Wave pressure reduction on vertical seawalls/caissons due to an offshore breakwater

The technique to reduce the wave loads on seawalls/caissons is gaining momentum around the world. Placing an offshore structure in front of seawall/caisson is expected to reduce the loads on these structures. A series of physical model tests were carried out to examine the order of wave pressure reduction for different height of the breakwater related to the local water depth. One has to be careful, when the crest of the breakwater is immersed with about 17% of the water depth, during which, water jetting effect is found to increases the pressures. Modification factor in association with Goda's formula is proposed to estimate the shoreward pressures on the seawall in the presence of the offshore breakwater. Statistical analysis is carried out on the measured pressure data and the wave pressures for 2% probability of exceedence for different breakwater heights w.r.t. the water depth are given in this paper.