Identifier

etd-08222011-173310

Degree

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

The overall goal of this research is to evaluate the applicability of the existing HEC-18 method to Louisiana bridges that are mostly situated on cohesive soils and hence to develop a more reliable design method for scour depth and scour rate prediction. Pier research in sandy soils and cohesive soils shows that the sandy soils are known to erode particle by particle, while cohesive soils usually erode in clumps rather than individual particles, which is caused by from the different bonding mechanisms between sandy soils and cohesive soils. Because the bonding in cohesive soils is so complex, the prediction of scour depth in cohesive soils is more difficult and no such a set of equations have been widely accepted. In order to study the influence of soil types on scour depth prediction in Louisiana, totally seven bridges situated on clays, silts, and sands were selected as case studies for scour analysis over a 10-15 year period. The hydraulic properties were determined by analyzing satellite remote sensing data, which were then used as input to HEC-18 method via a software program WASPRO. The recorded scour survey data were also analyzed and compared with the results obtained by the HEC-18 method using the real flood data. Significant discrepancy exists among the HEC-18 prediction and surveyed scour depth, and the predicted values are always greater than the surveyed depth. Therefore, for cohesive soils, the HEC-18 method usually provides a more conservative design. Although the bridges are safe for the final scour depth, the HEC-18 method typically yields a more costly design.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Tsai, Frank

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