Chicago: Heavy load from unknown source said cause of major water-main rupturegreenspun.com : LUSENET : Grassroots Information Coordination Center (GICC) : One Thread
Heavy load caused water-main rupture
April 6, 2000
BY ROBERT C. HERGUTH STAFF REPORTER
A sudden heavy load on the pavement at Quincy and Wells was to blame for the massive water main break Feb. 7, according to findings released Wednesday.
It could have been a large passing truck, officials said, but they can't be sure what it was.
The rupture, which snarled downtown traffic and L service for days, was not caused by water pressure, corrosion, a water leak or a material defect, Chicago Water Commissioner Richard A. Rice said.
A city-commissioned analysis, conducted by the Northbrook-based engineering consulting firm of Wiss Janney Elstner Associates Inc., found that something applied between 17,000 and 30,000 pounds of pressure to the surface of the road. That force was then transferred to a 16-inch gas line about 2 feet below the pavement and through the city's underlying electric duct bank to the 36-inch main.
There was a "concentrated force" of at least 16,000 pounds applied to the top of the main, which was about 100 years old and had inch-thick cast iron walls.
The main sustained a wedge-shaped crack 62.5 inches long, Rice said. It has been replaced.
So what caused the initial pressure?
"Therein lies the question," Rice said. "Did two cement trucks pass at the same time? The axle of one of those trucks can be 30,000 pounds. . . . It was probably a vehicle of some kind that had that kind of weight. But you can only speculate."
Downtown construction wasn't believed to be a factor, he said.
Rice said it wasn't clear whether the weight of a vehicle caused the initial pressure or whether wheels bounced onto the roadway after hitting a pothole or bump.
Preventing similar breaks in the future will be difficult, Rice said. But city officials have decided to inspect underground utility lines whenever Loop construction requires digging, he said.
The investigation isn't over, and there could be more findings.
-- Carl Jenkins (Somewherepress@aol.com), April 06, 2000