It has sufficient erosion resistance against overflow due to tsunami, and even if the tsunami overflows, it secures a long time until the seawall 10 breaks or collapses to reduce disasters. The cross section of the levee body 12 is formed in a trapezoidal shape by embankment. The concrete wall portion 14 is formed along a slope 18 / b A facing the water body side (sea side, river side) of the dam body 12. The whole area of the top end 16 and the land-side slope 18B excluding the concrete wall portion 14 of the dam body 12 is covered with a reinforcing layer 20 made of crushed and compacted soil. The reinforcing layer 20 made of crushed and compacted soil is produced by crushing the initial solidified soil that has developed a predetermined strength by adding a solidifying material to the sedimentary sand, stirring and mixing it, and curing it to a predetermined particle size or less. It has been prepared by laying, spreading, rolling, and curing embankments with various particle sizes.
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