Experimental and Numerical Investigation of Local Scour for Suspended Square Caisson under Steady Flow

Abstract

A caisson can be suspended in the river during its settlement construction. The water flows induces the local scour of sediments under the caisson, which increases the settlement difficulty and threatens the safety of construction. A numerical model using computational fluid dynamics (CFD) was introduced to simulate the local scour process around the caisson. The numerical model was validated with a set of experimental tests, which were conducted to investigate the local scour for a square caisson model with different clearances under steady flow. The evolutions and characteristics of local scour pits as a function of clearance were investigated based on the experimental and numerical results. The effect of grain size of sediment and the scour mechanism for suspended caisson were discussed as well. The main findings include: 1) the minimum inflow velocity for the scour of sediment depends on the clearance between the caisson bottom and sediment; 2) the numerical model provides reasonable evolution of local scour pit and flow field around the caisson; and 3) the scour depth of suspended caisson can be as high as 70% of that for the settled caisson and deserves attention for the safe settlement of caisson.