Last week, a Calgary landlord strolling through her building’s parking lot discovered that the front tire of a pickup truck had inexplicably slipped beneath the asphalt and was dangling above a depression two metres deep. “The dirt just disappeared,” she told local radio. “They’re not even sure where all the earth went.” It was Calgary’s latest sinkhole.
Two weeks earlier, the city had evacuated a condo that officials feared was structurally compromised by another chasm that opened up under the earth; 13 residents found themselves homeless for days as a result. Earlier in the month a third sinkhole, associated with a financially troubled downtown condo project, had extended out onto city property to threaten a busy thoroughfare, forcing its closure for over a week.
Indeed, across downtown Calgary, idle or sluggish construction pits the size of inverted aircraft hangars risk upsetting the subterranean order of things. For the first time in over a decade, economic hard times have pushed the city to issue orders—16 of them—requiring that developers look after their stalled project sites. Last fall, officials identified 40 large pits, projects worth over $10 million each, as potential risks worthy of monitoring. That list has since been paired down to a dozen—six critical.
The difficulties all involve shoring—the latticework of beams built into excavations holding the earth at bay—that developers never imagined would be required beyond their 18- to 24-month lifespans. Twice, the city has sought resolution from the courts. “We were starting to see the potential for collapse of the banks,” says Kevin Griffiths, the city’s manager of building regulations, of one such pit. “We are anxious to see these things progress.”