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The city’s engineering department recently completed a formal study of pavement failures after too many new concrete streets have buckled, particularly in the southern part of the city, as seen Thursday at Sundown Boulevard and Mustang Drive in Denton.

Denton’s engineering department is keeping a close watch on more than a dozen new subdivisions, most in the city’s fast-growing southern sector, where concrete streets are failing at a troubling rate.

Denton City Engineer Todd Estes briefed the City Council earlier this month on new findings, and the city has spent about $5 million so far repairing nearly 7 miles of new concrete streets that were supposed to last 20-30 years.

“Some may need to be fully reconstructed,” Estes told council members during a work session on March 5, adding the city will need to spend $1 million to $2 million annually to keep up with the failures for now.

Estes told city officials a year ago the concrete street failures needed closer scrutiny if the city was to solve the problem for the long term.

In many cases, Estes said, there wasn’t a problem with the concrete itself but how the street was built. The failing streets were all built by private developers and their contractors. The city had specifications for the work and inspectors who were supposed to verify the roads were built as required. The city also required the roads come with a two-year warranty.

To better understand what was happening, the city hired an outside engineering firm to sample all the failing roads and make recommendations. The company took 71 samples in 61 locations to figure out what happened and come up with a plan.

Most of the failures could be attributed to one of three things: One, a popular construction technique failed to fully compact the soil around the underground sewer lines. Two, panels were spaced without room to expand and contract in the extremes of Texas weather. Three, some streets failed because of heaving — the specially compacted soil underneath the concrete moved.

The city’s engineering department beefed up both its requirements and its inspections to make sure the soils underneath new streets are being compacted properly. They also may ban the popular construction technique that contributed to so many failures, Estes said.

None of the requirements are unusual, he added.

“They are used across the nation to prevent failures,” Estes said.

Council members can expect to see a supplemental budget request later this spring related to failed concrete streets. Estes said his staff was continuing to work on a full inventory of failed streets to better get a handle on the future costs.

At the end of the briefing, City Manager Todd Hileman set aside a rumor that other new streets were failing — the ones being built by city crews.

The city’s bond oversight committee was concerned about streets being rebuilt with 2012 or 2014 general obligation bonds.

Both Hileman and Estes said those streets were built to the newer, tougher standards and were performing well.

PEGGY HEINKEL-WOLFE can be reached at 940-566-6881 and via Twitter at @phwolfeDRC.

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