3D jet scour at a wall

• Main Author: Chow, Stephen Guang Wei
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/141715
• Institution: Nanyang Technological University

Scouring is a phenomenon of sediment transport caused by flowing water. In berthing harbors, the sediment bed located at the toe of the quay walls provides necessary passive earth pressure to prevent geotechnical failure of the walls, such as slipping or overturning. This sediment bed is highly susceptible to scouring actions by bow thrusters from ships, which may result in a significant amount of bed erosion at the toe of these walls and compromises its stability. Hence, it is imperative to understand the possible magnitude of the localized scour hole formed, in order to determine an optimal design of bed protection at the toe of the quay walls to prevent severe erosion. This study examined the effects of various hydraulic variables on a confined jet scour at a wall and unified the data through dimensional analysis and multiple regression techniques. A suspended circular horizontal jet was directed at an obstructive wall to simulate the scouring effects of berthing ships at a quay wall. The independent variables tested include the velocity of the water jet, offset height of the suspended jet from the sediment bed, horizontal distance of the suspended jet from the wall, as well as size of the sediments used. The presence of the wall provides deflection of the water flow back towards the sediment bed, generating additional scouring actions. It is observed that the dimensions of the scour hole formed are larger as the velocity of the jet increases and the size of the sediment decreases, while the offset height of the jet from the sediment bed does not significantly affect the size of the hole. As the distance of the jet from the wall increases, the dimensions of the scour at the foot of the wall decreases. The experimental results were compared with equations proposed by Tan (2018), Chiang (2019) and Yuksel et al. (2019). When the results of the current study were compared with the proposed equations, the data points deviate significantly from the line of perfect agreement. Using regression analysis, this study proposes new empirical equations to determine dimensions of scour hole at the foot of the wall, with high R2 value of 0.881 – 0.902.