Author(s): Jana Zaidan; Adrien Poupardin; Abdelkrim Bennabi; Francois Marin; Ahmed Benamar

Linked Author(s): Jana Zaidan, adrien Poupardin, Abdelkrim Bennabi, François Marin

Keywords: Laboratory experiments; Instrumentation; Monitoring; Scanner Laser; Local scour; Pier

Abstract: Laboratory experiments constitute an essential part of scour investigation in the vicinity of embedded structures. The previous studies reported a variety of prediction methods but to date without any standard and robust instrumentation for monitoring the development of this physical phenomenon during tests. Traditional methods based on placing point gauges in the bed [1] provide only a punctual measurement and are not suitable for global dynamic process. Other methods using miniature video camera inside a hollow calibrated pier [2] are less usual at small scales. Profilometer laser [3] is time consuming in post treatment of data and require complex mounting system. In this technical paper, a Scanner Laser has been tested for following local scour around circular pier (D=32 mm) embedded in a layer of uniform non cohesive soil (d50= 1.7 mm) at clear water condition with ratio between the current velocity and critical velocity of incipient motion of sediment Vx/Vcr=0.7, Reynold number based on the height of the flume Re= 42920, Froude number Fr= 0.24 and Reynold number based on the diameter of the cylinder ReD= 9280 in hydraulic flume, to demonstrate its efficiency. This new technology consists of a pattern projector and a camera which provides 3D points clouds at maximum frequency rate of 0.5 Hz by using triangulation method. These points clouds are then treated to correct effects of refraction between interfaces and replaced in a local orthonormal system centered onto the pier. The results validate the performance of this technique which is being in good agreement with previous studies. The initiation of local scour is observed at the sides of the pier. The maximum final scour is close to the pier diameter. Finally, the greatest advantages of this technique with regards to others, are the data acquisition rate, especially at the beginning of the experiment, the accurate continuous spatiotemporal resolution with dense data and the set-up flexibility which can be a tripod. However, the limitations are related to the choice of the device position due to the high probability of having shallows and the loss of accuracy in certain positions of the instrument in case of steep slopes. In addition, measurements are not possible in presence of suspended sediments creating high water turbidity. [1]R. M. Lança, C. S. Fael, R. J. Maia, J. P. Pêgo, and A. H. Cardoso, “Clear-Water Scour at Comparatively Large Cylindrical Piers,” J. Hydraul. Eng., vol. 139, no. 11, pp. 1117–1125, 2013, doi: 10.1061/(asce)hy.1943-7900.0000788. [2]K. Debnath and S. Chaudhuri, “Bridge Pier Scour in Clay-Sand Mixed Sediments at Near-Threshold Velocity for Sand,” J. Hydraul. Eng., vol. 136, no. 9, pp. 597–609, 2010, doi: 10.1061/(asce)hy.1943-7900.0000221. [3]F. Lachaussee, “Érosion et transport de particules au voisinage d ’ un obstacle,” 2019.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022751

Year: 2022