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42
ALTERNATIVE EVALUATION FOR PROPOSAL NO.
1C
PROJECT:
Chicago Ditch Dam Rehabilitation
COMPONENT:
Diversion Dam
FUNCTION:
Divert Water
ALTERNATIVE DESCRIPTION
Construct the diversion dam crest and slopes using grouted riprap and
eliminate the new sheet piles and reinforced concrete. The primary features
of this alternative are:
1)
A 3-foot layer of grouted riprap would form the crest and slopes of the
diversion dam. The crest would have a 12-foot width and the upstream
slope would be 3 to 1. The downstream slope would be 6 to 1. The grouted
riprap would tie into the existing two rows of sheet piles.
2)
A geotextile would be placed under the crest and downstream portion of
the grouted riprap to provide filter protection in the event cracks form
in the grouted riprap.
BENEFITS
DISADVANTAGES
Construction (although not as
simple as Alternative 1A) will be
faster than the original proposal.
Therefore, some operational time
would be saved.
The crest would not be as smooth as
the Title I proposal but will still
be accessible to foot traffic and
maintenance vehicles.
The upstream face will have a rough
surface. This may make removal of
small debris more difficult.
Additional investigation into
condition of existing sheet pile
would be necessary.
IDENTIFIED RISKS:
If removal of smaller debris is required, it may become lodged in rough
surface and necessitate more effort.
This option will tie into existing sheetpile in a method similar to the Title
I design. If the investigation determines that the present condition of the
existing sheetpile is unsuitable for the proposed use, a new sheetpile wall
costing about $120,000 would be necessary.
VEALTEVL.ALT