Author(s): Nuele Defanti; Giancarlo Di Pasquale; Davide Poggi
Linked Author(s): Davide Poggi
Keywords: No Keywords
Abstract: The present study examines, through laboratory experiments, the effectiveness of collars in the protection of bridge piers against local scour. A number of collars, having the same circular shape but different dimension and distance from the bed, were studied. The experiments were conducted using several flow intensities, each of these in clear-water conditions. The cylindrical pier (D=30 mm) and collars (width of 2 and 3 time the pier diameter) were created in plexiglass. The flow intensity (U/U c, where U is mean velocity and U c is threshold velocity) was 0. 69, 0. 77, 0. 85 and0. 92. The duration of all experiments was 24 hours. To control the bed’s evolution around the pier in a continuous and non-intrusive way, an original technique of measure, based on a laser source and a high definition camera, was developed. A laser source was installed above the channel. The beam emitted from source is refracted by a cylindrical lens and opened in a vertical laser beam parallel to channel’s walls. This beam, positioned in the middle of channel, crosses the plexiglas pier and strikes the channel bed highlighting its geometry. A digital camera, controlled in remote by a laptop computer, was used to take a long sequence of photographs at chosen temporal interval. Results obtained have highlighted significant advantages in the use of collars in regard to configuration with simple pier, in terms of maximum scour depth’s reduction at upstream of pier (from 20% to 100% ), slowing down of scour rate and reaching the equilibrium in less time.
Year: 2010