Bridge scour is the leading cause of bridge failure all around the world, affecting significantly on the total construction and maintenance costs. Therefore, scouring around piers and abutments has been extensively studied in the past, focusing on point measurements of scour depth in front of a circular pier in alluvial sand beds. A literature review showed, that there is still a lack of studies on the effects of main scour parameters on the scour hole geometry, and on the mechanism of local scour around piers of different shape and alignment in gravel beds. This thesis attempts to fulfill this gap by experimentally investigating the development of scour holes around piers of different shape and alignment in gravel and sand beds. New non-intrusive, high resolution topography measurements of complete developing and equilibrium scour holes were performed during the experiments with an experimental installation using a laser distance sensor (LDS) and positioning systems. Additionally, the turbulent flow field around a square pier in gravel bed is measured with the acoustic doppler velocimeter (ADV) providing an insight into the complex flow field. The spatio-temporal variations of the geometric characteristics of developing scour holes are analyzed including the scour hole topography, time-dependent and equilibrium scour depth, scour extent, scour slopes and scoured volume. Firstly, the general observations made for each experiment are presented. All the obtained data are then analyzed in comparisons, as a function of the pier shape, angle of attack and sediment sizes. Empirical equations for the prediction of scour depth, scour radius and scoured volume as well as new pier shape and angle of attack adjustment factors were also obtained. Further, numerous prediction equations of time-dependent and equilibrium scour depths are evaluated. Effect of the pre-estimated experiment time on measuring and predicting the scour depth is also discussed.

Darmstadt, TU, Diss., 2011