On national energy storage projects, the underground oil storage projects are under construction at three sites in Japan. As to large-scale caverns excavated by NATM in deep, fresh and homogeneous rock masses, an attempt of rock classification and evaluation systems with an abbreviation “CHIKABI Classification System” was made. This classification system is composed mainly of “Rock Hardness” and “Joint Spacing”, with supplementary geological factors of “Weathering and/or Alteration degree”, “Joint plane conditions” and “Water seepage conditions”.
The design criteria of the caverns and their supporting measures were made based on the said classification and evaluation systems practically. In order to correlate the actual rock conditons with the rock evaluation results, in situ measurements of P-wave velocity have been carried out in the excavated caverns.
In this paper, a principal thought and practical applying conditons of the classification and evaluation systems and a part of the results are described.
