| 摘要 |
PROBLEM TO BE SOLVED: To improve the water storage ratio against the capacity of a recess by forming a backing with a slope of an inclined face and a bottom face, and concurrently arranging block body packings and small-sized packings in the water storage space spread with an impervious sheet. SOLUTION: Block body packings 5 are stacked to the height of a water storage space 2 to form a first space with a high water storage ratio, and the periphery of the stacked block body packings 5 is covered with a bulkhead layer 6. Small-sized packings 7 are arranged and filled in the gap between the bulkhead layer 6 and a slope 3a. A shape along oblique sides can be formed by utilizing the small-sized packings 7, thus the land can be efficiently used. Since the installing and fixing work of an impervious sheet is conducted on the graded backing, it is simple and easy, additional sticking sheets are stuck from the inside of a water storage tank even if there are positions requiring additional sticking for execution, and high reliability against a water leak is achieved.
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