An experiment is conducted to clarify the mechanism of damage of gentle-slope sea dike constructed near the shoreline. Damage proceeds in the order, vanishing of sands on the slope, damage of foundation works, piping of backfilling stones, subsidence of armor units. The gentle-slope sea dike was the most easy to receive damage when it was founded in shoreline. It was considered to be one reason to cut the embedded depth of foundation works in shoreline by half of offshore side.
The scouring depth in front of foundation works was the largest when the sea dike was founded in offshore side. Though the precise solution to the effect of slope on scouring depth could not be obtained, the maximum value of it predominated in case of 1/3 slope.