ABSTRACT
Japan is located at the boundary between three continental and oceanic plates, and there is a great variety and complexity of geological features as a result of tectonic acitivities. In order to ensure both geological stability and engineering feasibility of excavating the large underground tunnels at a great depth in such “fragile” Japanese rocks, comprehensive geological studies was carried out over the whole country. As a result, three sites, two in Cretaceous granites and one in Miocene volcanics, were selected as suitable for the excavation of the underground caverns for storage of crude oil. After detailed site investigation in five years, construction in these three sites was successfully completed in 1994. Two sites have a total capacity of 1.75million kl of crude oil in ten caverns. The largest cavern completed is 550m in length and 20 × 30m in cross-section.
The important condition for the large excavation and opening in the orogenic areas that is required for storage of a huge amount of crude oil, liquefied petroleum gas, or compressed air energy is both geomechanical and hydrogeological stability of the rock-mass. Such stabilities are strongly dependent on behavior of the faults and fractures in the rock-mass.
