Experimental Study of Local Scour around Caissons under Unidirectional and Tidal Currents

Abstract

Local scour around caissons under currents has become one of the main factors affecting the safety of foundation construction and operation in coastal and offshore bridge engineering. Local scour occurs not only in the operation stage, when the caisson has settled into the sediment, but also in the construction stage, when the caisson is suspended in water. In this study, the local scour induced by unidirectional and tidal currents around settled caissons with different cross-sections (circular, square, and diamond) was experimentally investigated. Circular and square caissons were selected to investigate the difference in local scour of suspended caissons under unidirectional and tidal currents. The main findings from the experimental results were: (1) the temporal development of scour under tidal current was slower than that of unidirectional current; (2) the effect of current type can significantly influence the size and location of maximum scour depth around circular and square caissons; (3) the appropriate choice of cross-section could reduce the maximum scour depth around the settled caisson; (4) the maximum scour depth of tidal current was smaller than that of unidirectional current when the caisson was settled into the sediment, while the opposite effect occurred when the caisson was suspended in water.

Influencia de la granulometría, forma de pila y parámetros hidrológicos en la socavación

“…Lo contrario sucede al variar la pila a una redondeada, donde sí se presentan cambios en la erosión de estos tipos de materiales. Esto se debe, en términos generales, al hecho de que sobre la cara de la pila cuadrada se concentra mayor energía; según los resultados de investigaciones recientes de Du y Liang [34] y Xiang et al [35], la resistencia del suelo al transporte depende más de su gradación (entrabamiento), que del contenido de partículas finas.…”

Geotechnical Approach to Early-Stage Site Characterisation of Shallow Wave Energy Sites

“…The sediment transport in the area is likely onshore-offshore with little tidal flow and rocky reefs surrounding the region. Recent studies such as Lancaster et al [30] and Qiqi et al [31] demonstrated that significant scouring on a square caisson can occur at all four corners. Scour could hamper the integrity if sediments were removed from underneath the structure at specific points causing a seaward tilt and settlement, especially in such an energetic shallow water environment with poorly compacted sand and velocities near the bottom exceeding values of 1 m/s.…”

Bridge headwater afflux estimation using bootstrap resampling method

“…The stream hitting the bottom causes the horseshoe vortices formation (3 in Fig. 1) [4,5]. Initial vortices are formed, eventually taking the form of a lee-wake vortex (4 in Fig.…”

“…Three stages of the scouring process can be distinguished: the initial stage related to the scouring initiation, the proper stage, which is the period of scour development and deepening, and the final stage, in which the shape stabilization could be observed. The most significant initial stage could be pointed to, which is characterized by the high stream velocities occurrence in the bottom region and high stream turbulence [4][5][6][7][8]. The water surface elevation along the river reach depends not only on the hydraulic structure properties but also on the local granulometric conditions, which can be quantitatively characterized by hydraulic resistance coefficients.…”