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One-Inch Clearance
Is No Problem In Power Plant Renovation
How do you quickly remove 1.5 million pounds of heavily reinforced
concrete located 35 feet above grade, inside an operational
power plant, with 1 inch of clearance on four sides? While
you're at it, make sure you don't disturb the surrounding
steam-turbine generators or interrupt daily production of
power.
These were the basic requirements
established recently by a Michigan utility company when planning
a turbine-generator replacement at a major coal-fired generating
plant.
The original 100,000 KW unit was installed
in 1944 and operated continuously, except for scheduled maintenance,
for the past 54 years. Recently, however, a nearby auto plant
created an increased demand for steam, which is a by-product
of the generating process. This demand warranted the replacement
of the old unit in favor of a more efficient and physically
smaller version. Unfortunately, the new unit would not fit
the old foundation and necessitated the removal and replacement
of the top 8' of concrete.
During the planning and design phase
of the project, the consulting engineer brought in Concrete
Cutting & Breaking Inc. - Grand Rapids - to help determine
the most cost effective and safe method of concrete removal.
Breaking and splitting options were deemed impractical due
to the following considerations:
- Vibration and dust caused by breaking
could damage the surrounding machinery and controls.
- Micro cracking of the concrete
caused by breakers was unacceptable in a foundation that
was expected to last another 54 years.
- Potential damage caused by falling
debris would create a risk both to surrounding pipes and
equipment (some as close as 6 inches), as well as to workers
35 feet below.
- Debris clean-up costs would be
prohibitively expensive and time consuming.
Diamond blade sawing and crushing
methods were also dismissed due to the 8' cutting depths required
to segment the 85' x 28' monolith.
At the consulting engineers' request,
CCB submitted a diamond wire sawing budget, schedule, and
schematic for evaluation. Rigging and removal chores were
to be handled by the owner's work force using a 200-ton over-head
bridge crane. Large pieces were to be cut free, lifted to
a modified 12 axle rail car, brought outside, and off-loaded
with a 500 ton rental crane.
CCB laid the proposed cuts out in
such a way that all the concrete could be continuously cut,
shimmed, and left in place prior to the arrival of the rigging
crew and equipment. Upon completion, the cutting crew would
vacate the site and allow the owner's crew to remove the pieces
quickly and safely in one continuous operation. This procedure
would minimize the expense of the rental crane, optimize the
rigging crew's time, and eliminate the hazard of having the
cutters and riggers working in the same place at the same
time.
The entire top 8' of the foundation
was sectioned into seven pieces weighing up to 130 tons each.
In addition there were three smaller pieces that were cut
ranging from 4 to 43 tons. Reinforced steel was heavy and
the typical 8' x 8' vertical cut contained 106 1-3/8"
rods. In addition to the rebar there were also two heavy-flange
24' I-beams embedded in the structure. CCB completed nearly
1,200 square feet of cutting in eleven shifts by utilizing
multiple wire saws.
Once the 26' x 8' pieces were cut
free, they were ready for removal. To accomplish this lifting
maneuver, four 2-1/4" thick steel lugplates were strategically
located on each piece for easy removal. Each of the plates
were secured by four 1-1/2" diameter rods which were
epoxy glued into 1-5/8" x 18" deep holes. The final
balancing adjustments were made via 6-foot long turnbuckles.
This procedure allowed rigging crews to remove two pieces
per shift from the foundation.
CCB was again employed to vertically
core drill 215 4" diameter holes 2" deep around
the rebar. These holes were made so that a new rod could be
welded into place. This project was a good example of how
planning can result in a win-win situation for everyone. All
the demolition was performed just 20 feet from a control room
and 30 feet from a $15 million dollar turbine-generator, without
interrupting the everyday operations.
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