Scour at the Base of Hydraulic Structures: Monitoring Instrumentation and Physical Investigations Over a Wide Range of Reynolds Numbers

Hydraulically induced scour of the streambed at the base of bridge piers is the leading cause of bridge failures. Despite the significant scientific efforts towards the solution of this challenging engineering problem, there are still no reliable tools for the prediction and mitigation of bridge scour. This shortcoming is attributed to the lack of understanding of the physics behind this phenomenon. The experimental studies that attempted the physical investigation of bridge scour in the past have faced two main limitations: i) The characterization of the dynamic interaction between the flow and the evolving bed that is known to drive scour, was not possible due to the limitations in the available instrumentation and the significant experimental difficulties; ii) Most of the existing literature studies are based on the findings of laboratory experiments whose scale is orders of magnitudes smaller compared to bridges in the field, while the scale effects on the scour depth have never been quantified. The objective of this research was to enhance the existing understanding of the phenomenon by tackling the aforementioned experimental challenges. To accomplish this, the first part of this work involved the development of a new underwater photogrammetric technique for the monitoring of evolving sediment beds. This technique is able to obtain very high resolution measurements of evolving beds, thus allowing the characterization of their dynamic properties (i.e. evolving topography and scour rates) and overcoming existing experimental limitations. Secondly, the underwater photogrammetric technique was applied on a bridge scour experiment, of simple geometry, and the dynamic morphological characteristics of the phenomenon were measured. The detailed measurements along with reasonable comparisons with descriptions of the flow, from past studies, were used to provide insight on the interaction between the flow and the bed and describe quantitatively the mechanisms of scour. Finally, the scale effects on scour were studied via the performance of two experiments under near-prototype conditions. In these experiments the effects of the Reynolds number on the flow and the scour were quantified and implications concerning existing small-scale studies were discussed.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Civil Engineering

Department dc:contributor.department

Civil and Environmental Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2015

Author dc:creator

• Bouratsis, Polydefkis

Chairs dc:contributor.committeechair

• Dancey, Clinton L.
• Diplas, Panayiotis

Committee members dc:contributor.committeemember

• Grizzard, Thomas J.
• Stark, Nina
• Kriz, Ronald D.

• scour
• bridge hydraulics
• loose boundary hydraulics
• horseshoe vortex
• junction flows
• physical modelling
• underwater photogrammetry
• acoustic Doppler velocimeter

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

vt_gsexam:3885

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/71880