PURPOSE:To construct a large scale LNG underground tank safely at a low cost by a method having the same content as that of a freezing method through utilization of freezing of a ground by means of the cold heat of LNG stored in a small scale LNG underground tank. CONSTITUTION:An underground tunnel in an annular shape in a horizontal direction is excavated in a plurality of rings in the outer periphery of the construction position of a large scale LNG underground tank 2 and a heat insulating material 6 and a membrane 7 are arranged as a lining on the inner surface of a structural body. Airtightness is ensured by using the membrane 7 to build a first stage small scale LNG underground tank 1. LNG is stored for a feed in the small scale LNG underground tank 1. After it is confirmed that the freeze region 8 of a ground occurring owing to a feed is developed to a degree at which no problem arises, the inner ground of the ring is excavated to build a non-freezing type large scale LNG underground tank 2.
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