Experimental investigation of local scour under two oblong piers of a bridge crossing a sharp bend river

Abstract

Bridges built across a river bend and supported by more than one pier has been experimentally studied regarding the shape and nature of erosion and deposition. For this purpose, a U-shaped laboratory channel was used with two oblong piers installed at different locations. The first one was at the mid-section of the upstream straight reach, whereas in the second site within the bend, the piers have been installed at sections of central angles 0°, 30°, 60°, 90°, 120°, 150°, 170°, and 180°, from the beginning to the end of the bend segment respectively. The studies were conducted under clear water and threshold flow conditions. The results show that the higher and lower values of local scour around the pier positioned close to the outer bank, are 1.803 and 0.623 times the pier width when the bridge was installed at an angle of 90° and 30° respectively. As for the pier close to the inner bank, the deepest local scour was 1.786 times of the pier width when the bridge was installed at 60° of the bend, while the least one was 0.516 times of the pier width when the bridge was located in the 180° sector. It is worth noting that the presence of piers within sector 150 is less affected by local scour than in the other sections.