A bank (12) is formed into a trapezoid cross-sectional shape by an embankment, in order to provide a seawall (10) having sufficient erosion resistance to overflow caused by a tsunami, and whereby the time until the seawall is destroyed or collapses even if the tsunami has overflowed the seawall is increased, thereby reducing the effects of natural disasters. A concrete wall section (14) is formed along a slope (18A) in the bank (12), said slope facing the water side (ocean side, river side). All of the top (16) and land-side slope (18B) of the bank (12), except the concrete wall section (14), is covered in a reinforcing layer (20) comprising crushed/compaction-rolled soil. The reinforcing layer (20) comprising crushed/compaction-rolled soil is provided by spreading, leveling, compaction rolling, and curing embankment soil having a variety of particle diameters and produced by an initial solidification soil being crushed to no more than a prescribed particle diameter, said initial solidification soil comprising a solidification material added to sedimentary gravel that is then agitated, mixed, and cured, and exhibiting a prescribed strength.
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