Jointing structure characterization for the preselected area of China's deep geological disposal of high-level radioactive waste

Jointing structure is considered in most of the rock mass classification systems and it takes a great weight in those rock mass classification systems. However, the rock mass classification systems take different parameters for characterizing jointing structure and most rock engineering is carried out using various descriptions. A general jointing structure characterization method is of great significance for site selection, repository design and performance assessment for high-level radioactive waste repository. This paper concentrates on a common approach to jointing structure characterization and the results for Beishan area, Gansu province, the preselected area of China's deep geological disposal of high-level radioactive waste. A synthesis index, JSR (Jointing Structure Rating), is developed to characterize the jointing structure of rock mass. The main principle in the development of JSR is concentrated on the cleavage of rock mass by joints regardless of this cleavage may reduce the strength or increase the permeability of rock masses. JSR is the combination of joint density, joint size and joint set number. JSR may serve as a general index which can be used to evaluate both the block size of rock mass and the connectivity of joints network. The main joints characterization such as orientation, joint set number, mean trace length and midpoint density is evaluated after detailed field joint survey in Beishan area. Based on JSR and joints statistical description, jointing structure classification for the sections of Beishan area is given. The results provide a global vision of the jointing structure in Beishan area and provide a basis for site selection and preliminary near-field performance assessment. (authors)