Transcript Peggi Knight--Iowa

2014 AASHTO High Value Research
Peggi Knight
Research conducted by
Center for Earthworks Engineering (CEER),
Iowa State University
Problem:
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Full year’s worth of rainfall in one month.
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More than 200% above normal snowpack in Rockies.
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Longest duration flood event in US History.
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At the height of the flooding a 75-mile stretch of
Missouri River had no open crossing in Iowa.
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At some locations in Iowa water flowed several feet
deep over roadways for more than four months.
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Approximately 60 miles of IA state and interstate
highways and over 100 miles of county (secondary)
roadways were closed.
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Obvious Damage
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Stripped overlays
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Delaminated Surfaces
Understanding the damage we can not see
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Unknown voids
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Damage to bridge foundations and culverts
Determining when to open roads up to traffic
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Saturated embankments
Office of Research and Analytics
• Objectives
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Asses the damage to the geoinfrastructure on affected local
roadways
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Develop effective repair and
mitigation strategies
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Develop emergency response
criteria
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Develop a guide for flood
damage assessment for future
flood events
Western Iowa Missouri River Flooding
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Tests to evaluate roadway support capacity, embankment conditions,
and settlement problems
 GPR, FWD, DCP
 Soil shear strength
 Shelby tube samples for lab analysis
Monitor performance of the flooded versus un-flooded areas by
evaluating subsurface foundation layer performance characteristics over
time.
Visual flood water boundaries (aerial images, dead grass, damage to
gravel surfaces, shoulders and chip seals) do not equate to saturated
roadway embankment limits.
Water flow through the road foundation layers – erosion, consolidation,
creation of weep holes.
Western Iowa Missouri River
Flooding
Google images were used to help identify flood boundaries by
comparing pre-flood (6/28/2010) imagery and during flood
(7/17/2011) images
Western Iowa Missouri River
Flooding
Weep holes (approx. 4 in.) found at one culvert inlet. Similar weep
holes found at other culverts. Some culverts had as many as 20
weep holes.
Western Iowa Missouri River Flooding
FWD plate depression at one of the test segments
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FWD testing of some locations showed up to a 52% decrease in
modulus – DCP testing showed it is due to loss of foundation
support.
Field testing identified differences in road support conditions in
flooded versus un-flooded areas (saturated vs. unsaturated).
The FWD and DCP tests provided valuable subsurface
information to characterize support conditions.
Understanding the performance differences between flooded
versus un-flooded road segments based on engineering
measurements could be useful as part of the process to define and
prioritize areas for repair.
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Catalog of field assessment techniques, descriptions
and guidance
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20 potential repair/mitigation solutions with
descriptions and guidance
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Flow chart relating damages observed, assessment
techniques, and potential solutions
These options are discussed for paved and unpaved
roads, culverts, and bridge abutments.