PURPOSE:To preserve the natural view, and maintain the safety of a road by excavating a mountain slope to obtain a flat surface in conformity with a road shape, building an artificial foundation of circular arc form striding over the flat surface from a mountain top side to a valley side, and filling the upper surface of the foundation. CONSTITUTION:At a mountainous area and a sloped ground, a slope A is excavated to obtain a flat surface B in conformity with a road shape, and an artificial foundation 3 of circular arc form is constructed, striding over the flat surface B from the end of a mountain top side to the end of a valley side bottom. In addition, sediment retainers 4 and 4 are provided in a staggered form on the top of the artificial ground 6, and banking 6 is applied thereon for restoring an original mountainous slope. In this case, the flat surface B is divided into a mountain side surface B1 and a valley side surface B2 located lower via stepped portions, and vent pipes 5 passing through the foundation 3 and banking 6 are laid at suitable intervals.
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