Uncertainty of fracture intensity measurement in discontinuous rock masses – A sampling window approach

Rocks typically consist of continuous intact rock and discontinuities. Fracture intensity, one of the geometrical properties, plays an important role in mechanical behaviors and hydraulic conductivity of discontinuous rock masses. However, discontinuous rock masses exhibit spatial variabilities in the fracture intensity due to the variation of geometric constituents. The accurate fracture intensity estimation is needed. The two-dimensional fracture intensity (P21) measurement is an efficient approach to predict the fracture intensity in a rock mass. This study proposes analytical solutions for the uncertainty in a fracture intensity measurement. The Poisson distribution is used formodeling the uncertainty ofa P21 measurement. To validate the analytical solutions, this paper uses a commercial discrete fracture network (DFN) code, along with an in-house DFN code, to simulate P21 measurement. The results showed that the uncertainty of a P21 measurement can be expressed by the size of sampling window, fracture diameter, and fracture intensity. An illustrative example is provided to illustrate the proposed method.