## 1 Introduction  
In civil and mining engineering, ensuring the safety of underground and surface structures, as well as workers, is paramount. To prevent catastrophic disasters, support systems are crucial to help the ground bear and distribute loads. In fact, before excavation, the rock mass is in equilibrium, with stress forces acting downward. However, these forces deviate after excavation and go towards a new pathway. This is where the reinforcement elements will play a vital role in transferring the loads from unstable zones to stable ones. For decades, rock reinforcement elements like rock bolts (typically less than 3 m), cable bolts (typically 3-10 m), and ground anchors (exceeding 10 m), have been used to prevent or control rock falls caused by underground excavations and surface slope instability [1; 2; 3; 4]. A typical rock bolting system includes four main parts: surrounding rock mass, bolt, and internal and external fixatures. The internal fixture is typically a cementitious grout, resin, or friction created by the interaction between the bolt and the surrounding rock. The external fixtures are the face plate and the nut [5]. In general, rock bolts can be classified into three different categories [6]: (a) mechanically anchored bolts which are typically applied for temporary rock supports, such as a wedge or expansion-shell bolts; (b) frictional bolts, such as split-set and swellex bolts, which are generally employed as a temporary supports; and (c) grouted bolts, such as cemented grouted rebars, and hollow-core self-drilling bolts, which are considered for application in both temporary and permanent supports. The selection of the most suitable rock bolt type hinges on the specific application and geological context [1]. Among all different rock bolting types, fully grouted rock bolts often emerge as a highly versatile and widely employed option due to several key advantages. Their versatility allows them to be used in weak or fractured rock formations, highly tectonic zones, and even in corrosive environments [7]. This system consists of a ribbed/smooth steel/composite bolt, a face plate, a nut, and grout/resin [8]. The performance of rock bolting systems under axial load transfer conditions is evaluated by conducting experimental studies, including laboratory or in-situ pull-out (PL) tests. These tests involve applying tensile loads to the bolt head and measuring the resulting displacement or deformation [2; 3; 4]. One of the most significant results of conducting these pull-out tests is determining the axial load-bearing capacity of the rock bolting system, which equals the maximum loads of the pull-out (MLP) tests. Also, some other vital parameters, including yield load, stiffness, the elasticity modulus of bolt-grout (B-G), the shearing bond strength (\(\tau\)) of bolt-grout-rock (B-G-R), and the failure modes of the B-G-R, can be studied by applying PL tests. The significance of load behaviour on rock bolt performance has been a significant focus of research for decades, with studies using pull-out tests [2; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. For instance, [PERSON] et al. [17] conducted pull-out tests to investigate how different cementitious grouts affect anchored bolts' performance. They concluded that the stiffness of the bond between the grout and the bolt, as well as the overall bond strength, is influenced by the mechanical properties of the grout itself. [PERSON] et al. [6] investigated the effect of some influential mechanical characterisations of grout, including various ranges of curing time (CT), different ratios of water-to-cementitious grout (W/G), and multiple values of uniaxial compressive strength (UCS) on the axial load bearing capacity of fully grouted rock bolting systems, using different PL tests. In another research, [PERSON] et al. [5] investigated the effect of different fully grouted steel rebar shapes on the values of MPL. After conducting the required PL tests, [PERSON] et al.