This study presents the results of 32 laboratory experiments on local scour at a single pile and a 1 × 4 pile group for both uniform and non-uniform sediments under clear water conditions. The present study aims to evaluate the effects of different sediment beds made up of mixtures of sand and gravel (four-bed configurations) in d50 (1–3.5 mm) and gradation (1.4–3) ranges on scour depth for different flow discharges and flow depths. Further, the findings of the experiments are deployed to describe the effects of pile spacing and flow conditions on the local pier scour for both uniform and non-uniform bed granulometries. In addition, this study addresses the performance of some existing scourdepth predictors. Also, the corresponding results are suitable for validating the numerical models in local pier scour prediction importantly with non-uniform sediments. In summary, the results show that effects of sediment gradation dampen with increasing flow shallowness. Furthermore, the maximum scour depth at pile groups generally increases as pile spacing decreases for uniform sediments, whereas the mentioned trend was not observed for non-uniform sediments for the same flow and sediment conditions. Moreover, the experimental results revealed that bed sediment gradation is a controlling factor in the pile’s scour. Thus, the existing scour depth predictions could be highly improved by considering sediment gradation in the predictions. Finally, the conclusions drawn from this study provide crucial evidence for the protection of bridge foundations not only at the front pile but also at rear piles.
This article presents translations from the Nobel lectures for physics in 2017 given by all three laureates, who decided to use the same title, but each one focused on different aspects of the discovery. Weiss discussed the early history of gravitational waves and presented the concepts needed to understand the detectors as well as the challenges faced in measuring strains as small as 10-21. Barish describes how the LIGO project was organized to make steady improvements and ultimately carried out a successful scientific program. He describes signal detections as well as ideas of how to improve the detectors. Thorne presented the broader aspects of the new field of gravitational wave astronomy. He described the critical role of numerical relativity simulations and understanding quantum mechanics of precision measurements. He also gave a vision of the science that could come from an investigation of the gravitational wave sky from periods of fractions of milliseconds to tens of billions of years., Barry C. Barish., and Obsahuje bibliografické odkazy