PURPOSE: To expand a stormwater-permeable area by providing a stormwater flow hole at the bottom of the side wall of a side drain, a stormwater-permeable layer comprising superposed layers of spherical molded items connected to the hole, and a sand filtration layer over the stormwater-permeable layer.
CONSTITUTION: A concrete layer 5, as a sand filtration layer, is provided between a stormwater-permeable layer 3 and an underground layer 12 to prevent sand to fall down onto the layer 3 from the layer 12. The stormwater flowing in a side drain 2 flows through storm water flow holes 25 into the layer 3 and then smoothly flows along the arcuate-upstanding surface of a wire-mesh cage 4 and hence deposite of sand, which causes clogging in the layer 3, is avoided. Since the layer 3 is composed of spherical molded items 30, resistance to the flow of stormwater is small and stormwater evenly penetrates through the layer 3. As a result, stormwater can be passed through the underground over a wide area.
YAMAGUCHI JUNKO
YANAGAWA YASUSHI
SUGA SHINICHIRO
MATSUKAZE YUUJI
