Geosynthetics August/September 2021 - 24

Geosynthetic portable cofferdams for civil construction applications
Wash. This included removing the outdated
culverts and installing a new elevated
bridge, which replaced a causeway
as part of creating 2,300 acres (931 ha)
of productive fish habitat in the Puget
Sound region. The first phase of this
project included restoration of the channel
on the north side of the highway in
a sensitive marine environment. Figure
5 shows the cofferdams being deployed
during tide out conditions.
FIGURE 5 Kilisut cofferdams being deployed at low tide
Additional site-specific details and
risk assessment must also be predetermined
for each project.
This is done by completing a detailed
site assessment prior to installation.
Important criteria required for this assessment
includes the water body type (lake,
river, stream, ocean), anticipated water
depth, historical water depths, water flow
rates, freeboard level and ground surface
conditions. Site-specific project assessment
forms are required by the manufacturer
for each project estimate.
Case study:
Kilisut Harbor, Wash.
In 2019, the North Olympic Salmon
Coalition and the Washington State
Department of Transportation needed
to restore the historic tidal channels
and fish runs between southern Kilisut
Harbor and Oak Bay in Jefferson County,
24
Geosynthetics | August September 2021
Project scope
As part of the new bridge construction,
the project scope required the contractor
to excavate and dewater a large channel
in an environmentally sensitive region
for the protection of salmon stocks
and their migration. To address these
environmental concerns, silts and sedimentation
from construction had to be
tightly controlled. Based on the project
constraints, the engineer and contractor
chose a temporary portable cofferdam.
Layfield USA Corp.'s modular cofferdam
system was chosen for the project. The
project scope included the manufacturing
and installation support of 1,400 feet
(427 m) of multiple-sized dams of 4, 6,
8 and 12 feet (1.22, 1.83, 2.44 and 3.66
m) in height. The installation started in
September 2019 with a crew of seven
field technicians.
Project challenges
The project faced several unique challenges.
One of the main challenges was
working in tidal conditions that required
the installation of the dams to only take
place during low tide cycles. The contractor
was also not allowed to operate
equipment on most of the site in order
to protect the pickle grass and wetlands
area. This required many of the dams to
be unrolled and positioned manually.
With the multiple-sized dams, special
fabricated collars were manufactured to
connect the different sizes on-site.

Geosynthetics August/September 2021

Table of Contents for the Digital Edition of Geosynthetics August/September 2021

Geosynthetics August/September 2021 - Cover1
Geosynthetics August/September 2021 - Cover2
Geosynthetics August/September 2021 - 1
Geosynthetics August/September 2021 - 2
Geosynthetics August/September 2021 - 3
Geosynthetics August/September 2021 - 4
Geosynthetics August/September 2021 - 5
Geosynthetics August/September 2021 - 6
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Geosynthetics August/September 2021 - Cover3
Geosynthetics August/September 2021 - Cover4
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 1
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 2
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 3
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 4
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 5
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 6
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