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Numerical Model Evaluations of Cumulative Contraction Scour at a Bridge Site with Cohesive Soils
Date
2005-08-15Author
Harris, Dustin
Type of Degree
ThesisDepartment
Civil EngineeringMetadata
Show full item recordAbstract
The objective of this study was to perform 2-Dimensional numerical contraction
scour calculations at an actual bridge site with cohesive soils. The 2-D model used in the
analysis was the Finite Element Surface Water Modeling System (FESWMS) computer
program provided within the Surface Water Modeling Software (SMS). The study
presents the development of the model, the 2-D numerical transient contraction scour
calculation method, and a comparison of the 2-D contraction sour calculation results from
this study with 1-D numerical model results for the same bridge site presented in Curry et
al. (2003). The 2-D calculations are performed using velocity distributions and water
depths obtained from the FESWMS model along with the cohesive soil properties of the
bridge site presented in Curry et al.(2003). The cohesive soil properties used in the
calculations are the critical shear stress (tc), and the initial erodibility (Si) that were btained from soil tests using the Erosion Function Apparatus described in Crim (2003).
The model’s output of water velocities and water depths that vary in two perpendicular
horizontal planes provide the rest of the data needed for the calculations of the 2-D
distribution of scour in the contraction at the bridge site. This allows for the creations of
plan views of the predicted contraction scour, which is one of the primary advantages of
the 2-D model. The outputs presented in this thesis include plan views, cross-sectional
views, and longitudinal views of cumulative contraction scour for 5, 10, 50, and 100
days. The results are representative of how scour develops overtime using 2-dimensional
calculations. The Choctawhatchee River bridge site near Newton, AL is the focused site
of this study.
This study provides detailed information on how to set up a 2-dimensional
numerical analysis of contraction scour using FESWMS within SMS. The process for
calculating cumulative contraction scour at a bridge site with cohesive soil presented in
this study is one possible way for predicting scour. The actual application of this method
in the field of scour prevention and the development of new methods in bridge foundation
designs is still to be seen. More research and experimentation needs to be done along
with publications that promote these methods to the engineering field. This is a
continuation of ongoing research in the field of scour prediction in cohesive beds, and
presents methods and data that can be used for future research .