PROJECT SPOTLIGHT
By Rodney Gordon, Balfour Beatty Infrastructure Inc.
Balfour Beatty Infrastructure Inc.
(BBII) is currently constructing
the Woodland-Davis Clean Water
Agency Joint Intake and Fish Screen Project
on the west levee of the Sacramento
River just west of the Sacramento International
Airport. This $45 million project,
scheduled for delivery in February 2017,
will service both the cities of Woodland and
Davis for surface drinking water, and Reclamation
District 2035 providing 320cfs of
irrigation water for their agricultural operations.
Three each cofferdams were required
to construct this project; one to facilitate
construction of a water discharge structure
into an adjacent canal, another to facilitate
demolition of the existing pump station that
the new pump station will be replacing and,
most significantly, a cofferdam to facilitate
construction of the new, 3,850-horse-power
intake pump station.
Construction on the new intake pump
station cofferdam started in June 2014; the
last sheets were driven in August of that
same year. This cofferdam was built in
the side of the levee and extended out into
the Sacramento River and because of this
orientation there were large loads imposed
on the cofferdam by the levee. In order to
support the large loads from the levee, sections
of the levee were excavated down to
minimize the load on the cofferdam. Next,
combination walls consisting of 54 each of
60 and 70-foot long, 36-inch diameter pipe
pile and 84 pairs of 60-foot long PZC-26
sheet piles were selected by BBII to achieve
a large enough section modulus to support
the remaining loads imposed by the levee.
The cofferdam combi-wall installation was
conducted primarily with a Manitowoc 999
crane using an ICE® 66 vibro hammer, and
APE D-30 and D-36 impact hammers were
used where harder driving was encountered.
Internal bracing of this cofferdam consisted
of two levels of 36-inch I-beam walers, and
eight 36-inch diameter pipe struts.
Once the coffer cell sheets, pipe pile
and bracing were in place, 9,000cy were
then excavated from inside the cofferdam to
approximately 30 feet below river elevation
using a long-reach Cat 385 excavator and
a clam bucket on a Manitowoc 999 crane.
Following excavation, 357 eighteen-inch
diameter structural pile – ranging in length
from 45 to 60 feet – were driven to a top
elevation approximately 10 feet below the
water surface using an APE D-19 hydraulic
impact hammer. Following installation of
the structural pipe pile, an eight-foot thick,
3,800cy tremie slab was placed underwater,
sealing off the cofferdam. The cofferdam
was then dewatered and construction of the
new intake pump station was able to begin.
In order to access the intake pump
station cofferdam for construction of the
cofferdam and concrete structure, BBII
constructed a 32-foot-wide by 175-foot-long
trestle, consisting of sixteen 36-inch diameter
pipe piles driven to a service capacity
of 240 tons, 36-inch stringer and cap beams
and a timber crane mat deck. This trestle
was rated to support a 275-ton crane at full
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