Rock Mechanics and Rock Engineering: From the Past to the Future – Ulusay et al. (Eds) © 2016Taylor & Francis Group, London, ISBN 978-1-138-03265-1 Effect of shape and size of sampling window on the determination of average length, intensity and density of trace discontinuity A. Kamali & K. Shahriar Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran M. Sharifzadeh Department of Mining Engineering and Metallurgy Engineering, WASM, Curtin University, Australia A. Aalianvari Department of Mining Engineering, Faculty of engineering, University of Kashan, Kashan, Iran A. Esmaeilzadeh Department of Mining and Metallurgical Engineering, Urmia University ofTechnology, Urmia, Iran ABSTRACT: The fractures geometrical characteristics can be calculated by various sampling methods in 1 dimension (1D) & 2 dimensions (2D). The Discrete Fracture Network (DFN) simulation results show some of the equations are suitable for calculation of mean trace length and the difference between actual value and their values is less than 15%.Apparent density is dependent on scale, but the Mauldon’s estimators are independent of scale despite the variation in fracture length. For all joint sets, the difference of apparent areal intensity by samplings windows and circular estimator is less than 5% proportionate to actual value. A reduction of Fisher constant doesn’t have much effect on mean trace length of the fractures with length less than 1.5 m, but it results in a 21% difference for fractures with length longer than 1.5m. Variation of this parameter affects the density, too and the difference can be 5% to 10% depending on fracture length. But, variation in Fisher constant doesn’t have any effect on areal intensity for fractures with length less than 2 m. 1 INTRODUCTION Characterization of fractures has an important role in describing the rock mass. Seeing that the rock mass structure cannot be investigated directly in three dimensions, thus fractures’ characterization is nor- mally described on limited area (area sampling) or scanline (Zhang et al. 2010). Trace length, inten- sity and density are important and commonly-used characterizations. These characteristics for estimat- ing the elastic properties of the rock, porosity of fractures and rock mass description for determin- ing its hydraulic and mechanical behavior with usage in hydrogeology, oil recovery, evaluation of hydro- carbon flow, storage in fractured reservoir and rock engineering, rout length and connectivity of fractures in fluid flow are beneficial and important (Mauldon et al. 1999 a, b, Rohrbaugh 2002). The determina- tion of the three above characterizations is necessary for constructing and verifying of the Discrete Frac- ture Network (DFN) (Kulatilake 2003, Reeves et al. 2013, Lei 2014). The estimation of these charac- teristics in field encounters problems as censoring and different types of biases such as length and orientation. Above characterizations are estimated by scanline, window or areal and circular sampling meth- ods. Scanline sampling is a quick method for recording the fracture characterization, but it has size, trunca- tion and censoring biases (Zhang et al. 2010, Zeeb et al. 2013). There are various methods as regards the impor- tance and the main role of fracture trace length in the investigation of rock mass behavior and neces- sity of fracture size calculation. These methods are developed by Mauldon, Zhang & Einstein, Anderson & Dverstrop, Einstein & Baecher, Laslett and Pahl (Zhang et al. 2010, Ferrero et al. 2011). These methods use rectangle and circular windows for determining the fracture trace length. The developed equations by Mauldon, apparent density and apparent intensity equations proportionate to rectangle, circular windows and scanline are used to calculate of density and inten- sity, too (Zeeb et al. 2013, Mauldon et al. 2001). There has been no study the effect of Fisher constant (disper- sion of fractures pole around the mean pole) and the shape of window sampling considering four joint sets on the above three characterizations so far (to authors’ knowledge). 1073