Geotechnical evaluation of a conglomerate for compressed air energy storage: the influence of the sedimentary cycle and filling minerals in the rock matrix.

It is necessary for the rock mass that surrounds the excavated storage cavern to maintain its mechanical and hydrological properties in order to keep the stability and air tightness of the storage caverns of the operating compressed air energy storage (CAES) system. A case study for the CAES, which included drilling a borehole of 600 m in depth, was carried out on the Paleogene sedimentary rock that consisted mainly of conglomerate in northeast Kyushu, Japan. Elastic wave velocity corresponds to the sedimentary facies and the mineralogy in the rock matrix that are controlled by the sedimentary cycle. The mechanical properties can be inferred from physical properties such as elastic wave velocity. Hydrological properties such as permeability coefficient and pore water pressure are affected by the grain size distribution and the filling minerals in the rock matrix that are controlled by the sedimentary cycle. Carbonaceous shale and sandstone with abundant filling mineral (calcite), which are distributed at the top of the sedimentary cycle, are inferred to be impervious. It is assumed that the groundwater flow is divided into two zones based on the vertical change of pore water pressure and one of these zones overlies the impervious layers and the other underlies the impervious layers. Finally we concluded that sedimentological and mineralogical studies were required to evaluate the mechanical and hydrological properties of stratified sedimentary rocks. pose a procedure for the geotechnical evaluation of sedimentary rocks that surround the CAES cavern.