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Determining Strength of Levee
Name: Morgan
Status: student
Grade: 6-8
Location: NC
Country: N/A
Date: 10/25/2005
Question:
If and when they fix the levee in Louisiana, how will
they measure if it is repaired? What devise can be used to measure it?
How will you know it is repaired?
Replies:
Hi Morgan,
I think that your question really has two parts to it. First, the levee
was intended to hold back the water from flooding the city. The levee
can be considered repaired when it is restored and it is holding back
the water under normal conditions. Engineers can calculate the
pressures on the levee due to the water and build accordingly.
The second part, and what I think you are really asking, is "How do we
know that the new levee with withstand another Hurricane?" The answer
is that we will never know until it happens again. Engineers can try
and estimate what pressures and forces the levee might encounter, but
mother nature is powerful and unexpected.
Bob Hartwell
The design relies on sampling the underground soils,
computer models to determine the wave heights and forces.
Then computations to determine the width of the base, the
slopes of the sides and the top width are made. The properties
of the fill used to form the levee are known. The construction
is monitored and samples taken. As with anything that is made,
if all the specifications and drawings are followed, there is the
confidence that it will work. When it comes to soils, there can be
localized failures, settling or sloughing off. So, there is monitoring
to identify spots needing repair. For existing levees when there
are patches etc. the assumptions and computations become complicated.
What part is old and in what shape.
To measure performance, the levees themselves may contain
equipment which can record the moisture, or condition of the soils.
An example, consider snow , you can tell "good packing" for snow balls,
that is the percent of moisture present. Dry fluffy snow does not
make "good packing". Equipment can measure the water content in
the levee. Think of the houses in California that slide down the hills,
during the heavy rains. The failure is in the water filling the pores
between the soil particles, so levees can be monitored, but during the
hurricane,
the conditions are life threatening to go out and read gauges,
and reading devices removed from the site, rely on electricity, which can go
out.
So, often, you have to wait till the storm passes to check them.
James Przewoznik
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Update: June 2012
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