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Sunday, Nov 23, 2014
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Experts debate reinforcement options for deadly Seffner sinkhole

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TAMPA -

The small, bright blue house in Seffner had load-bearing reinforcements in its windows and a wire mesh matrix embedded in its concrete foundation, county officials said.

But the structural design was not strong enough to withstand a sinkhole opening under a bedroom, swallowing 37-year-old Jeffrey Bush as he slept. The story drew worldwide attention as Bush was presumed dead and authorities decided it was too dangerous to recover the body.

The house at 240 Faithway Drive was built in 1974, but sinkhole repair experts say no building, even ones constructed under modern guidelines and boasting the latest reinforcement technology, can escape damage if the ground under them subsides or completely caves in.

“Sinkholes are going to cause damage no matter what you do,” said Rodger Bennett, owner of RAB Foundation Repair in Odessa.

The only option homeowners have is to minimize damage — and that option is expensive.

The cost to reinforce homes ranges from $20,000 to $100,000 because workers have to drill down past the limestone to solid bedrock to install steel piers or inject concrete grout, said Jaime Wester, owner of Champion Foundation Repair in Tampa.

“The price depends if the limestone is 20 feet underground or 100 feet,” Wester said.

Hillsborough County building codes do not require new or existing homeowners to have these features on their property, Wester said.

But the high prices prompt most homeowners to pass on these specialized reinforcements, she said.

Bennett said there are three common techniques his company uses.

“The only thing that can repair a sinkhole is compaction grouting,” he said, referring to the process of filling in the cavity with concrete grout and gravel. “But that can’t guarantee the foundation will be stabilized.”

Stabilizing the concrete slabs that sit under almost all homes requires underpinning, a procedure where steel piers — which look like giant screws — are driven into the ground to support the structure.

“If you take all the dirt away, it’ll look like the house is on stilts,” Bennett said. But if a stricken homeowner chooses only underpinning, “that process doesn’t fix the sinkhole.”

The third step is chemical grouting, which stabilizes loose soils on the surface.

If all three methods are required, the total cost is at least $200,000, Bennett said.

The home at 240 Faithway Drive, where Leland Wicker had lived nearly 40 years, had none of those features, county officials said.

The sinkhole opened in the east bedroom about 11 p.m. Feb. 28, pulling Bush, his mattress, dresser and television set underground.

The home was torn down on Monday.

Engineers found that the concrete foundation contained welded wire mesh, not steel rebar, which is thicker and stronger, county spokesman Willie Puz said.

The house also had lintels in its windows, structural supports designed to bear weight, Puz said.

An engineer who examined the site last week said the concrete slab was thin, which could have contributed to how badly the house was damaged by the sinkhole.

Ross McGillivray of Ardaman and Associates said a “more robust structure, modern design, may have survived better.”

Jerry Sanchez, a retired construction manager, said he watched news reports about the sinkhole with interest.

Sanchez said the house could have survived the sinkhole if steel rebar had been used in the foundation.

“If that house had rebar going each way, it wouldn’t have gone down,” Sanchez, 74, said.

But installing rebar is not common practice in residential construction.

“It’s not normal,” Sanchez said. “It’s just not done. It’s too expensive.”

Wire mesh is typical, he said.

“It’s supposed to prevent cracks,” Sanchez said. “But concrete is concrete. It’s going to crack.”

Bennett, the sinkhole repair expert, said there’s really no engineering or construction feat that could prevent sinkholes or the damage they do.

“You can only do so much,” he said. “And to actually stop the cause of a sinkhole? That’s really not going to happen.”


rreyes@tampatrib.com

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