Owners of construction site ordered to investigate downtown sinkhole

The city has ordered the owners of a downtown construction site to pinpoint the cause of a large sinkhole that has led to the closure of part of Fourth Street S.W. since last Friday.

The City of Calgary issued an order Thursday requiring Pointe of View Developers to obtain a conclusive engineering report on the condition of the earth behind the shoring walls of the Gateway-Midtown condo project at 517 10th Ave. S.W.

Fourth Street between 10th and 11th Avenue has been closed sinceApril 24when the sinkhole a cavity in the earth that can be caused through erosion was first detected. The city said that section of the street will remain closed until further notice, but the sidewalk on the east side of the road will reopen by the weekend.

Preliminary investigation and engineering reports have helped the cityidentify the "nature of the sinkhole," a city news release said Thursday, but it's necessary for more complex work to be carried out in order to obtain a more accurate assessment.

The city has instructed the site owners to take the scaffolding and its temporary offices off the east side of the construction site and to remove the sidewalk. The work will allow a conclusive engineering report to be done which willidentify any other voids and propose a course of action.

City officials estimated Monday that the sinkhole is about six cubic metres in volume. The crater, about eight metres below street level, is believed to be directly underneath several lanes of traffic.

Previous report made 'urgent' recommendations

The sinkhole is right next to the twin-tower condo construction site that was abandoned by its original developer in August.Court documents obtained by CBC News show there have been concerns in the past about the stability of the seven-storey open pit.

Deloitte and Touche, who took over the project as a receiver, hired an engineering firm to examine the site. A report in December made several recommendations, with some of them described as "extremely urgent," including:

• Bracing the bottom of the excavation.
• Pumping waterout of the pit.
• Continuously monitoring the shoring up of the pit.

The cost to secure the site was estimated at $2.2 million. Ald. John Mar said Wednesday he doesn't know if any of that work was carried out, or if it played any role in the creation of the sinkhole.