To reduce the thickness of bottom slab by jointing the heads of a plurality of piles driven to the ground below the slab to the bottom slab of an underground tank and by supporting the weight of content and buoyancy due to underground water, etc., acting to the bottom slab of the tank by the piles.
For building an underground tank 1, a cylindrical underground continuous wall 3 is built underground at first, its inside is excavated to a predetermined depth, and the excavated bottom portion is handled as ground 4 for placing floor. Then, a plurality of piles 11 are driven to the ground 4, heads of piles 11 are jointed to the bottom slab 7 of the circular tank, the cylindrical side wall 5 is erected along the inner surface of the underground continuous wall 3, a roof 9 is built over the side wall 5 and the underground tank 1 is constructed. In this way, the weight of content acting to the bottom slab 7 of underground tank 1 and the buoyancy acting to the bottom slab 7 due to surrounding groundwater when the underground take 1 is empty can be both supported by the piles 11 and thus the thickness of the bottom slab 7 can be reduced. Also, instead of using piles 11, plate shaped walls of various shapes and arrangements may be provided.
HAYAKAWA YASUYUKI
SUZUKI KENICHI
FUKADA ATSUHIRO
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