PROBLEM TO BE SOLVED: To largely reduce construction cost, by reducing a scale of a ground improvement of a submerged bank part, in an artificial shoal or a dry beach of using dredge soil as an infilling material.SOLUTION: A reinforcement soil layer B is provided on the shore side of a submerged bank A, and the submerged bank A is constituted of submerged bank parts a1 and a2 of upper-lower two stages, and these submerged bank parts a1 and a2 are provided so that a part of a bottom surface of the submerged bank part a1 of the upper stage contacts with a top end surface of the submerged bank part a2 of the lower stage, and the reinforcement soil layer B is constituted of reinforcement soil smaller than unit volume mass in water of a component of a submerged bank A in unit volume mass in the water, and becoming 40 kN/mor more in uniaxial compressive strength after 28-day curing, and is provided by contacting with a residual part and a side surface of the bottom surface of the submerged bank part a1 of the upper stage and a side surface of the submerged bank part a2 of the lower stage.SELECTED DRAWING: Figure 1【課題】中詰材として浚渫土を用いる人工浅場又は干潟であって、潜堤部分の地盤改良の規模を小さくすることにより、施工コストを大幅に低減する。【解決手段】潜堤Ａの岸側に補強土層Ｂが設けられ、潜堤Ａが上下２段の潜堤部ａ1,ａ2で構成されるとともに、これら潜堤部ａ1,ａ2は、上段の潜堤部ａ1の底面の一部が下段の潜堤部ａ2の天端面に接するように設けられ、補強土層Ｂは、水中での単位体積質量が潜堤Ａの構成材の水中での単位体積質量よりも小さく、且つ２８日養生後の一軸圧縮強さが４０ｋＮ／ｍ２以上となる補強土で構成されるとともに、上段の潜堤部ａ1の底面の残部及び側面と、下段の潜堤部ａ2の側面に接して設けられる。【選択図】図１
