Bridge failures are generally resulted from scour of the bed material around bridge piers and abutments during severe floods. In this study, scour phenomenon around bridge abutments and collars, located at abutments as scour countermeasures, were experimentally studied. The experimental study was carried out under clear-water scour conditions with uniform non-cohesive sediment (having a grain size diameter of d50=0.90 mm). The experimental flume is a rectangular channel of 30 m long and 1.5 m wide filled with this erodible bed material. Based on the results of 97 experiments conducted during the study, the efficiency of various sizes of collars, which were used to reduce the local scour depth, located at different elevations around the abutments was determined. The results obtained were compared with previous studies, and the effect of the sediment grain size on the performance of abutment collars was emphasized. It was noticed that when the collar width was increased and placed at or below the bed level, the reduction in scour depth increases considerably. It was also found out that the change of the sediment size did not affect the optimum location of the collar at the abutment, which yields the maximum scour reduction around the abutment.

During severe floods, bed material around bridge piers and abutments are scoured by the flow and as a result, bridges are subject to damages. These damages are mostly unrepairable and can result in loss of lives and property. In this thesis study, abutment scour under clear-water condition was investigated and collars were tested as scour countermeasures around the abutments. The experimental study was carried out in a rectangular channel with an almost uniform cohesionless bed material of d50=1.50 mm for a test period of 3-hours. The channel was 28.5 m long and 1.5 m wide. The erodible bed material was placed into the test section that was 5.8 m long and 0.48 m deep. For this thesis study, 60 experiments were carried out with and without various collars placed at different elevations around the abutments. The scour formation around the abutments with collars was observed and scour reduction efficiencies of the collars were studied. Experiment results were compared with the previous studies of Dogan (2008) and Kayat&uuml / rk (2005) in terms of sediment size, abutment shape and flow depth, and the effects of these factors on collar&#039 / s scour reduction efficiency were studied. Based on the results of the experimental studies, it was observed that scour depths decreased as the collar width increased and the collar placed deeper into the sediment bed for a given abutment length. When the present study and the previous studies were compared, it was observed that sediment size and flow depth had no significant effect on the scour reduction performances of the collars.

The major damage to bridges occurs due to scour of the bed materials around piers and abutments during severe floods. This study involves the experimental investigations of the various scour patterns forming around abutment models tested with and without collars as scour countermeasures. The experiments were conducted in a rectangular channel under clear-water scour conditions. In the first part of this study, 34 experiments were conducted with semi-circular end abutment models with and without a collar for a period of 3 hours. Collars of various sizes were placed at different elevations on the abutment models, and the scour reduction efficiencies of collars were investigated for the different flow depths. Based on the results of the experimental studies, the optimum locations of collars on the abutments, which result in minimum scour depth around the abutments, are obtained at the bed level and below the bed level depending on the flow intensity values. In the second part of this study, the effects of flow depth and abutment length on the temporal development of local scour at bridge abutments were studied. 20 experiments were performed without collars for a time period of 8 hours. It was observed that at the upstream of the abutment, the depth of the local scour increases rapidly within the first three hours of the experiment for the different flow depths.

Samples collected from 5 bridge sites from around the state of Georgia are analyzed to determine their erosion and rheologic behavior. Most sites were subject to large amounts of local scour due to flood events resulting from Tropical Storm Alberto in 1994. According to the Federal Highway Administration's Hydraulic Engineering Circular No. 18 by Richardson and Davis (2001), scouring of bridge foundations is the most common cause of bridge failure resulting from floods. The erosion rates of the soils are measured in a rectangular tilting flume capable of applying up to 21 Pa of shear stress at the bed. Samples from Shelby tubes are extruded into the flow from below the bed using a hydraulic piston. The displacement is measured as a function of time using a cable-pull potentiometer. The soils are also subject to extensive geotechnical analysis. Sieve and hydrometer analyses are performed to obtain the particle size distribution for each sample. Atterberg Limits and other standard geotechnical measures are also found. Additionally, insight into the shear strength and cohesive nature of the fine (<0.75 micrometers) particles is gained using a stress controlled rheometer to measure the rheological characteristics of the slurry. These results are used to improve and extend a relationship for the critical shear stress of soils developed in previous research that can be used in bridge scour prediction formulae as affected by soil parameters. In addition, the rheologic properties of the soil in terms of a dimensionless yield stress are related to the critical value of the Shields parameter for estimating critical shear stress for erosion.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / This paper, evaluates a proposal for an external bend fluvial erosion control, using submerged vanes as velocity and shear stress control, verifying its effectiveness by modeling in Iber to calculate the scour produced by discharges with different return periods. The results indicate that the velocity, shear stress and scour decrease along the curve, due to submerged vanes.

