|About Us | Gallery Search | About this Site | About Heavy Construction|
|Home > The Builders >|
Construction Close-Up: Boxes, Bases and Towers Foundation Work Picks Up
Out on the Bay, work on the Skyway foundation is accelerating as construction crews position key substructure components in preparation for the driving of support piles.
Crews have begun placing steel footing boxes inside the de-watered cofferdams just west of the Oakland shore. These boxes will form the base of the Skyway's 28 foundation piers. Workers have also begun positioning the giant pile driving templates that will guide 8-foot-diameter tubular piles as they are driven, or battered, at an angle deep into the Bay mud to provide support for the Skyway's piers and, ultimately, its roadway.
The piles will be driven with a "hammer" suspended from the General Construction company derrick barge, The General, one of the largest such cranes on the West Coast. (photo of hammer here).
As they are driven through the templates, each pile will be welded to another to form one long single pile of two sections. The total length will vary according to location, but an average length will about 300 feet. Crews will then clean out the piles, insert a rebar cage into each and fill them with concrete.
The pile driving templates are engineering marvels unto themselves. Massive and intricate steel beam and tube structures, the template bases and towers together weigh nearly 400 tons and host a system of hydraulic gates that can be adjusted for the number and angle of the piles to be driven by the crew of eight or more craftworkers and supervisors.
On Jan. 29, crews lifted the first 220-ton pile driving template base and positioned it inside the dewatered Pier 16 cofferdam just off the Oakland shore. The base, 63 feet wide and 25 feet tall, was deftly set atop a footing box that was made in Corpus Christi, Texas, and shipped to the site on barges. Before the boxes are set into the cofferdams, they are partially filled with concrete to a depth of 1.5 meters. They are then lifted and set in place by a catamaran capable of lifting 2,000 tons.
The next day, crews installed the tower section onto the base, delicately positioning the mammoth structure onto spud piles stabbed into the base. The 75-foot tower rises above the road deck of the existing bridge, a stunning reminder that work is progressing below the water line.
In coming weeks, pile driving templates will be installed at two more eastbound pier locations. From then on, three pile-driving templates will be in action on the Bay at any given time. Whenever all the piles are driven at a pier location, the template will be dismantled and moved to the next pier site. Each footing box will then be filled with an average of 1350 cubic yards of concrete in two separate pours.
In all, each foundation and pier column will take about nine months from start to finish.