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Construction Status

CTH E, Oconomowoc River Structure, Waukesha County

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Project Snapshot

Construction is full speed ahead at the Monches Dam!
 
In the previous Construction Update Letter, the “CTH E – Oconomowoc River Structure and Approaches Project” at the Monches Dam was only in the early stages of construction. Radtke Contractors had just completed and opened a temporary diversion channel just north of the dam. The diversion channel was constructed to direct the Oconomowoc River flow around the existing dam in order to construct a new dam.  The diversion channel work began in the first week of February and the river flow was successfully diverted around the old structure in the first week of March. 

Since the river was diverted, there has been quite a bit of activity despite the continued rain, cold and snowy conditions that were endured in February.  Radtke has installed another cofferdam.  The first cofferdam they installed formed the containment for the diversion channel and this new cofferdam forms the containment around the dam structure.  Between the two cofferdams, Radtke has installed an estimated 11,000 square feet of sheet piling. Each sheet pile measures 1.5 feet wide by 25 feet tall; therefore, approximately 300 individual sheet pilings were installed in order to form the two cofferdams.  Oh, by the way, did I mention that all the sheet piling was temporary?  All 300 sheets will eventually need to be pulled out, cleaned, stacked, loaded on trucks and hauled away.

Within the sheets of the new cofferdam (around the dam), Radtke has dredged additional silts from the river.   All together, including earlier dredging that was done in front of the temporary diversion channel, Radtke has removed approximately 1,800 cubic yards of silts out of the river--that’s about 150 dump truck loads!  All this silt has been removed in an effort to minimize the transportation of silts downstream which could have negative effects on the downstream eco-system and recreation.

After the silt was dredged from the river bottom, Radtke placed a protective layer of heavy and jagged rocks, called “rip rap” on the river bottom.  This protective layer of rip rap is used to prevent the river bottom from scouring away and to help hold the remaining silts in place.  This rip rap is also being used extensively in the temporary diversion channel so that the sometimes heavy river flow does not eat away at the bottom of the temporary channel.  Radtke has placed more than 600 cubic yards of rip rap in the temporary channel and in front of the dam, which is approximately 800 tons of heavy rocks.

With the river dredged and the rip rap in place, Radtke started the demolition of the old bridge/dam structure. With the use of a modest back-hoe, the old dam came down pretty easily.  It only took Radtke two days to entirely demolish and remove the old structure. The rubble was loaded out into dump trucks and the way was cleared for laying the foundation of the newer and bigger Monches Dam.

The new dam, including its apron, will be almost three times as long (front of dam to apron) as the old dam at 85 feet long.  The new dam will be 27 feet wide and 8 feet deep.  Radtke began to work on the foundation slab of the dam on March 27.  The slab is 3 feet thick at the front of the structure and is founded on a 15-foot deep seepage sheet pile wall.  Radtke graded the stone base, set the forms and placed the rebar for the slab in six days and then poured the slab on April 4. 

Meet Our Team


If you have not already met them, our team includes:

Jim Clements, R.A. Smith National, Consultant Project Engineer

Brian Much, Radtke Contractors, Contractor’s Project Manager

Jim Ferg, Radtke Contractors, Contractor’s Project Foreman

Kevin Yanny, P.E., Waukesha County Dept. of Public Works, County Project Manager

Looking Ahead


Now that the foundation slab is poured, Radtke will start to form the two exterior walls and the middle wall of the dam.  The dam is actually a “double-barreled” box culvert with two sets of adjustable gates, one gate for each “barrel” or chamber.  The gates will be installed at the upstream side of the structure and will be used to control the water levels in the Monches Pond.  After the walls are formed, the top slab will be formed. Then the top slab will be reinforced with steel bars and poured.  Finishing the walls and top slab construction is expected to take about three weeks.

In the coming months Radtke still has much to do.  In May, Radtke will begin installing the gates of the dam, backfilling the dirt over the dam and then switching the river flow back through the new dam structure.  In June, Radtke will backfill the temporary diversion channel and begin restoring utilities and roadway and in July they will pave the roadway and install new beam-guard at both sides of the roadway.

Stay informed of the project’s progress by checking in at rasmithnational.com where you will see periodic project updates.


Questions?


Should you have any questions or concerns about the project status or project conditions, you may contact the Consultant Engineer, Jim Clements of R.A. Smith National at (262) 781-1000 or by email at james.clements@rasmithnational.com.

CTHE
A familiar scene on this project...lots of snow! Here the contractor hoists a sheet
pile with a crane and swings it into position to be driven into the
river bottom
.

2
With the structures cofferdam complete, two backhoes work in
tandem at the front of the dam to remove 4 feet of silt off the
river bottom. One backhoe excavates and the other loads the silt
into trucks to be hauled away.

CTHE
Looking at the foundation slab forming from front to rear; side
forms, bracing and reinforcement bars have been placed and are
ready for concrete. The reinforcement bar is coated with a green
epoxy coating to prevent the bars from rusting.

CTHE
Removing the Old Monches Dam with a backhoe. The old dam
was completely demolished and hauled away in 2 days.

4
The temporary diversion channel looking downstream. The large
heavy rocks placed in the river at each end of the channel is called
"rip rap". The rip rap prevents the channel from eroding away under
the turbulent river water.
CTHE
Radtke uses a backhoe to place the stone base layer. The base
layer allows subsurface drainage yet makes the perfect base for
the concrete foundation slab.

4
With the stone base material in place, Radtke installs the side
forms for the foundation slab. This is a view from the exit (apron)
side of the dam, looking towards the front of the dam.
CTHE
Concrete was placed using a telescoping truck-mounted conveyor
belt. The conveyor can be extended in or out and swings from
side to side to place the concrete exactly where it is needed.


 
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