710 litres of grout pumped into leaky LRT tunnel walls

More than 700 litres of grout had to be pumpedbehind the walls of Ottawa's light rail tunnel east of Rideau station last weekendas Rideau Transit Maintenance (RTM) triesto stop water from leaking in.

The move filleda "void"behind the walls at the tunnel's ceilingat the site of apersistent leak,but the contractor expects to work on sealing other trouble spots in the weeks to come, according to an update Thursday at the city's transit commission.

The goal is to solve water problems in the tunnelonce and for all, said transitgeneral manager Rene Amilcar.

Ottawa's Confederation Line was partially shut down for the past two weekends so maintenance workers couldinvestigatewhy the tunnel's waterproofing wasn't working as intended.

RTM ended upinjecting about seven bathtubs worth of grout into one specific area on the ceiling of the tunnel east ofRideau station.

• LRT tunnel waterproofing 'compromised,' transit commission hears

"The path of water helps to identify where the expected voids are," explained Richard Holder, the director of engineering in the city's transportation department.

Holderwasn't especially surprised such gaps exist, given thetunnel is large and 2.5 kilometres long.

In fact, he said tubes to allow for grouting had been in the walls anyway, foreseeing this kind of work would need to take place at some point because such leaks happen in tunnels.

4 trouble spots east of Rideau

Holder explained when the tunnel was dug several years ago, there was a rough excavation followed by a layer of sprayed concrete. A yellowplastic waterproof liner then went on top, followed by the concrete walls that riders see while travelling on the LRT.

The gaps are between the visibleconcrete wall of the tunnel and the waterproof liner behind it.

"I've been sitting here thinking about the void, an existential question I guess," said Kitchissippi Coun. Jeff Leiper, who had a string of queriesabout the tunnel work at Thursday's meeting.

"My biggest concern is we're going to be playing whack-a-mole with these for a period of months or longer as we try to ensure the tunnel is sealed," he said after hearing how the water might migrate elsewhere even after a space is filled.

The councillor was reassured, however, when the engineering director told him there are four spots being targeted in the problematic areaeast of Rideau station, which RTM hopes to deal with during planned annual maintenance over two weeks inJune.

There could also be leaks to the west, Holder added.

Holder also told Leiperthe tunnel being built for the Stage 2 extension along the Ottawa River and Byron Avenue uses a different construction method. Rather than being bored underground, it's a "cut and cover" tunnel.

BayCoun. Theresa Kavanagh also asked if the water behind the walls was connected to the longstandingodourat Rideau station.

The water leaking through the wall is groundwater and without odour, Holder told her. There's still no final determination for the persistent smell, but the citydoesn't believe it's sewage, Holder said.