Bath-Woolwich Bridge, ME
deep footing block with the top of the
footing about three ft below low tide.
This design is very efficient because it
significantly reduces the depth at
which the footing is constructed. How-
ever, it does create the problem of how
to construct an underwater footing
suspended 28 ft off the river bottom.
In order to address this problem and
reduce the amount of work in the river,
Ben C. Gerwick, Inc. proposed the fol-
lowing construction sequence:
• Pre-install the drilled shafts using a
Mating of follower cofferdam to floating precast footing shell. two stage template.
• Construct a precast footing shell on
Constructing bridge foundations under shore and attach a temporary steel
water is an expensive operation and follower cofferdam.
• Detailed Design
usually represents 40-50% of the total • Launch the cofferdam and tow it to
bridge cost. One way of reducing this • Constructability Studies the bridge site.
cost is to perform as much of the • Precast Shells (Hulls) • Position the cofferdam over the
foundation work as possible on shore • Tremie Concrete drilled shafts and fix it in position with
by prefabrication and then floating (or • Casting Yards/Launch System four spud piles.
lifting) completed elements into posi- • Cofferdams and Caissons
• Lower the cofferdam down over the
tion. With this objective in mind, Ben pre-installed drilled shafts with jacks
• Installation of Large-Diameter
C. Gerwick, Inc. teamed with Flatiron located on top of the spud piles.
Structures Company of Longmont, • Lock the footing to the drilled shafts
• Offsite Prefabrication
Colorado to design a floating coffer- by placing a four ft deep tremie seal.
• Positioning Control Systems
dam system for the Bath-Woolwich • Dewater the cofferdam and construct
Bridge across the Kennebec River at • Construction Engineering the footing and pier shaft in the dry.
Bath, Maine. • Flood and remove the follower
cofferdam for reuse on the next pier.
The Maine DOT awarded the design-
construct contract for the 3,000 ft long This construction sequence minimized
four-lane bridge to Flatiron and Figg work in the river and allowed the drilled
Engineers in August of 1997, and shaft installation to proceed concur-
shortly there after Ben C. Gerwick, Inc. rently with the onshore fabrication and
was contacted by Flatiron to design a launch of the cofferdams.
Ben C. Gerwick, Inc. 01-027e-02a
safe and economical cofferdam system
for the six main river piers. Figg’s de-
Year of Completion: 2000
sign for the piers was based on using
eight ft diameter drilled shafts. A typical Construction Cost: $35M
pier foundation is located in 45 ft of Client: MAINE DOT,
water and contains four drilled shafts Flatiron Structures Company LLC
supporting a 33 ft by 36 ft by 12 ft