Determination of Volumetric Joint Count Based on 3D Fracture Network and its Application in Engineering

Volumetric joint countis an important parameter to evaluate the development of fractures. It is a fundamental representative for the strength and permeability of rock masses. However, cannot be directly measured in field. In this study, an indirect method is applied for its estimation. The main procedures are as follows: firstly, the volumetric joint frequencyis assumed for th fracture set, and then a series of 3D stochastic discrete fracture networks (DFNs) are generated using the Monte Carlo method according to; secondly, a survey line is drawn perpendicular to the fracture set in the each fracture network generated, the fracture spacing is measured along the survey line, then the average fracture spacing and its variance coefficient are calculated from all the DFNs; thirdly, by repeating the above two steps for differentassumed, the relevant average fracture spacing and its variance coefficient are obtained, and two relation curves are built up between and the average fracture spacing (or its variance coefficient); fourth, the exactis estimated through this relation curve between and the average fracture spacing according to the exact fracture spacing measured in situ; finally,is calculated by summing the exactof all fracture sets up. In this study, this indirect method is applied in the rock masses of Xiaowan Hydropower Station. The result shows that the fracture spacing will reduce and its variation coefficient becomes stable asincreases.