## 1 Introduction  
After rock-load factor classifications came into being, many empirical systems were developed for tunnel-related design. Rock-mass rating (RMR) system [1; 2], rock-quality index (Q) system [3; 4; 5], and rock-mass index (RMi) [6; 7] are internationally accepted empirical systems for rock engineering. In tunneling, rock-mass classification systems classify the rock masses to aid tunnel design. In tunnel designs, the rock-mass quality as per the classification system, along with tunnel cross-sectional sizes, are used in the preliminary support design for safe and economic construction. Economy,simplicity, reliability, and the ability to withstand the tests of time are the factors behind the acceptance of using these empirical systems in tunnel design and construction. Fiber-reinforced shotcrete and rock-bolt support are the dominant preliminary support and reinforcement systems used in rock-tunnel construction [8; 9].  
In the RMR system, the rock-bolt design pattern was proposed for 20 mm fully grouted bolts and for tunnels with a span of 10 m [2]. After four decades of experience using the RMR system in tunneling, the rock-bolt length and spacing were extended for rock support as functions of tunnel span and rock-mass quality [10]. In Q systems, the 20 mm diameter rock-bolt spacing is a function of rock-mass quality, along with the presence of shotcrete (either sprayed or otherwise), and their length depends upon the tunnel span [11]. In RMi systems, rock-bolt spacing is a function of the ground quality and tunnel size, along with the presence of shotcrete (either sprayed or not), and the length of the rock bolt depends upon the tunnel span and block size [7].  
The main objective of rock reinforcement is to make greater use of the inherent rock-mass strength and the rocks' deformation characteristics to enable self-supporting rock media, and rock bolts are used for this purpose. This rock-mass reinforcement system comprises four principal components, which include the rock mass, reinforcing element, internal fixture, and external fixture [12]. The rock-mass classification system proposes a 20 mm diameter rock bolt length and spacing for a tunnel cross-section based on the rock-mass quality, although several factors have been studied in the past few decades to investigate the performance of rock bolts in different underground excavations.  
In this study, field tests were conducted as per ASTM (American Society for Testing and Materials) standards, to investigate the performance of fully grouted rock bolts under different rock-mass conditions defined by empirical classification systems. This study is the continuation and extension of our previous research, in which fully grouted rock bolts were used for the calculation of rock-mass quality for the extension of empirical classification systems [9; 13; 14]. Along with the field tests conducted for this work, much literature related to the fully grouted rock-bolts tests conducted either in a laboratory or on the field was also generated. Based on field tests and the literature, the different factors that affect the performance of bolts in different conditions are broadly categorized into five groups: bolt, fixture, rock mass, stress, and installation-related factors. Each group has several parameters that affect the performance of the rock bolts. Experimental results from the field and literature are combined, mainly focusing on the fully grouted rock bolts and an attempt is made to determine the interdependency of parameters aiming to design the efficient and economic rock-bolt patterns by using empirical classification systems.