SEFFNER — A huge sinkhole that opened under a house and killed a man in February collapsed several times while emergency crews responded to the scene, newly released documents show.
At one point a listening device placed in the hole to monitor sounds also was buried in a collapse.
These and other details were revealed in documents released Thursday by Hillsborough County officials.
"We have worked hard to bring as satisfactory a conclusion as possible to an incident that will long live on for the families involved," wrote Hillsborough County Administrator Michael S. Merrill.
The sinkhole opened about 11 p.m. Feb. 28 below Jeffrey Bush's bedroom on Faithway Drive.
When crews arrived, they discovered the sinkhole had swallowed an entire bedroom, where Jeffrey Bush had been sleeping in his bed. His body was never recovered.
Documents note that when Hillsborough County Fire Rescue's Urban Search and Rescue Team arrived, responders, including engineers from Bracken Engineering, lowered listening devices into the sinkhole.
A second collapse unfurled, burying one of the listening devices 30 feet below the surface, documents show. Workers watched the wire move from the back window of the house.
During the night, a third collapse took place, and emergency crews were then forced to leave the house. Geophysical specialists and other experts were called in to conduct soil sampling, records show.
"We knew that it wasn't done moving," said Drew Glasbrenner, senior geologist at Bracken. "We had to do some quick calculations, how far back we needed to stay."
The tests concluded that the sinkhole was about 15 feet wide and about 20 feet deep. A "disturbed area" of soil with a radius of about 50 feet from the hole also was discovered, documents show, which prompted officials to create a safe area extending 100 feet from the collapse.
Experts determined, documents show, that a "slightly cemented clay-sand" layer sat between 12 and 18 feet below the surface. Under that, varying between 20 and 25 feet from the surface, lies a second layer of soft clay, that, if disturbed, "may have started the sides to move again, causing a wider collapse," documents show.
And because the walls of the sinkhole were vertical, another collapse caused by settling soil "could happen at any time."
"It was determined that, unfortunately, a rescue or recovery mission could no longer be justified," Merrill wrote in his memo. "The instability of the hole and its depth regrettably led to the conclusion that the body could not safely be retrieved."
For the next few days, family members who once called 240 Faithway Drive home watched as crews demolished the house.
Workers dumped four truckloads of gravel to cover the hole.
Geologists at the scene also concluded the sinkhole was created through natural causes. (Click bit.ly/12YXUjZ to read the full report.)
"Fine grain sand eroded away during rain or other water events," Merrill wrote. A hole formed underground, expanding into the upper layer of the ground. But as the opening moved upward toward the surface, it widened and collapsed.
The structure also was discussed in the report, which notes that the welded wire fabric among the pieces of slab recovered by workers was corroded, allowing the slab to "fail and drop."
But, Glasbrenner said, "The state of the foundation has nothing to do with how big the hole was."
The documents were released the same week demolition began at 238 and 242 Faithway Drive, the two homes on either side of the house where the sinkhole formed.
Demolition costs were covered by the county. It was scheduled to be completed by today, said Hillsborough County spokesman Willie Puz.
The costs of the investigation were not available Thursday. Officials are now trying to determine the fate of the three properties and whether they will be transferred over to the county.
In his 15 years as a geologist, Glasbrenner said he has never seen someone die in a sinkhole.
"It's the most tragic," he said.
Laura C. Morel can be reached at firstname.lastname@example.org or (813) 226-3386.