Identification of homogeneous region boundaries of fractured rock masses in candidate sites for Chinese HLW repository

Identification of homogeneous region boundaries in a fractured rock mass is the basis of statistics and modeling of discontinuities. In engineering practice, an objective division can be obtained by adopting the major influential factors as indicators and the optimal approach as a tool. For discontinuities in Beishan, a main candidate site for Chinese high-level radioactive waste (HLW) repository, pretreatment techniques (e.g., sampling window truncation, sampling bias correction and block-net variation correction) were used to deal with field data. Programming was then applied to realize homogeneous region division via several methods (e.g., the improved Miller’s method, Mahtab and Yegulalp’s method, and correlation coefficient method). This study preliminarily examined these methods’ distinguishing capability, applicability, and limitations. Results showed that the applicability of the correlation coefficient method as well as the Mahtab and Yegulalp’s method was weak; the improved Miller’s method appeared most satisfactory, especially with a large-area strategy (34 blocks). Finally, two statistical homogeneous regions were obtained by applying the optimal approach to the Jijicao block. Findings can offer guidance for subsequent research on discrete fracture network (DFN) modeling and seepage path simulation, which is important for the prediction and evaluation of radionuclide migration in rock masses.