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 activities. The possibility of excavating large underground tunnels in the seemingly “fragile” rocks in orogenic areas was considered as a national project for the underground storage of petroleum. One hundred and seventy sites in 57 areas were selected based on a comprehensive survey over the whole country. After a successful experiment with a test tunnel, 112 m long and 250 m 2 in cross-section area, excavated in Cretaceous granite, three sites in granites and pyroclastic rocks were selected for construction. The largest of these storage tunnels is 550 m in length and 20 × 30 m in cross-section. Before construction, a detailed survey of the subsurface geology was carried out, taking into consideration the structural geology, the mechanical properties of the rocks and the hydrogeology. It was concluded that even in active orogenic areas, there are many suitable sites for large underground excavations and that these can be detected by detailed, planned surveys.
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