After a series of incidents in which loose concrete fell from Ottawa's St-Laurent LRT station last year, CBC News has learned more details about how the city is addressing chronic water infiltration in the former bus tunnel, including fixing leaky joints — some of which had passed their life expectancy.

According to engineering reports, some of those joints had not been replaced in nearly four decades — including in areas where concrete chunks fell onto the train tracks in January 2024.

CBC has also learned of an ongoing leak near another tunnel joint, which the city said it hopes to address next year.

The tunnel, which was built for buses in the 1980s before being repurposed into an LRT station, has been suffering from water leakage for decades.

Last spring, city officials couldn't say what was causing the persistent leaks, which are deteriorating the concrete by causing "delamination" and "spalling" — when concrete pieces break off the main slab.

During planned maintenance this month, the city plans to further inspect the tunnel, scale down more loose concrete and address other issues identified during the 2024 Ontario-mandated inspection — a regular checkup that was largely skipped in 2022 due to major construction at the bus station above the tunnel.

In 2018, a year before the LRT station opened, two engineering firms investigated and laid out multiple possible sources of the leaks. They also suggested potential temporary and permanent fixes, according to reports CBC obtained through a freedom of information request.

According to a report by engineering firm Morrison Hershfield, the tunnel's expansion joints appeared to be a hot spot for water infiltration, damaging the concrete and ceiling framing and corroding pipes.

Expansion joints connect concrete sections of the tunnel and contain flexible material such as a sealant, allowing the structure to contract and expand with temperature changes and other factors.

Without properly working joints, stress from those fluctuations can cause cracking and leaks, compromising the durability of the concrete.

"Joint intersections are common sources of water leakage due to the difficulty of manufacturing a continuous … seal," reads the report.

The estimated life expectancy of an expansion joint is 15 to 30 years, while the seals themselves are expected to last five to 15 years, according to the report, which cites a manual from Ontario's Ministry of Transportation.

While six joints in the St-Laurent tunnel were replaced in 2009, two others identified in the report as joints G and H hadn't been replaced since 1986. When the report was compiled in 2018, these two joints were already 32 years old.

"It is noted, however, that these joints are not leaking as severely as [others]," the report states, rating them in "fair operating condition."

But by 2020, an inspection found water had been actively leaking from Joint G.

"Majority of expansion joint seals are leaking," reads the provincially mandated inspection report obtained by CBC.

The city said joints G and H were finally replaced in 2023. By that time they were 37 years old, well past their life expectancy. Then, in January 2024, concrete chunks fell onto the tracks below joint G.

That May, concrete debris was found to have "disrupted" ceiling tiles above passenger platforms, and more loose concrete was discovered in October, once again halting LRT service at the station.

If it's performing, why take it out?- Susan Johns, director of asset management

After that May incident, an internal city email revealed staff had again "found extended delaminated area at expansion G over the track."

According to the city's director of asset management Susan Johns, replacing the joint didn't address the leakage problem.

"When the expansion joint work was completed, which should eliminate leaking, there was still leaking," Johns told CBC.

Crews then found a "new source of water," Johns said — drainpipes in the tunnel roof were cracked and leaking, including over Joint G. This has now been fixed, Johns told CBC. 

Regarding the life expectancy of the joints, Johns said the city monitors its structures regularly and prioritizes replacement based on performance. 

"If it's performing, why take it out?" she said.

In addition to replacing all the expansion joints at the St-Laurent station, engineering firm Paterson Group recommended in 2018 installing a new permanent membrane to waterproof the concrete slab above the tunnel.

"Once the permanent solution is in effect, it's expected that most of the leaks within the St. Laurent Station would be reduced significantly," the report concludes.

The city told CBC partial waterproofing of the roof slab was done during the 2023 repairs, as well as plugging some utility ducts and electrical boxes. 

Remaining work to mitigate leakage, including more waterproofing and replacing outstanding sections of expansion joints, is scheduled for 2026 and 2027, the city said.

There's also an outstanding leak near expansion Joint D, the city added. It's now being investigated and will be fixed during the 2026 project.

Despite these ongoing issues, Johns said the tunnel is safe.

"It's in very good condition. It does not pose a risk to our passengers, to our staff or to our trains," she said.

"We need to avoid, as much as possible, water from concrete structures," said Leandro Sanchez, a concrete durability expert and engineering professor at the University of Ottawa.

Asked about the lifespan of expansion joints, Sanchez explained that if they're not properly maintained they can become more rigid, allowing water to seep through and cause further deterioration.

"Then you start having durability-related issues," he said, adding photos of the station published by CBC showed signs of that.

Sanchez agreed that performance, not age, is key to determining the viability of an expansion joint.

"But you know, all of the materials, they have some lifespan — all of them, including concrete. And the harsher the condition, the lower the life expectancy," he said.

Sanchez stressed regular assessments, as well as early rehabilitation and maintenance, are "really, really crucial" when it comes to concrete tunnels like the one at St-Laurent.