A method to identify the connecting status of three-dimensional fractured rock masses based on two-dimensional geometric information

The hydraulic properties of three-dimensional (3-D) fractured rock masses are usually reduced to twodimensional (2-D) problems, which may lead to unreliable conclusions. This study provides a theoretical method to identify the connecting status (connected or disconnected) of 3-D isotropic fractured rock masses based on 2-D geometric information on cutting planes. The percolation threshold of 3-D fractured rock masses can be judged by the average number of intersections per fracture I. The relationship between I, number of fractures in per sampled area P-20 and trace length l are established. A connecting parameter P is defined to measure the average geometric information related to P-20 and l. When P < 0.88, the 3-D fractured rock masses is not permeable; and when P >= 0.88, the fractured rock masses are connected and permeable. Numerical experiments are conducted, and the results show that the developed theoretical formulae are valid. In addition, the estimation methods of P are also discussed based on l and number of fractures in per sampled length P10 or Rock Quality Designation (RQD).