Ontario Construction News staff writer
William Coleman had a contractors’ nightmare.
He was a construction manager responsible for tunnels and shafts of the first phase of Ottawa’s Light Rail Transit (LRT) project – and major leaks were plaguing the underground tunnel in Ottawa’s core before its completion in 2019.
Soil conditions and the working environment were challenging: At one point in 2016, a sinkhole opened up on Rideau Street, sucking in a parked locksmith’s truck, flooding 300 metres of tunnel.
The leaks, some modest, and some that at times were torrential downpours, needed to be solved, but how?
In the end, after trying seven options in a seemingly futile – and expensive – search for answers Coleman says he found a solution that has proven to be inexpensive, easy-to-implement and sustainable – and is now providing the framework for waterproofing the massive Parliament Hill renovation project.
Coleman, currently the structural lead for the Ellis-Don/PCL consortium working at the Centre Block, told his story of trials, tribulations and ultimate salvation at Building Envelope Council Ottawa Region meeting last Wednesday (March 20).
Things began going wrong when contractors started boring tunnels and digging shafts for the LRT’s underground line, he said. Work needed to be completed in a downtown environment with many underground utilities, services, and neighbouring buildings. The solid bed rock conditions made for slow tedious excavation work and ground water was being controlled by typical construction pumping.
Underground stations and tunnels along the LRT line represented what had been the deepest below-ground structural work in the city’s history – and water started pouring into the tunnel near project completion; creating a crucial problem that needed to be solved, permanently.
Coleman says his team began casting for solutions. Various vendors offer a diversity of waterproofing solutions, and he tried them one, by one. Each involved various contractors and material suppliers.
In his presentation, Coleman avoided naming the eight various brand strategies or systems, but many of them are well-known proprietary commercially available products. Coleman clarified that there are many products available to the market but from hands-on practical discovery all are not suitable for every water leaking condition. He describes the challenge as finding the appropriate tool from the tool box for the specific task.
First try: Polyurethane 2-part injection
This didn’t work at all. It stopped the leaks for a short time, if at all. Part of the problem was the “high wick effect” – the sealant would simply absorb the water and as more water poured in and the leak ultimately overloaded it.
Second try – Polyurethane two-part injection with additives
In this case, the supplier offered an acrylic additive to be pumped in after the polyurethane to fill capillaries and stop the wicking effect.
“This stopped the water instantly, but it cracked over a few weeks with no additional water-stopping ability,” Coleman said. And the second, ineffective solution, was more costly.
Third try – Higher density two-part polyurethane
This appeared somewhat successful at grades less than four metres or 13 feet deep. But the solution didn’t last. The sealant cracked and leaks resumed, and this was again relatively costly.
Fourth try – Cement base crystalline
Coleman said this low-cost surface application simply didn’t stop the leaks. A surface positive site application was no challenge for these below grade structures and merely served as a short term band aid holding water in the structure before allowing it to bleed.
Fifth try – Hybrid polyurethane/cement
“It worked in the tunnel, for about 30 days,” Coleman said. Because the sealant was very rigid, it ultimately debonded and cracked due to shrinkage by “head pressure and movement,” thus failing to stop the leaks. It was moderately expensive.
Sixth try – Acrylic gel
This option resisted the wick effect, but became “very dense and brittle over time” and could only be counted on holding for 15 to 20 days.
Seventh try – Friction activated latex rubber
By this point, Coleman described a sense of desperation after the multiple failures. He was ready to try a product developed in South Africa that had been modestly used before in Canada. And it worked – finally stopping water on smaller cracks for at least a year or two.
Unfortunately, the solution didn’t succeed in stopping leaks from larger cracks. “The sample in the office became very stiff and is no longer elastic,” he said. “The product did not work on larger non-localized leaks.” More painfully, it was messy. The sealant spread everywhere, including into underground areas of neighbouring buildings.
Finally, Coleman learned of another solution that also used rubber, but combined different compounds into a single component gel, delivered in blocks to the construction site, and then melted temporarily with specialized heating equipment. Once injected, the compound filled the cracks, then cooled into a permanent but flexible non-curing rubber seal.
“This stopped water in all the areas, including small and large cracks long-term,” he said. “The first injection was in March 2020 and is still holding.” There is little to no cleanup, and the low-cost solution is still holding up well several years later.
Coleman said he took these lessons and learned concepts when he moved with EllisDon to work on the Parliament Hill renovation.
With experience, the contractor didn’t need to go through the same learning curve to create a watertight foundation design suited to the special conditions and challenges of the Parliament Hill restoration.
“The new waterproofing design will integrate a non-curing self healing rubber gel that is heated and then sprayed onto the foundation walls. known as poly rubber gel,” he said in follow-up notes to Ontario Construction News.
As it doesn’t need any curing, work can be done quickly in all weather conditions, and there is no need to slow the project.
The product is sustainable, as it is largely made from recycled tires and is not a byproduct of the oil and gas industry. It is designed with waterproofing in mind.
Coleman indicates that the blame for the LRT foundation leak problems could be attributed to several causes; including the general contractor’s failure to ensure proper trades guidance and quality assurance; designers in failing to specify suitable products for the site conditions, suppliers in asserting their product is suitable for “all conditions” and sub-trades who may have taken short-cuts or failed to follow the processes required to follow complex supplier installation instructions.
In the end, after eight tries, the poly rubber gel has succeeded because it is a simple one-part injection technology, non-curing (thus maintaining flexibility and elasticity), has a medium viscosity (so didn’t run all over the place), fully bonds to wet or dry concrete, truly dams the water even in areas where it is difficult to see or access the leak, and where there is no material waste, Coleman said.