## 7 Conclusions and Recommendation  
Numerical techniques such as DFN modeling simulate the discontinuity of rock mass at scales ranging from each rock block to the scale involved in the entire engineering structure. DFN code like FracMan allow for direct two- and three-dimensional modeling of the physical properties of rock mass with definable fracture length, spacing, direction, etc., and therefore provides a much more representative alternative than the empirical characterizations and rock mass parameter estimation approaches through core logging. RQD has proved helpful in rock engineering as it gives a rough representation of the actual quality of rock masses. Through RQD measurement, the quality of the rock masses is assessed with simple tools with low operating costs, but inevitable limitations. Although these limitations have been addressed, RQD is still directly and indirectly (a parameter in some rock mass rating systems) used in many geotechnical engineering applications without correction. This paper studies the importance of the data characterization process for RQD determination through different measuring lengths and directions. In this way, based on the synthetic rock mass of 30 m, the influence of measuring length and sampling direction is given. The definition of REL and REV would depend on the variation in geotechnical domains. Note that the current analysis results apply to relatively homogeneous geotechnical domains, as both shear and fault zones should be treated separately. For the primary goal of the study of the scale effect, in this work, eight models were developed based on four classes of fracture density and two types of wells. RQD in each well of different measuring lengths was calculated using a method initially proposed by [PERSON] in 1963 to determine the scale effects in RQD with varying lengths ranging from 3 to 30 m. For intervals of each defined length (i.e. 3 m, 5 m, 10 m and 15 m), a maximum, a minimum, and an average value of the calculated RQD were recorded. The results indicate that, with the increase in the measuring interval, the variance in the calculated RQD of the synthetic fractured rock mass linearly decreases. The size of the REL of the fractured rock mass in terms of RQD was assumed to be ten times the recommended core run length by [PERSON] (1988) [9]. The estimated REL would represent the dimension at which the rock mass could be considered a continuum medium, and its properties would be defined using an equivalent continuum approach. When comparing all the models, the largest difference in the measured RQD extremum, which was calculated at an interval of 3 m, exists in the rock mass with the highest fracture intensity. The measured extremum difference is most sensitive to changes in core run length, followed by changes in fracture intensity, and then fracture orientation due to changes in the well drilling direction. Different thresholds of RQD determination were also used to study the scale effect. A comparison between rock mass scale and assumed threshold (10 cm vs. 20 cm vs. 30 cm) was made. The results show that greater REL occurs for longer thresholds. RQD represents a limited part of rock mass quality, and some inherent limitations result from its simple measuring manipulation. According to [PERSON] in 1988 [9], the calculation of the RQD should be based on the actual drilling-run length used in the field, but the laboratory core length is no more than 1.5 m. This methodology could serve as a reference for the quantification of RQD with a range and, thus, better predict the characteristics of the rock masses studied in engineering projects. This study proposed a method to define fracture sets by exclusively using linear discontinuity frequency data. Due to the constant length of the inserted well, higher frequency results in more fractures, whereas dispersity remains unchanged. In future studies, the spacing and persistence of fractures can be defined by constructing models with areal or volume density.