| 摘要 |
PROBLEM TO BE SOLVED: To provide the structure of a drain hole, to which various kinds of drain pipes having different outside diameters can be used. SOLUTION: In the structure of the drain hole 1 penetrated to a retaining wall 3 or a block 4 constituting the wall 3, at least three or more of peripheral wall surfaces 2 are bent and connected and formed continuously in order to shrink the diameter of the drain hole 1 by stages towards the surface 6 side while the whole peripheral wall surfaces 2 or the peripheral wall surfaces 2 on at least the surface 6 side and the rear 7 side are formed in a gradually shrunk shape towards the surface 6 side while making the degrees of each diameter shrinkage different. COPYRIGHT: (C)2004,JPO&NCIPI
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