitation Program, often condensed into the acronym SSRP, are ongoing and help to ensure Sydney Water meets its operating and environmental protection licence requirements by preventing dry weather sewer overflows according to Kevin Barry Project Manager at Confluence Water.
“The main project objectives are to reduce negative impacts on the customer and the environment while minimising ongoing maintenance costs of the selection of sewer assets in the northern Sydney areas,” he said.
Confluence Water is part of a joint venture consortium on the NEC4 Engineering Construction Contracts, Partnering for Success (P4S) working in collaboration with Sydney Water on the northern district, a vast metropolitan area that spans from Blacktown to Palm Beach.
Over the past 20 years rehabilitation works on the wastewater network have been largely ad hoc with different techniques and methods such as spray lining, CIPP and a variety of moulds employed to reline the insides of the pipes.
“The main problem with the sewers is the tree roots that ingress into the joints of the gravity sewer pipes which were laid in Sydney decades ago,” said Barry.
“In some cases, as far back as a century ago.”
Confluence Water determined that renewing the pair of pipes at McMahon’s Point was a priority based on a condition assessment.
Pipeline infrastructure specialists Interflow, a long-time partner of Confluence Water and Sydney Water, were engaged on the project which officially commenced onsite last September, following substantial preparations that included a condition review of the host pipes.
Any available CCTV footage was reviewed and the design phase began in earnest according to Sunny Singh, Interflow Project Manager.
“From there onwards we carried out a design for the liner profile,” he said.
“We chose the Expanda product and the primary reason for that was the fast installation times it was going to deliver and its significant structural strength.”
Expanda, a full-bore structural liner, uses a spiral wound interlocking PVC material that expands to fit tightly against the host pipe.
Installed by a mechanical process, there is no need for heating or temporary softening of the liner. Expanda can accommodate diameters up to 1200mm.
The pipe is basically a new pipe inside of an old pipe that can, what’s more, remain live throughout the whole installation process, reducing the need for disruptive and sometimes destructive bypass works.
“We were able to carry out the rehab work within roughly one day of lining which is all it took for us to renew these pipes. Whereas if you were to dig up a 67-metre pipe and carry out this operation by trenching, you would be looking at approximately three to four weeks or even more. This would include significant community disruption, a lengthy excavation, moving heavy machinery, noise and additional health and safety hazards that you would introduce to the site — all of this we want to avoid,” said Singh.
“Expanda reduces all of that. After the pipe is cleaned and inspected, the crew sets up the site at each end of the asset at existing access chambers, winds the profile through, expands the profile, cuts the junctions, secures the ends and you’re out. A smaller team then comes in to seal the junctions and complete the job.”
Insofar as a pipe with a diameter of 225mm certainly holds a lot of sewer flow, Expanda also allows Interflow to work in live flows, a significant benefit as the crew can plug and release the flow, as it sees fit in accordance with the Flow Isolation and Flow Management Plan, a Sydney Water process, without having an impact on the liner or its machinery in situ.
This way Expanda reduces planned labour and site setup requirements as well.
It’s also less disruptive to community given Interflow doesn’t have to establish bypass pumping.
As a result, the inconvenience of having to divert the flow from an upstream manhole is avoided.
“We know these manholes can be two to three metres deep, maybe more in some places because it is all gravity fed,” said Barry.
“So that was another benefit of the trenchless technology.”
In this particular instance Interflow did not require flow isolation.
The mechanical, trenchless design affords Expanda a versatility that eliminates the need for excavation, harmful resins, and curing times.
This allows the continuous uPVC liner to easily adapt to different pipe shapes, navigate live flows, and function in hard-to-reach areas effectively thanks to an instantaneous curing time achieved through pre-formed thermoplastic materials.
“There’s no cure time required for Expanda,” said Singh. “What’s more, we are able to handle the many different conditions that we find in a pipe because in most cases it doesn’t stop us. It doesn’t need to be in perfect condition for us to line it.”
By November cleaning and lining had been completed. Interflow then sealed the junctions for any connections coming into the pipe.
Planning and preparation often consume the most time going into a job according to Singh.
“Planning on site is probably the biggest part of it because the lining component is relatively quick,” he said.
“Because you’ve done all the right things upfront and you’ve planned it so well and when you go to site chance of failure is very low. The planning and site set up definitely takes a longer time than relining of the pipe.”
By early December Interflow had closed off the job with seals and a CCTV survey. No night shift was warranted.
“Because they could carry it out under live flow conditions works were completed within the standard working hours,” said Barry.
“They eliminated any need for extensive excavation which significantly reduces noise, traffic impact and overall disturbances to the two apartment blocks that are right beside it. There were no customer complaints on that particular job which was good to see.”
The job was completed essentially in three work shifts, a brief duration impossible to replicate under conditions where the asset has had to be excavated.
Logistically, there were other challenges prone to navigating tight streets and tight spaces which curtails the type of equipment that can be moved in and out.
“We have to ensure we are working safely with the public all around us,” said Singh.
“We needed to have all the approvals in place to do the job safely like traffic control permits and setups. We had to issue community notices which we do as part of our planning processes. We provide notice to people to let them know we are coming to do work in the area. That is all taken into account.”
Barry acknowledged the professionalism displayed by the team at Interflow.
“They are a good team to work with,” he said. “All this trenchless technology is very cool. You really have to see it on site to get your head around it.”
Confluence Water protected sensitive areas in the nearby environment of the worksite such as a bollard at Blues Point Reserve, an historic waterfront reserve at the tip of the peninsula with significant harbour views, a foreshore shelf, and a World War 2 observation post with stanchions and stairs.
“The team did a fantastic job of ensuring that our setup was nowhere near any of the identified heritage items and when we left site we left it as we found it,” said Singh.
“If you go there today you won’t even know there is a pipe running underneath that has been relined or that anyone was there attending site.”
For more information, visit interflow.com.au
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