Date of Award

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Civil Engineering

Advisor

Dr. Abdul Khan

Committee Member

Dr. Sez Atamturktur

Committee Member

Dr. Nigel Kaye

Committee Member

Dr. Lawrence Murdoch

Abstract

Scour is one of the most significant threats to bridge infrastructure and is the leading cause of failure within the United States. Given this risk to the nation’s transportation infrastructure, it is necessary to understand the development of scour holes around bridge piers and abutments. This can be achieved with scour monitoring, a Federal Highway Administration approved scour countermeasure. As the monitoring techniques available range from simple devices that rest on or in the channel bed to advanced scanning systems that provide a bed contour profile, a concise study of the state of the art in real time scour measurement capabilities is required. This is accomplished in this work, along with the development of a scour monitoring technique that is show to provide reliable information during a wide variety of channel conditions. The current technologies available for monitoring scour are reviewed to highlight the governing physics, to evaluate the field performance, and to identify the effect of environmental factors on the performance. From this assessment, two devices are selected for further study; a sonar fathometer and a time domain reflectometry device. Several environmental factors are highlighted that influence these devices, including channel temperature, salinity, and suspended sediment concentration. A novel device is proposed which exploits the turbulence in open channels as a means of monitoring the bed level. The device uses a sensor that is sensitive to the dynamic pressure due to the natural turbulence in open channels. This sensor vibrates at a significantly higher magnitude when in the channel flow relative to an identical sensor located in the sediment. The vibration-based method, time domain reflectometry, and sonar devices are then evaluated against simulated field conditions in order to determine their relative sensitivities to environmental conditions. These tests reveal that sonar and time domain reflectometry devices can be influenced by channel salinity and temperature. In addition, the sonar device is shown to be sensitive to the suspended sediment concentration in the channel. The vibration-based method is shown to be insensitive to the suspended sediment concentration as well as bed sediment type. The effect of flow angle is also evaluated for the vibration method, and reveals that the novel device operates in highly misaligned flows. Lastly, an analytical model is built for further optimization of the device. The model is then verified, calibrated and validated with experimental data. The validated model is used to develop a field prototype, which is tested experimentally and reveals satisfactory performance for deployment to bridge sites.

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