As part of establishing a national stockpile system for LP gas (liquefied petroleum gas), in Imabari City, Ehime Prefecture, a super-large cross-section cavity was excavated in bedrock 150m deep or deep underground, and a water-sealed bedrock storage tank was constructed that can contain LP gas at room temperature using the surrounding groundwater pressure. This is the first time in Japan to carry out water-sealing bedrock storage tank construction for LP gas, ensuring water-sealing functions, ensuring hollow stability, construction of a water-sealing supply system, and airtight testing, and the project has been completed for about 10 years.