Stability Analysis of Composite Breakwaters Under Seepage Flow

The effect of seepage flow on the bearing capacity of the mound for composite breakwater was investigated using a coupled fluid analysis and ground deformation analysis. To examine the validity of the coefficient of resistance from porosity in the previous formula, numerical permeability tests in a U-tube were conducted using a fluid analysis. As a result, seepage flow velocities due to Kadlec and Knight’s formula agreed well with Creager’s experimental data. Next, the effect of seepage flow on the effective stress at the mound of the breakwater due to the water level difference was examined. The results showed that the effective stress did not decrease significantly due to a seepage velocity at around 0.01 m/s, while a slight decrease in the effective stress behind the caisson was observed. There are two possible reasons. One is that the seepage velocity is small in this study, and the other is that the acceleration term of the seepage velocity is neglected in our basic equations. However, it has been pointed out that in the u-P form, the acceleration term of the seepage flow is neglected, which causes the calculation to fail when the seepage flow velocity increases.