Bridge scour, which is the removal of bed materials from near the bridge
foundations, is observed to be the most predominant cause of bridge failures in the
United States. Scour in cohesive soils is greatly different from scour in cohesionless
soils owing to the differences in critical shear stresses, scour extents and the time taken
to reach the maximum scour depth in the scour process. The present solutions available
for the cohesionless soils cannot be applied to cohesive soils because of the above
crucial reasons. Also, a compound channel model with main channel and flood plain
arrangement represents more closely the field stream conditions rather than a simple
rectangular prismatic model.
In this study, a systematic investigation of the scour process due to flow
contractions in a compound channel with cohesive soil bed is made by conducting a
series of flume tests representing typical field conditions. The effect of the most crucial
factors causing contraction scour namely flow velocity, depth of flow and the shape of
the abutment is examined. Correction factors are developed for changes in flow geometries incorporating simulation results from the one dimensional flow simulation
model HEC RAS.
Most importantly, a methodology to predict the depth of the deepest scour hole
and its location in the vicinity of the contraction structure is developed for compound
channels through an extension of the presently available methodology to predict
maximum scour depths in simple rectangular channels. A prediction method to identify
the extent of the uniform scour depth is also developed. Finally, an investigation of
precision of the proposed methodology has been carried out on the field data from a
number of real life contraction scour cases.
The results obtained from this study indicate that depth of flow and geometry of
the contraction section significantly influence final scour depth in cohesive soils with
deeper flows and harsh contractions resulting in increased scour depths. However,
corrections for different contraction inlet skew angles and long contractions need to be
further explored in future studies.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2045 |
| Date | 15 May 2009 |
| Creators | Israel Devadason, Benjamin Praisy |
| Contributors | Chang, Kuang-An |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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