When we adopt so-called CAES (Compressed Air Energy Storage system; a system of gas turbine power generator with the combination of compressed air storage in rock caverns) for leveling the electric load in Japan, the storage caverns are required to be unlined for reducing the construction cost. From this point a series of preliminary investigations were carried out on the geotechnical subjects concerning CAES with using unlined caverns in a sedimentary rock site near the sea in Japan. Among the subjects the prevention of the air leakage from the unlined caverns was a matter of great importance. Therefore this paper shows the results of the field study on the characteristics concerning air tightness of unlined storage caverns in a sedimentary rock test site near the sea. In the field a 600-meter deep borehole in 76mm-diameter was drilled and the hydrogeological characteristics of the sedimentary rock were surveyed. A new probe was developed and applied to the borehole test of the air tightness of the submerged rock as well as the air infiltration into surrounding rock. The results of air and water injection tests in the borehole confirm the assumption that unlined caverns in sedimentary rock has enough air tightness for CAES.
Leveling the electric load is a major issue of electric power suppliers in Japan. Among several proposals, so-called CAES (Compressed Air Energy Storage system; a system of gas turbine power generator with the combination of compressed air storage in rock caverns) will be an effective choice as a middle-sized storage system. If the storage caverns can be unlined and the air leakage can be prevented by the surrounding underground water (Figure 1), we can reduce the cost of construction of the storage caverns and increase the feasibility of the CAES in Japan.