The Utah Department of Transportation commissioned a study to determine whether or not shallow-flow rock structures could reliably be used at bridge abutments in place of riprap. Research was conducted in a two-phase effort beginning with numerical modeling and ending with field verification of model findings. As part of phase one, two finite element meshes were created in Surface-water Modeling Software (SMS) and analyzed with FESWMS-2DH. Second, field studies were conducted and a preliminary database was developed to track field studies conducted on 98 shallow-flow rock structures in Utah. Data organization in ArcGIS® and Microsoft Access® is presented followed by instructions on how to use the database. Both numerical model and field research results indicate that shallow-flow rock structures are not viable scour countermeasures at bridges.

Yes / Pier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman's equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo's and Kim et al.'s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman's equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors.

Yes / Pier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman’s equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo’s and Kim et al.’s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman’s equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors.

Yes / Laboratory experiments are presented to investigate the effect of different piggyback pipeline configurations on the morphology of local scour under wave conditions. Scour depth and width around the pipelines under regular and irregular waves are measured and analyzed for a range of pipeline and wave conditions; such as the spacing between two pipes (G), gap between the main pipe and seabed (e), pipe diameter (D), wave height (H) and period (T). Experimental results reveal that both the scour depth and width around piggyback pipeline is much larger than those around single pipe under the same wave conditions. Scour depth increases with the increase of the Keulegan-Carpenter (KC) number and decreases with increase of G and e. When e exceeds 0.5D, scour depth tends to approach 0.When spacing G is greater than 0.4D, the destabilization from small pipe to large one is greatly reduced, resulting in scour depth around piggyback pipeline being close to that around single pipe. Similar to scour depth, scour width broadens with the increase of KC number increasing and decreases with the increase of G. Experiments also show that the effect of e on scour depth is greater than that of G under the same test conditions, while their impact on scour width is opposite. Furthermore, scour width under irregular waves is extended slightly compared with regular wave for otherwise the identical conditions. / National Natural Science Foundation (No. 51279189).

Extreme rainfall events associated with global warming are likely to produce an increasing number of flooding scenarios. A large magnitude of hydrologic events can often result in submerged orifice flow (also called pressure flow) or embankment and bridge overtopping flow, in which the foundation of a bridge is subjected to severe scour at the sediment bed. This phenomenon can cause bridge failure during large floods. However, current laboratory studies have focused on only cases of free-surface flow conditions, and they do not take bridge submergence into account. In this study, abutment scour experiments were carried out in a compound channel to investigate the characteristics of abutment scour in free-surface flow, submerged orifice flow, and overtopping flow cases. Detailed bed contours and three components of velocities and turbulent intensities were measured by acoustic Doppler velocimeters. The results show that the contracted flow around an abutment because of lateral and/or vertical contraction and local turbulent structures at the downstream region of the bridge are the main features of the flow responsible for the maximum scour depth around an abutment. The effects of local turbulent structures on abutment scour are discussed in terms of turbulent kinetic energy (TKE) profiles measured in a wide range of flow contraction ratios. The experimental results showed that maximum abutment scour can be predicted by a suggested single relationship even in different flow types (i.e., free, submerged orifice, and overtopping flow) if the turbulent kinetic energy and discharge under the bridge can be accurately measured.