EVALUATION OF STABILITY OF CAISSON-TYPE BREAKWATERS WITH REINFORCED EMBANKMENT UNDER TSUNAMI ATTACKS

Abstract

 In the present study, in order to establish a stability evaluation method of a caisson-type breakwater against a tsunami, mechanical behaviors of the laterally loaded caisson and the reinforced embankment behind the caisson were discussed on the basis of the results in numerical simulations using the two-dimensional discrete element method. Two types of a tsunami bore and a tsunami overflow were assumed by changing the points of force. As a result, the horizontal resistance in the case of using the reinforced embankment was up to 3 times as great as that without the reinforced embankment. Moreover, it was revealed that the behavior of the caisson and the earth pressure distribution behind the caisson were entirely different under two external force conditions. Judging from the analytical results, the contact pressure beneath the caisson and the stress on the base of the reinforced embankment were postulated as a triangle distribution. The load distributions were given as external forces and a circular slip analysis was carried out. By the circular slip analysis, the bearing capacity can be evaluated under the condition of the tsunami overflow. The moment equilibrium was considered for the condition of the tsunami overflow dealing a trapezoidal distribution as the earth pressure behind the caisson. From the comparison with the DEM result, it was revealed that the stability was adequately evaluated by the moment equilibrium.