Water Street 'big dig' ditched for trenchless method: Here's how it will work

The City of St. John's has abandoned plans to dig up Water Street to replace the aging pipes underneath in favour of a trenchless approach — but how exactly will that work?

Trenchless technology will save city money and be less disruptive, says Danny Breen

Geoff Bartlett · CBC News · Posted: Jan 25, 2017 9:34 PM EST | Last Updated: January 26, 2017

This diagram from an American project shows roughly how the trenchless method works. Two holes are dug to access the pipes underground, and an epoxy resin is fed through which coats the inside of the old pipes. Once the resin hardens, it reinforces the pipe. (Twitter)

The City of St. John's has abandoned plans to dig up Water Street to replace the aging water and sewer pipes underneath in favour of a trenchless approach — but how exactly will that work?

Trenchless technology involves replacing or reinforcing underground pipes without having to dig up large areas of the street to get at and remove them.

In some cases the existing pipes are destroyed and replaced, but for the Water Street project – set to begin in 2018 – the plan is now to reinforce the existing pipes by filling them with a plastic-like material called an epoxy resin, which will then coat the inside and harden to form a new lining.

Water Street infrastructure project delayed

8 years ago

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The big dig on Water Street has been delayed until 2018, where much of the work will be done using "trenchless" technology.

Coun. Danny Breen said the approach is not only less disruptive to businesses and traffic than the original plan, but will cost 25 to 30 per cent less than traditonal replacement, and should last for at least 40 years.

Unusual pipes

Trenchless technology was used in the city before — on Wishingwell Road and in Shea Heights — and Breen is confident it will work on the old stone sewer pipes downtown as well.

The existing century-old sewer pipes under Water Street, like the one shown here, are made from stone and are egg-shaped. The City of St. John's said this could create unique challenges for the trenchless method but is confident it can still be done.

"You're keeping the outside stone pipe, as that provides you with the support. Then inside it you have a new pipe," he said. "It will last. It's been tested. It's durable and it's been done in other places, so we think it's the best solution for everybody."

Breen said the existing downtown pipes are unusual as they are egg-shaped and made from brick, but after some research it was determined that the trenchless method would still work on them.

In fact, he said the new lining will actually stop ground water from seeping through the brick pipe and going into the pipe's flow — water which then needlessly ends up being processed through the city's sewage treatment plant.

Holes on side streets

While there are no plans to dig right on Water Street itself, there will still be holes dug to get at the pipes. Baird's Cove and other connecting side streets will be excavated. Breen said vehicle traffic will still continue to flow but with some delays and detours at times.

"It has to come down to the individual businesses and their requirements during the project to make sure that we minimize the disruption to their businesses," he said.

Infrastructure in downtown St. John's is aging and needs to be replaced, so the city is now looking at reinforcing water and sewer pipes by using a trenchless method. (Twitter/@DowntownStJohns)

Breen said the plan is to start working on the west end of Water Street, and then move east, city block by city block. With underground infrastructure that is more than a century old, the city is aware there may be some unusual things to deal with along the way.

"I'm sure there's going to be challenges as we move through it," he said.

"But both our engineering staff and our consulting engineers – along with the experts in this type of engineering technology – are confident that this is a good procedure."

While there is no plan to dig on Water Street, there will still be holes dug on side streets such as Baird's Cove, so that contractors can access the pipes under Water Street. (Google Maps)

Breen said the work is delayed until 2018 to give the city, businesses, engineers and consultants time to figure out how to best phase in the work. The first step is to have the contract go to tender, but he expects even when the work starts it could take several years before all the pipes have been reinforced.

The video below demonstrates how the trenchless method works on a residential property: