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The results of laboratory experiments on scour around circular piers in cohesionless bed material at high Froude numbers, F, up to 1.5 are presented. The scour depths in sediment transport regime (F is greater than F sub c) first slightly decreases and then increases with the increase in the Froude number. A formula to predict the scour depth at Froude numbers (F-F sub c) is equal to or greater than 0.15, is developed. The limitations of some of the existing predictors of local scour are discussed, and a new formula to predict the maximum clearwater scour is proposed.
Bachelor Thesis from the year 2019 in the subject Physics - Mechanics, University of Engineering & Technology Peshawar, language: English, abstract: The objective of the study is to conduct laboratory model testing to investigate and compare scour hole depth of the diamond, square and elliptical scaled model of bridge piers in a cohesion less bedding material under clear water and to propose the most efficient cross section of the bridge pier, having less Local scour around piers under steady clear-water condition was studied experimentally for a variety of configuration, including different sizes and shapes of piers. Total number of forty experiments were performed in the flume using diamond, square and elliptical shape. The scouring around the square shape was found maximum and at elliptical shape was the least. The main reason was obstruction in flow area that was more in case of the square and less in case of the elliptical shape. However, the diamond shaped has the intermediate scouring under same condition. Local scour is a complex phenomenon involving three-dimensional flow, typically developed around piers founded in movable bed rivers. Local scour can lead to partial failure or to collapse of bridge piers because of the high flood velocity. The cost of large bridges, with common and special complex piers, justifies carrying out an accurate prediction of scour depth, for both economic and safety reasons, which in turn leads to the interest of hydraulic engineers in predicting the equilibrium scour depth.
Local scour around piers and abutments is one of the main causes of the collapse of many bridges constructed inside rivers. Many researchers have conducted various studies to predict the maximum depth of a scour hole around bridge piers and abutments. However, most of them have been done in small-scale laboratory flumes and specifically for the open channel condition. Besides, most of the existing research on bridge piers uses uniform sediment which is not an appropriate representative of natural river systems. This can result in excessively conservative design values for scour in low risk or non-critical hydrologic conditions. The most severe cases of bridge pier scouring occur in cold regions when the surface of water turns into ice in which, an additional boundary layer is being added to the water surface, which leads to significant changes in the flow field and scour pattern around bridge piers. Ice cover also causes the maximum flow velocity to move closer to the channel bed.
"A comprehensive state-of-the-art treatment of scour and bridge foundations - both a handy reference text and a manual for the practicing bridge designer."--Publisher.
"Ice cover imposes an additional boundary layer on a river channel and can influence sediment transport around bridge structures. The main objective of this study was to gain a better understanding of how ice cover is related to local scour around bridge piers. A set of flume experiments were completed investigating local scour around bridge piers under open channel, smooth ice and rough ice cover conditions. Three different non-uniform sediments were used with D50??2019?s of 0.47, 0.50 and 0.58 mm. The location of the average maximum velocity under rough ice cover ranged from 0.36-0.43H and for smooth cover was 0.41H, with depth (H) measured from the channel bed to water surface. Turbulent intensity was greater under ice cover than open channel conditions. Local pier scour under rough and smooth ice cover was on average 37 and 20 percent greater than open channel scour depth respectively. The maximum scour depth always occurred at the pier face. Greater pier scour under ice cover is related to larger streamwise and downward flow velocities at the pier face under rough ice cover. The scour hole velocity for rough and smooth ice cover was 33 and 15 percent greater than open channel scour hole velocity respectively. Under all channel covers an armour layer formed in the scour hole. For all experiments, as the armour layer size increased, the maximum local scour depth decreased. A critical assessment of current bridge research and construction was also conducted in order to address how this study contributes to modern day bridge design. It was found that this study addresses current knowledge gaps in bridge manual used in North America. Specifically, study results concerning scour hole depth under ice cover and scour hole flow fields under ice cover are important contributions to the field of bridge hydraulics."--Leaf ii.
Information and technical data concerning scouring/erosion caused by water fl in rivers and streams. More specifically, how certain structures exaggerate this natural process by restricting water flow, causing constriction and loc scour. Material presented is from both field studies and laboratories
Amid increasing interactions with other disciplines and technical advances for detecting, monitoring, and modeling fluvial landscape origin, dynamics, and diversity, a number of scientific works have come out and nested in globally recognized edited books. This book is an attempt in this regard, where a few precise regular research works from diverse disciplinary expertise from around the globe are compiled as chapters. In this collective effort, the application of geoinformatics, field data on natural rivers, instrumentation, use of analytic tools, scientific techniques, numerical models, case studies, illustrations, etc. in understanding formative processes and appraising fluvial landscapes will hopefully provide insight into the current practice of fluvial geomorphology and may guide fruitful and coherent scientific enquiry into the field.