Manhole rehabilitation for Tweed Shire Council

Manholes reaching the end of their lifespan pose an ongoing challenge for councils and water authorities across Australia and New Zealand. What’s the big problem? Over time, the gases in manholes can cause hydrogen sulfide (H2S) corrosion, leading to concrete cancer and degradation. This in turn makes the manhole susceptible to groundwater infiltration – which puts added pressure on the whole system.

Often, councils choose to rehabilitate manholes progressively rather than all at once, because there are so many throughout most urban cities. This was the case in New South Wales’ Cabarita Beach, where earlier this year a new development of residential apartments was in the works.

They needed to connect the development to three manholes in the construction process. As part of their development application with the Tweed Shire Council, they were required to upgrade the existing manholes to prepare them for the additional load of the new homes.

THE PROBLEM: MANHOLES NEEDED TO BE REHABILITATED WITHOUT PUTTING CONSTRUCTION ON HOLD

The construction contractor was keen to find a solution for upgrading the manholes that didn’t mean putting the rest of the project on hold because of excavation. As well as delaying the construction time, excavating would have required a wide trench to be dug up, with shoring boxes, impotent water infiltration areas and a spear point to get rid of the excess water. These types of projects usually run into the tens of thousands of dollars to complete – not to mention the disruption to roads and pedestrians.

The construction contractor had previously heard of Nuflow’s manhole rehabilitation solution, and reached out to the Nuflow Gold Coast team to see if they could help. Nuflow Gold Coast and Nuflow’s Research and Development team joined forces on this project to assess the manholes and create a completely custom-made solution for structurally rehabilitating them.

THE SOLUTION: STRUCTURAL REHABILITATION WITH MINIMAL DISRUPTION

The three manholes were located in the nature strips on either side of the busy road, with two of the manholes at a depth of 3 metres and the other 1.2 metres. The team set up their perimeter and got to work.

“We didn’t need to disrupt traffic or use traffic control because of the small footprint we have on the ground when we rehabilitate manholes.” – Ben, Nuflow Technical Development Manager.

First up, there were about 20 metal ladder rungs that had to be removed – due to new regulations designed to prevent people from climbing down into manholes. To create a safe environment for grinding off the ladder rungs, the team first used a vacuum fan to draw out the H2S gases.

For the two deeper manholes, a structural liner – Nuflow’s Sumoline – was installed from the base of manhole right up to the manhole cover. For the third, shorter manhole, a trowel-able epoxy solution was used to provide a structural coating.

The solutions used across all three manholes provided a seal not just against leaks, but also against H2S gases.

“With the mixture of the water and the gases in manholes, it creates hydrogen sulphite which causes the concrete to break down, which we call concrete cancer. When we put a structural liner and coating over the top, this is impervious to the gas and can put a stop to this degradation.” – Ryan, Nuflow Team Leader Research and Development.

All up, the job took less than four days to complete, with minimal disruption.

“Because of our small footprint on site, and because we didn’t need to excavate, the construction team could keep working while we repaired the manholes. They were happy they didn’t need to delay the project.” – Jayden, Nuflow Gold Coast Reline Manager.

MANHOLE REPAIRS SORTED WITH NUFLOW

If your manholes are reaching the end of their lifespan, or you want to protect against future degradation, your local Nuflow team can help. Find your local pipe relining experts and chat with the team to learn more.

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