Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Khan, Abdul

Committee Member

Atamturktur , Sez

Committee Member

Ravichandran , Nadarajah

Abstract

Scour around bridge piers and abutments, is the prominent reason for bridge failures. Bridge failures have substantial effects on economy and human lives. About 60% of the total bridge failures in U.S. can be attributed to scour. In the past, scour has been responsible for several million dollars in bridge repair cost. Given the threat to the bridge infrastructure due to scour, the U.S. Federal Highway Administration has proposed several countermeasures to reduce the impact of bed degradation. One of these countermeasures that is particularly relevant during peak flow periods is the real-time scour monitoring. Scour monitoring involves real-time data collection to assess the progress of scour holes. Two of the most common scour monitoring systems are sonar/fathometers and time domain reflectometry. This manuscript focuses on these two best in the class techniques to evaluate the effects of channel conditions on the accuracy of these systems. Through an extensive experimental campaign, the performance of these two monitoring techniques under different channel conditions, such as water temperature, salinity, and sediment concentration, is evaluated. The experimental results indicate that both time domain reflectometry and sonar methods are sensitive to the channel temperature and salinity. For a sonar device, such effects can be accounted for by modifying the speed of sound for different temperature and salinity levels. For the time domain reflectometry method, the temperature effects can be accounted for by using the same approach, while salinity degrades the waveform features limiting the device to non-saline environments. Furthermore, the time domain reflectometry is observed to be insensitive to suspended sediment concentrations and turbid flow. Sonar, however, is found to be sensitive to the combined effects of moving turbid water. As the velocity of turbid water increases, the standard deviation in the sonar measurements increases. Eventually reaching a point at which the device can no longer yield an accurate reading of the bed. In addition to the impact of temperature, salinity, and suspended sediment, the sonar is also sensitive to additional operational conditions within the channel. Sonar is also tested in varying bed topography conditions to assess the impact of beam radius. The result reveals that the device records the minimum depth within the beam diameter. In nature, channels flow under diverse conditions. So it is of great significance to evaluate which scour monitoring system is suitable under given conditions. Based on the results of experiments performed in this study, appropriate scour monitoring system can be chosen for a given channel conditions.

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