Abstract: In general, the properties and parameters of fractured rock mass are changed with the increase of rock mass size. But when the size increases to a critical state, the properties and parameters of fractured rock mass remain unchanged. The critical size is called the representative elementary volume (REV) of fractured rock mass. In this paper, based on an underground oil project in China and the method to determine REV size in radial flow configuration, the REV size for permeability and the permeability coefficient of fractured rock mass in the area of underground oil depot cavern are investigated, and the REV size is 37.5 m for radial flow configuration, which is 1.3 times of the trace length. The influences of trace length, spacing and gap length on the REV size and permeability coefficient are investigated as well. The REV size and permeability coefficient are influenced by the trace length and spacing, and the REV size is not influenced by the gap length. REV sizes and permeability coefficients under the conditions of radial and unidirectional flow configurations are calculated, and the REV size and permeability coefficient obtained in radial flow configuration are closer to the actual project and the calculation method is more convenient.

Key words: fractured rock mass, permeable property, representative elementary volume, radial flow configuration