## 1 Introduction  
In rock engineering design, the rock mass is considered as a complex natural geological building material and during tunnel construction, ground behavior is dependent on the ground condition and tunnel-related features [1]. The reason for the overall difficulty of modelling rock masses for engineering design is that the physical or engineering properties of rock mass must be established. This natural geological material is generally discontinuous, anisotropic, non-homogeneous and non-elastic [2] and produces uncertainties in modelling a rock mass. Modelling a rock-mass in a precise way allows scholars to decrease the ambiguity related with its characterization and replicate its inherent spatial inconsistency and heterogeneities [3]. For the purposes of rock engineering design, eight modelling methods have been categorized, including pre-existing standard methods, analytical methods, basic and extended numerical methods, precedent type analysis, empirical classification, the basic system approach and the combined system approach [4]. An important fact in rock mechanics is that having inadequate information for engineering design of structure in rock is a way of life,which is why the empirical rock-mass classification approaches have been established and are still essential for the tunnel construction. The qualitative picture of rock masses through empirical classification systems and the succeeding correlation to design parameters has become one of the most challenging areas in rock mechanics. Since the first descriptive rock-mass classification system, rock load classification, was established in 1946 [5], numerous empirical systems have been suggested for rock masses with the consideration of a specific rock mass structure and purposes [6]. The empirical systems used in tunnels construction as design tool are summarized in Table 1. The rock load classification constituted the basis of modern rock classifications [7]. In their original form, the suitability of these rock mass classification systems, for the complex rock-mass conditions characterization is not always possible, which results in the development of new systems or the modification or extension of existing ones. Among the several empirical rock-mass classification systems developed so far, the _RMR_ (rock-mass rating) system established by [PERSON] [8] and the Norwegian Geotechnical Institute (_NGI_) tunneling quality index (Q) system developed by [PERSON] and his co-researchers [9] are internationally accepted systems and are extensively used in tunneling. Additionally, these systems are also considered as the origin for launching other systems for the classification of rock-mass [7; 10; 11; 12]. The _RMR_ and \(Q\) systems are admitted currently as a compulsory adjunct for evaluating rock-mass environments for engineering purposes. The two main objectives of these classification systems are easier communication between different users and as a decision-making tool [20]. The later objective is the remarkable practice of classification systems in rock engineering. The _RMR_ system was suggested in 1973, as a jointed classification system for rock-mass [8]. This system was established on experience in underground projects in South Africa [21]. Afterwards, this system went through substantial variations. These variations are commonly due to ratings added or modified for ground-water, joint spacing and their condition, rock alterability, excavation method and stress-strain behavior. This system was numerously refined numerous times and main modifications in its characterization and structure were made in 1989 and 2014 [22; 23]. The major changes in the structure of \(Q\) system were made in 2002 [24]. This system was established on tunneling case records for hard and jointed rock masses [25]. It was initially developed for the grouping of rock masses for assessing the need for supports in tunnels and caverns. Using a set of tables, for the characterization of rock mass, along with footnotes, the rating for various parameters can be recognized.