The semi-circular breakwater is a new light gravity type of structure suitable for soft foundation. It is necessary to establish a reasonable calculation and analysis method for stability and failure mode of the semi-circular breakwater under combined loads. Stability analysis method of the semi-circular breakwater under combined loads is developed by combining load mode with finite element method of the large coastal structures on soft foundation. Meanwhile

sliding failure along the bottom of the base plate and rubble-mound foundation

and vertical bearing capacity failure of the soil foundation are considered. Furthermore

stability failure mode and failure envelopes of structural bearing capacity are obtained. Finally

the effects of amount of filling sand in caisson

the width of rubble-mound foundation

and the reinforcement depth of soil foundation on stability of the semi-circular breakwater are analyzed. The calculating results show that the sliding surface and foundation bearing capacity failure lines of the semi-circular breakwater under combined loading divide the whole V-H loads space into four regions

namely stable region

slide-only failure region

region where only foundation bearing capacity failure happens and region where both sliding failure and foundation bearing capacity failure happen. The foundation bearing capacity failure line obtained by load and displacement composite load mode is outside the failure line obtained by Swipe load mode. But for each load mode

change trends of foundation bearing capacity failure lines are almost consistent. It can be seen that safety factors of stability against sliding along the bottom of caisson or rubble-mound foundation both increase with the height of filling sand in caisson

but safety factors of foundation bearing capacity decrease. Meanwhile

safety factors of foundation bearing capacity obviously increase with the increase of width of rubble-mound foundation or reinforcement depth of foundation.