POWER October 2010 - 74

PLANT CONSTRUCTION
Deep Excavation Support Systems
Speed Plant Construction
As part of constructing the recently commissioned We Energies' Oak Creek
Power Plant Elm Road units, four remarkable below-ground structures
were built. Each unique structure required creative designs and meticulous
construction techniques to meet the project's distinctive requirements.
By K.R. Bell, PhD, PE and J.R. Davie, PhD, PE, Bechtel Power Corp.
B
echtel Power Corp. (Bechtel) is currently
completing a contract to engineer,
procure material for, and construct
(EPC) the We Energies' 1,135-MW
Oak Creek Power Plant Expansion Project
(OCPP, also known as the Elm Road Generating
Station). Construction started in 2005
on the two-unit plant located on Wisconsin's
western shore of Lake Michigan. OCPP is an
expansion of the existing Oak Creek coalfueled
power plant. For this achievement,
POWER recognizes OCPP as a 2010 coalfired
Top Plant. A companion article (p. 44)
provides more project-specific details.
One of the unique challenges encountered
by Bechtel on this project was the construction
of several complex below-ground structures. In
this article, we describe four of these structures
and discuss why a particular earth retention
system was selected for each. We believe that
there were lessons we learned during the design
and construction of this project that will be useful
to others involved in similar projects.
Four Structures, Four Solutions
OCPP required construction of a series of three
deep excavations related to the water supply
system and one excavation related to the delivery
of coal to the plant. Each project required
unique engineering and construction approaches,
especially where the selection of the earth
retention support systems was concerned. As
always, economic and schedule considerations
played a significant role in the final selection.
The four structures discussed are:
■ A series of three vertical shafts was constructed
for a rock tunnel that extended
out approximately 2.7 kilometers (km)
under Lake Michigan. Each shaft was
constructed by building and sinking a precast
concrete section to the top of rock at
a depth of about 30 m. Two of the three
shafts were constructed on land, while the
third was constructed over water.
■ An intake water pump house was constructed
using slurry wall techniques to
74
1. Creative caisson installation. This caisson was designed to extend compressed
air, water, and power lines down to the bottom for construction workers. The caisson was built
at ground level and then workers dug out underneath and let gravity sink it into the ground.
This process was repeated two more times, until the bottom caisson literally hit rock bottom.
Courtesy: Bechtel Power Corp.
a depth of approximately 20 m with multiple
levels of tie-back anchors.
■ A multiple-layered braced sheet pile system
was used to construct a gate structure
in Lake Michigan as part of the intake water
scheme to shut off water flow to the
existing plant intake structure.
■ A rotary railroad car unloader was installed
that incorporated the use of two
soldier pile and lagging walls, the upper
wall having a single level of tiebacks while
the lower wall had multiple tieback levels.
The total depth of this structure was also
about 20 m. The upper wall was added
during construction to protect an operating
rail line that was jeopardized by the
originally planned open excavation.
All the structures were successfully completed
and are now in operation.
www.powermag.com
Tunnel Shaft Construction
POWER reviewed the design aspects of
OCCP's upgraded cooling water system in
" Oak Creek Power Plant Upgrades Cooling
Water System, " March 2009 (available from
POWER's online archives at www.powermag
.com). In summary, We Energies elected to
upgrade the circulating water system for the
entire plant to comply with Section 316(b) of
the Clean Water Act by constructing a new
common system to serve the four existing
units plus the two new 615-MW OCCP units.
However, not discussed in that article were
the engineering and construction challenges
of drilling a new 8.25-m-diameter intake
tunnel system that projects approximately
2.4 km offshore to collect cold water from
near the bottom of Lake Michigan. This new
structure replaced both the existing shoreline
intake and supply water for the new plant.
POWER | October 2010

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POWER October 2010

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