A sand layer often empirically is utilized as a buffer material in the protection structure with high bending rigidity as like rock shed. However, the method for estimating the amount of the plastic bending deformation has not been established, when a large rock collides with the structure exceeding the elastic range. H shape steel beams were used for a protection structure on which a sand tank containing river sand was installed in this study. The series of impact experiment by free drop of steel weight as a model of rock fall were achieved under the various conditions. The applicable range of various bending displacement estimation methods was examined and concretely shown.
