# Axial Load Transfer Mechanism in Fully Grounded Rock Bolting System: A Systematic Review
## 3 Analysis and Results
### Influential Parameters on the Axial Behaviour of FGRBSs
#### 3.3.2 Effects of Boundary Conditions and Rock Mass on the Axial Performance of FGRBSs  
The strength of the rock mass can heavily affect the failure mechanism of the FGRBSs. In the soft medium (rocks), the primary failures tend to occur in the R-G interface. Conversely, strong rock sees failures predominantly in the B-G interface. Along with the pressure of internal confinement, the critical role of in-situ stress, the pressure exerted by the surrounding rock has also been thoroughly acknowledged [13; 31; 41; 48]. Indeed, relaxation of in-situ stress can lead to a substantial decrease in the anchoring effectiveness of the FGRBS, particularly at the rock-grout interface. It is noteworthy to mention that,  
Figure 8: General applied load–global slip curves [69] (Copyright was given by ScienceDirect). Figure 10: (**left**) Critical EL vs. UCS and W/G ratios; (**right**) relationship between BS and EL [71]. Figure 9: Loaded end slip of long reinforcement in concrete [70]. (Copyright was given by ScienceDirect)). in the very soft rocks, the axial stress along the bolt decreases due to the uniform distribution of shear stress along the bolt [47]. The radial dilation is induced by the axial slip of deformed rock bolts. However, the extent of dilational failure can be limited by the confining stress applied to the rock mass. Moreover, a higher normal stiffness of the rock mass serves to further restrict the incidence of dilation. Unlike soft rocks or intensively jointed and cracked hard rocks, in hard rocks without effective joints, dilation may increase the radial confining stress, resulting in the high bond capacity of the fully grouted rock bolt. [PERSON] [74] suggested two types of cracks: cone-shaped cracks, and longitudinal splitting cracks, which resulted in debonding during pull-out of steel rebar bolts inside the concrete. The development cracking pattern depended on surrounding concrete and the rebar geometry. [PERSON], [PERSON] [75] studied the effect of concrete compressive strength and rock mass integrity on performance of anchored rock bolts. They concluded that the failure modes of the joint rock are influenced by the rock mass integrity (K\({}_{\text{v}}\)), which can be categorised as follows: (a) structural failure with longitudinal cracks; (b) joint surface failure with rapid crack development around the prefabricated joints, resulting in joint surface failure, and (c) disintegrate failure with developing cracks near the joint surface, resulting disintegrated failure of joint rock (Figure 11). Three modes of boundary conditions can be applied in laboratory pull-out tests, including constant normal stiffness (CNS), constant normal load (CNL), and no boundary conditions. Constant radial stiffness can better reflect the actual field conditions because shear dilation is inhibited by surrounding rock mass [58]. [PERSON], [PERSON] [58] studied the influence of radial stiffness on the axial and shear behaviour of cable bolts by conducting a series of experimental split-pipe tests using various materials, including PVC, aluminium, and steel pipes. Their findings suggested a correlation between radial stiffness and failure mechanisms, with higher stiffness leading to distinct failure modes and ultimately, a greater axial load-bearing capacity. [PERSON], [PERSON] [56] carried out a series of pull-out tests under constant radial confining stress using modified triaxial Hoek cell to quantify the influence of confining pressure arising from frictional dilation. The confining pressure ranged from 1.3 to 7.5 MPa. The results reveal that, at lower confining pressures, cracks fully develop on the outer surface of the specimens, indicating slip accompanied by dilation. [PERSON] et al. [54] observed that radial fractures became more prominent at lower confining pressures. [PERSON], [PERSON] [60] reported similar trends, noting that dilational failure is the dominant mode at low normal stresses (0.5 MPa). However, as the normal stress increases to 2 MPa, shear-off failure becomes the primary mechanism.