To evaluate the lateral resistance of single piles for dolphins under repeated loads and large deformations, lateral loading testes are carried out for model piles embedded in sandy soil in a laboratory. The model piles are made of high-tensile steel plates 2500 mm in length and 200 mm in width.
　The conclusions of this study are as follow:1) the test 1) The falling can be classified into two major types ; slipping type and tumbling type. A model to describe the both types of falling is proposed. The critical condition of the current velocity and the water level for falling can be evaluated by the model.
2) The horizontal force on the body can be evaluated as a drag force of which cofficient can be approximated as 1.1 from the experiments. The drag coffient varies
with the interval and direction of the feet.
3) The calculated values of the critical current velocity and water level for falling agree with the experimental values.
4) The critical wave runup height for the falling in front of breakwater is estimated as 50 cm.