Huntington Beach, in Orange County, Southern California, is known throughout the world as "Surf City, USA." Within a short walking distance from the beach front and its famous pier, a 34-acre mixed-use development is under construction. But early pile construction hit a few snags.
The original design for the foundations of underground parking and other structures at the new site was based on the use of piles driven into the underlying dense sands.
"Some pre-cast concrete piles had been driven to refusal, but noise and vibration levels caused concern because the construction area is surrounded by homes and a nearby hotel," said Dale Scheffler, president of D.J. Scheffler, a drilling contractor based in Pomona, California.
"Being so close to the ocean, also there's a very high water table and a dense sand layer at 40 feet that made driving the precast piles difficult," he said. So, the developer, Makar Properties, asked the company to evaluate alternate foundation systems.
Michael Zeman, also of D.J. Scheffler, evaluated the load requirements of the foundation system and geotechnical conditions on site. He figured a CFA pile system could meet the required capacity, while maintaining schedule and reducing vibration concerns. Scheffler submitted a proposal and suggested a test program.
CFA piling systems use a continuous hollow stem auger that places pressurized concrete into the shaft as the auger is withdrawn. This is similar to auger cast piling, but CFA uses both high-strength concrete and full-length rebar cages rather than top cages, center bars and grout.
"These differences are significant," Zeman says. "They increase the load capacity of the piles and allow them to be used in areas with high lateral loads." An onboard computer in the drill rig's cab measures depth, rotation and concrete placement to keep the piles within specs, he added.
Scheffler has already installed and tested 24-inch-diameter piles to a depth of 55 feet at the Pacific City site. "The first test results were very positive, exceeding our capacity expectations by 10 percent," says Zeman. "We are now installing three, 30-inch diameter test piles as a second test. These will receive a compression load of approximately 1,500 kips. This is an extremely high test load, much higher than would be used for a driven pile foundation system."
Zeman said these high-compression loads are achievable through conventionally drilled CIDH piles, but they are typically very costly, particularly in soft soils with high groundwater. Costs would include the need for casing and slurry.
"We have been pleased to verify through the load testing that the CFA piles not only easily exceeded the capacity of a driven pile, but also exceed the estimated load capacity of the more expensive CIDH piles," he added. Once the go-ahead is given, the CFA piling quantity will be somewhere between 600 and 900, depending on the number of 30-inch piles used, he said.
Although Sheffler's company can use any method of drilling, he is especially mindful of CFA's safety factor.
"Every year, throughout the U.S., there is a worker in our industry lost to a cave-in of a drilled shaft during construction of CIDH pile," he said. "CFA piling significantly reduces these risks by immediately replacing soil with concrete during extraction of the auger — a much safer method since there is never an open shaft."