A visible dip can be seen from a small, localized sinkhole on Victoria Rd. created by a mineshaft. (Ian Holmes/NanaimoNewsNOW)

By Ian Holmes

extended repair

Fixing Nanaimo sinkhole presents unique challenges

Mar 7, 2024 | 5:24 AM

NANAIMO — While the source of the problem isn’t surprising, addressing it is proving to be trickier than expected.

Discovered by a concerned resident in mid January, the City is working in coordination with on-site specialists to properly stabilize a sinkhole from a historic mine on Victoria Rd. near Rainer St.

Poul Rosen, director of Engineering for the City of Nanaimo, said video footage showed the open void is only five to six metres beneath the road’s surface.

“It’s very, very shallow here…it really makes for quite a vulnerable spot in the mine,” Rosen said.

Douglas Mine operated between 1860 and 1883, according to a Vancouver Island University research portal.

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With its entrance in downtown Nanaimo, the Victoria Rd. dip is located at the southern end of the mine, Rosen said.

Tunnels from the mine also extended beneath the Haliburton Rd. area.

As an early working operation, Rosen said the mine was not designed to collapse on its own after coal was extracted like later work sites were.

He said the localized sinkhole was created from falling debris which pushed the mine’s void upward toward the road’s surface.

“What ends up happening over time as that flaking continues and that bulking on the floor continues – the void will continue making its way up, up, up through the roof rock.”

A section of Victoria Rd. remains closed. (Ian Holmes/NanaimoNewsNOW)

Holes punched into the earth’s surface will allow infill to be injected into the void to stabilize the area in the weeks ahead, Rosen said.

The job has been further complicated and delayed, he said, by excess groundwater flowing into the void.

A plan to effectively stabilize the site is guided by video footage and ground penetrating radar.

“The grout and the concrete has to go in a few different layers because the mine void is on an angle, it’s actually on a 15 degree dip.”

Rosen is hopeful the second phase of the project can go ahead within about three weeks.

“Once that stabilization is complete, we can switch over to some more conventional construction and repair the utilities and restore the road.”

Victoria Rd. between Needham and Rainer streets remains closed for safety reasons, however local residents still have unobstructed access.

Rosen said the City has maps of the entire mineshaft inventory and occasionally address issues such as minor sinkholes as they arise.

“This particular area along Victoria Rd. is where we’ve had the most prolific coal mine related subsidence issues since ive been here since 2009.”

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Ian.holmes@pattisonmedia.com

On Twitter: @reporterholmes