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FLOAT-IN
DAM - "In the Wet" Construction Methods
The Need
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"In-the-Wet" construction methods use
off-site prefabrication combined with lift-in or float-in of large precast segments onto
pre-installed foundations. The segments are locked onto the foundations by underbase
grouting and infilling of the segments with tremie concrete. These methods have included
the innovative use of large precast units, floating structures and cofferdams, large barge
crane installation, and deep foundation structures. "In-the-Wet" method would
offer significant advantages over the traditional fixed cofferdam method, including
substantial cost savings, shorter construction duration, reduced environmental impact, and
greater construction safety. |
The Technology
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Ben C. Gerwick, Inc. is teamed with Bergmann
Associates of Rochester, New York, and D'Appolonia of Pittsburgh, Pennsylvania, to design
a replacement for Dam 2 on the Monongahela River for the US Army Corps of Engineers.
Braddock Dam, on the Monongahela River, has been designed to be built using float-in
concrete shells, up to 333 ft. long, fabricated offsite, floated into place over
pre-installed foundation caissons, set-down, grouted in-place, then infilled with
concrete. |
Dam landing pre-installed caissons |
| The new dam will be a 600-foot long
structure with four gate bays. The "In-the-Wet" construction plan calls for
breaking the dam into two segments of 333-foot and 265-foot. The segments will be
constructed as closed bottom boxes in a two level casting basin. The bottom of the boxes
will be recessed for the pre-installed foundation caissons. As each segment is completed,
it will be launched by flooding the basin and towed to the site for final outfitting. It
will then be positioned over the foundation caissons with a mooring system mounted on the
segment. Each segment will then be ballasted down onto 6 landing caissons and leveled with
flat jacks. The pile tops and underbase will be grouted, and 8-foot of tremie concrete
will be placed in the segment. Each segment will then be dewatered and the remainder of
the dam including tainter gates will be completed in the dry. This "In-the-Wet"
technology is expected to save $5 - $15 mil and reduce the construction time by one year.
The final plans and specifications were completed in October of 1998. Construction is
scheduled to be completed in 2002. |
 
Completed dam in
operation
View of heavy lift crane moving precast element |
The Benefits
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This method offers several advantages over
conventional "In-the-Dry" construction:
- Lower construction cost by
transferring a significant amount of the work from out in the river to on land
construction.
- Lower construction risk by
transferring from a marine environment (subject to flooding and other risks) to an onshore
precast facility.
- Shorter construction time by
allowing the use of concurrent construction of foundations and fabrication of the
precast shell.
- Less disruption to existing
and on-going navigation operations at the site.
- Less environmental impact by
transferring most of the work out of the river and on to shore where any potential
environmental hazards can be contained.
- Less
effect on river flow. (This can be critical during periods of high flow.)
- Higher quality through the
use of precasting in a more controlled environment.
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Status
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Ben C. Gerwick, Inc. is taking the lead in
designing of the precast dam segments and developing the construction methods and
procedures for:
- Casting and launching of the pre-cast dam segments,
- Transport, positioning and immersion of the segments on to the
pre-installed foundations,
- Underbase grouting and tremie in-fill of the segments.
Gerwick has participated in numerous studies regarding the
use of off-site prefabrication technology for inland waterways for the U.S. Army Corps of
Engineers, including:
- Widening of Lock 4 on the Monogahela River for the Pittsburgh
District
- Increasing lock capacity on the Ohio River Main Stem for the
Louisville District
- Increasing lock capacity on the Upper Mississippi River for
the St. Louis, St. Paul, and Rock Island Districts
- A new lock for Inner Harbor Navigation Canal, for the New
Orleans District
- Numerous studies for the Waterways Experiment Station
regarding such topics as heavy-lift equipment, tremie concrete technology, and precast
concrete
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Barriers
Points of Contact
- Mr. Bob Bittner, Ben C. Gerwick, Inc. 601 Montgomery St.,
Suite 400, San Francisco, CA 94111, Tel:(415) 398-8972, Fax: (415) 433-8189, E-mail: RBB@gerwick.com
- Mr. Larry Edington, International Union Of Engineers (IUOE),
1125 7th St., NW, Washington D.C., 20006, E-mail: edgington@iuoe.org
References
- Ben C. Gerwick, Inc. <http://www.gerwick.com>
- U.S. Army Corps of Engineering, Pittsburgh District - Lower
Mon Project Factsheet
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
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