Collapsed pipe to blame for sinkhole at downtown intersection, official says
A collapsed clay pipe in a 120-yearold sewer system caused the large sinkhole that forced the closing of a downtown Windsor intersection for several days.
“The catch basin leads are fairly old,” said Mark Winterton, the city's acting commissioner of infrastructure services. “The joints between them are susceptible to failure. Over time an old pipe will grow weak. Especially clay.”
Traffic started flowing again through the repaired intersection of University Avenue and Church Street on Thursday night, after the streets had been closed since last Monday.
After a stretch of heavy rain, the sinkhole suddenly opened up Monday when a catch basin lead underneath the road collapsed, according to the city. A catch basin lead is a pipe that connects the catch basin, a chamber that collects storm water and debris, to the main-line sewers.
In this case, the catch basin lead was a clay pipe. Winterton wasn't sure how old that pipe was, but he said the main line sewer it connected to was installed in 1905.
“You have pavement here that was fairly thick, and the catch basin lead failed, collapsed,” said Winterton. “Over time, soil and water go into the pipe and leave a cavern underneath the road surface.”
The cavern eventually grew so big that there was no support for the heavy asphalt on top, he said.
The city first sent out a detour notice last Monday night, warning that the intersection was closed. The road buckled up and caved in around 5:30 p.m.
The intersection at Church Street and University Avenue was shut down, and both streets were closed within a block's radius from the sinkhole in all four directions.
Winterton said crews replaced the pipe and filled the hole with non-shrink fill, a “super low strength concrete.”
“When they say super low strength, when it hardens you can actually shovel it,” said Winterton. “But it doesn't shrink. That allows us to get in there quickly.
“The other way we could have done it is backfilled granular. But that takes quite a bit of time. You have to compact it and make sure it's packed properly. This is a lot easier and faster.”
Workers then put the asphalt patch over the filler. But while investigating the underground terrain in the area, they actually found another pipe along Church Street that must also be fixed.
“We're going to have to go back in another week or two to do that repair,” said Winterton. “But we won't have to close down University for that.
“It's another pipe. It hasn't got to the point where it's collapsed.”