As urban environments become denser and more populated across the world, public works in these types of environments are becoming more difficult.
Challenges include working in narrow streets and minimising disruptions to residents and business that are affected by the works.
The John Holland-KBR Joint Venture (JH-KBR JV) and Melbourne Water have navigated both of these challenges on a sewer upgrade using a method that helped to deliver the project ahead of schedule.
The Carlton Main Sewer Upgrade in Carlton North and Fitzroy North in Melbourne involved installing a new 510 m sewer and relining around 1.6 km of existing sewers and associated manholes.
The Carlton main was built in 1900 using hand tunnelling techniques, but it was starting to deteriorate and was reaching the end of its life expectancy. It required augmentation and associated asset renewal, which involved installing a new 510-m sewer and relining around 1.47 km of existing sewers and associated manholes.
The Carlton Main Sewer Upgrade also included constructing two 25-m-deep shafts in basalt, supporting operational sewers inside each of the shafts.
The new sewer section was 510 m long under a busy road at a depth of 12 m, and connected the Carlton Main Sewer to the 25-m-deep Merri Creek Intercepting sewer.
As the sewer couldn’t be shut down for the work, everything had to be carried out while it was still operating.
Minimising shafts
In order to minimise disruption to the community, the team reduced the number of shafts that were required for tunnelling operations.
“The original concept involved a small diameter sewer that would’ve required four or five shafts in the roadway. That was redesigned by the JH-KBR JV to a bigger sewer, which meant that we only needed a shaft at either end,” said Andrew Moorhouse, senior project manager at Melbourne Water.
“That minimised the impact to traffic, and it also had a very positive impact on the local community with no shafts in front of their houses, apart from each end.”
While the project utilised established slurry pipe jack tunnelling technology to complete the tunnel excavation works, further improvements were made to these systems to increase efficiency such as the use of small electric trolleys – long, yellow, electric buggies that run on rails in the pipe jack tunnel.
“It was the first time we used them, and that enabled us to basically transfer people and materials up to the front of the machine,” Moorhouse said.
While the original sewer would have been built at a time when there were paddocks and fields nearby, the upgrade took place in what is now a built-up residential area in the inner city.
This meant adhering to strict vibration requirements to minimise the chance of damage to properties.
The team also used prefabricated glass reinforced plastic (GRP) shaft lining systems to minimise safety issues and reduce inconvenience to the community.
“We utilised a liner for 90 per cent of the shaft lining. We maintained the reinforced concrete base purely because of the tie-in details to the Merri Creek Interceptor and because it was the better solution,” said Adam Gorny, project manager at John Holland.
“But what was unique to this job was that it was the first time we’ve gone from top to bottom with the GRP liner.”
This allowed the team to reduce the issues involved with working at heights that are traditionally involved with reinforced concrete construction.
“Obviously, hauling a 14-m-long liner that’s 3.6 m in diameter through the streets of North Fitzroy and Carlton required a bit of coordination. But once it was there, it was a fairly straightforward process. Back-filling it was all done from the surface as well,” Gorny said.
The project also used a GRP liner to rehabilitate a 27-m-deep manhole above live flows in the North Yarra Main in the middle of Princes Street, one of Melbourne’s busiest arterial roads.
“If you did it in a more traditional way, which is repointing the brickwork and spraying a liner ... we’re talking about six or seven weeks potentially,” Gorny said. This methodology ensured the team could maintain traffic flow and minimise impact to the community.
Urban environments
As population densities increase in urban environments, so too does the community’s expectations.
“A hundred years ago, you could go and dig up someone’s front yard and not worry about it,” Moorhouse said.
“Nowadays, there’s no way you can do that … The idea is to try and manage it as much as possible and bring the people along on the journey with you so that they know what to expect and you’re not unduly distressing them.”
This can be a difficult path to tread when residents can feel as though they are living with perpetual public works, from electrical to road works, which has meant stakeholder engagement has become much more important.
But Moorhouse said it’s the little things that can make a difference, such as accommodating a wedding at a church and opening up access to the location, which he said Melbourne Water has done in the past.
The technical challenges of working in modern-day urban environments are also becoming greater.
But Gorny said emerging technology will make sewer work more efficient. For example, mechanised shaft sinking equipment is being readily used overseas to excavate and support shafts on infrastructure projects.
“You’ll see that technology introduced to the market in the not too distant future. It will take one major company to introduce it to the country on a suitable project and people will see the benefits of it, they’ll take the risk and then you’ll find that it gets adopted,” Gorny said.
“You also have to have a client that’s willing to absorb the cost as well. That’s where the change will come.”