Stability of caisson-type breakwater foundation under tsunami-induced seepage

A tsunami-induced difference between the water levels of the seaward and the landward sides of breakwaters generates one-way seepage in the rubble foundation under the breakwaters. Such seepage may decrease the bearing capacity of the rubble foundation, trigger the piping and/or boiling of the foundation, and cause the scouring of the sandy seabed. In this paper, we describe the stability of a breakwater foundation under the action of seepage based on the results of model tests and FEM analyses. The main feature of our study is the application of the centrifuge technique to such composite hydrodynamic and geotechnical problems. The centrifuge technique can be used to produce high-water pressure and ground stress corresponding to those of prototype-scale breakwaters. The experimental results show that seepage-induced scouring and boiling occur, and that the seepage force decreases the bearing capacity of the rubble foundation. The results of the numerical analyses also reveal the effect of the reduction in bearing capacity in the presence of seepage.