Categorization of discontinuities for conceptual description of rock hosting repositories for hazardous waste

The weaknesses in a rock mass are discontinuities that determine its hydraulic and strength properties and have a major influence on the decision as to whether a proposed site for a repository for highly radioactive waste can be accepted or not and on the selection of a suitable repository design. Classification of discontinuities is needed both for general conceptual description of the constitution of a rock mass and for having a basis for defining relevant rock structure models for numerical calculations. The ultimate goal of the work described is to outline a classification scheme for the various types of discontinuities. The present paper gives a basis for this by proposing a general categorization scheme of discontinuities ranging from large fracture zones (first- and second-order), to minor fracture zones (third-order) and discrete fractures of various persistence, water-bearing capacity and strength (fourth to seventh order). The geometry and general performance of the respective category are defined, while specific physical properties cannot be ascribed to them because of the variation in origin and nature.