Soil conditions vary across the bottom of the bay. Loose, fine sands comprise the upper layers, with medium to dense gray to green, clay-like fine sands in the lower layers. Geiger described the environment as extremely aggressive, with chlorides exceeding 18,000 parts-per-million (ppm).

“We went to a microsilica concrete, which is more corrosion-resistant, ” Geiger said. “The chlorides from the salt water won’t intrude as much on a microsilica-type concrete. It’s a denser concrete.” Pile groups vary from 12 piles to 22 per combined footing, with footings ranging in size from 1,200 to 1,400 cu. Yds. The ultimate bearing capacity will vary from 2,200 to 3,200 kips (kilopounds). Footings in the center channel have been designed to resist lateral ship impacts of up to 3,500 kips.

Those closer to shore have lower impact requirements.
For each pile, crews install a steel template, which serves as a guide for pile placement, then the pile is lowered into position and jetted.

A Manitowoc 4100W crane is mounted on a ringer pedestal on a 72-ft.-long, 250-ft.-wide, 5,400-ton-capacity barge called the Granite 1.
The crane is equipped with an additional 240-ft. boom from a Manitowoc 4600.

The crane lifts piles, the frame assembly and the hammer into place.
A Bruce model SGH 3013 hydraulic hammer, with a ram weight of 66,140 lbs., is used to drive the piles.
” The hydraulic pile hammer [is] 5 ft. across; a guy could stand inside the area where the piles are put in, called the helmet,” Geiger explained.
“When you think about the force [of] the 66,000-lb. ram times the 4-ft. drop, you’re talking about a potential energy of 225,000 lbs. of foot force.”

Piles are driven at a battered angle of 1 in. horizontal on 12 in. vertical to handle ship impacts. It takes between two and three hours to drive each pile.

“The equipment is bigger, on a larger scale [than on typical projects],” said Geiger, adding that the increased size adds to the pile-driving process.
“Setting up is time consuming with this big equipment.”
QORE Property Sciences of Montgomery, Ala., is conducting pile dynamic analysis (PDA) and monitoring installation.

While driving, gauges on the PDA predict the capacity of the pile based on a computer model with soil parameters.
PDA testing is done on a test pile in each foundation. With stronger soils, shorter piles can be used.

Applied Foundation Testing Inc., Green Cove Springs, is performing statnamic testing, which replaces standard load testing.
At presstime, the company had completed four 30-meganewton axial statnamic tests and two four-meganewton lateral statnamic tests at various locations across the bridge.

“It’s like a small rocket,” said Geiger of the device used to perform this testing.
“You set it on there with rocket fuel. It weighs a certain amount.
You ignite the fuel, and get thrust, which as you are lifting this mass, it is pushing down on the pile. You have internal gauges in the pile and you can tell the stresses, strains and capacities you have in the pile.”

The westbound, northernmost bridge will be completed first and opened to two-way traffic.