PUBLIC WORKS/Sarasota’s sinkhole solution: polyethylene pipe
Like alligators and high humidity, sinkholes are a fact of life in Florida. And last summer, the sinkholes that plagued Ravena Street in the city of Venice proved especially challenging for the Sarasota County workers who tackled the job of repairing them.
The crux of the problem was a failed 30-year-old metal storm sewer that ran within four feet of a home and was buried about 10 feet deep, says Gary Downing, project engineer for the Sarasota County Department of Transportation. Compounding matters, workers only had about 35 feet of space between the house and a neighbor’s swimming pool.
“We couldn’t safely dig out the existing pipe that close to the house,” says Roy Lessig, Sarasota County crew leader, “so the metal pipe had to be abandoned and filled with concrete, and the new pipe had to be offset around the old system.”
Sliplining was deemed not feasible because the existing pipe was too deteriorated. So Sarasota County chose to replace the pipe, using 60-inch Sure-Lok HDPE pipe manufactured by Hancor, Inc., Findlay, Ohio.
The pipe is supplied in 20-foot lengths weighing about 900 pounds apiece. “They were able to pick it up and move it around just using a small backhoe,” says Downing. By contrast, concrete pipe, which weighs nearly 11,000 pounds per eight-foot section, would have required a heavy duty crane for which there was no room, says Downing.
The pipe can also be deflected two degrees at each joint to allow for gradual deviation away from a straight line without junction boxes.
From the front yard, workers offset the new pipe 11 feet center-to-center from the existing line. They cleared the old metal structure and met the alignment of the existing system back beyond the house.
The county was able to forego a standard conflict box to accommodate a gravity-fed sanitary sewer line bisecting the stormwater pipe. Instead, the 12-inch sanitary sewer line crosses directly through the pipe two feet below its crest.
Downing estimates the total project cost $50,000 to $70,000 less than if other methods had been used and was completed about three weeks faster.
All told, workers took about six weeks to lay 450 feet of the pipe in a three-block area.