| 摘要 |
PROBLEM TO BE SOLVED: To provide an underground water tank which is constructed by using a cylindrical shaft excavated by a cylindrical casing, ensures the watertightness and strength thereof by improving the quality of field-welding of a bottom slab, uses a steel of high corrosion resistance at a portion corresponding to a water tank of the cylindrical casing, and employs bottom-slab concrete in suitably adjusted quantity, for preventing floating of the water tank. SOLUTION: The cylindrical casing having a horizontal bracket on the lower internal periphery is employed, and the shaft is completed by the cylindrical casing, followed by welding the bottom slab to the bracket, to thereby improve the quality of field-welding. Further, by dividing the cylindrical casing into a portion forming the water tank and the lower excavating casing portion, the former is formed of a material of high corrosion resistance, and only the latter is formed of a general material, which leads to reduction of material costs. Further, the quantity of bottom slab concrete can be suitably adjusted depending on the individually different water tank.
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