# 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
#### 3.3.3 Effects of Grout Mechanical Characteristics on the Axial Performance of FGRBSs  
In general, grout acts as an interface between the retaining system, such as rock and cable bolts, and surrounding rocks with their loading transfer abilities. As a result, the performance of FGRBSs heavily depends on the quality and mechanical behaviours of the grouts. Moreover, these behaviours are controlled by some significant parameters, such as W/G ratios, CT, additives, proper mixing of grout components, and the type of grouts. As a result, certain researchers focused on investigating the impact of the strength properties of grouts [10; 38; 43; 58; 66; 78; 79; 80]. For instance, [PERSON], [PERSON] [58] found that the bearing capacity of the fully grouted cable bolting system increased by 50 to 70% in lower W/G ratios under 40%. This is due to the fact that lower (W/G) ratios presented higher mechanical characteristics including UCS and Young's modulus. [PERSON], [PERSON] [66] performed a pull-out test to find the effects of different types of cementitious grouts on grouted anchors. By comparing the results, they found that the bond stiffness and essentially interfacial BS depended on the mechanical properties of the grout. It was concluded that the bond stiffness values in threaded bars are higher than those of stranded cables. [PERSON], [PERSON] [38] investigated the effect of grout properties on the axial bearing capacity of FGRBSs. They found that the W/G ratio should not be of more than 40% (wt). The lowest values of UCS and shear strength of grout (\(\tau_{g}\)) were achieved in grout mixtures with higher ratios of W/G. [PERSON] et al. (2014) proposed methods for preparing and testing different properties of grout and resins such as, UCS, Elastic modulus (E), \(\tau_{g}\), creep, and rheological properties. [PERSON], [PERSON] [71] reported the water content as an influential factor affecting the critical embedment length. [PERSON], [PERSON] [81] investigated the mechanical behaviour of two types of grouts mainly used in Australia, Jennmar Bottom-Up 100 (BU-100), and Orica Stratabinder HS. For this purpose, a series of compression tests were conducted on 50 mm cube samples, which had been cured over a period of 1 to 28 days. The results show that the UCS of both grouts increased over curing time. The experimental creep testing results from samples cured for 42 days in the study conclude that there is no notable discrepancy in the creep behaviour of those grouts. [PERSON], [PERSON] [80] investigated the effects of W/G ratio on UCS of commercial grout products. The results show a 43% reduction in UCS once the W/G ratio increased from 28% to 42%. [PERSON] [83]  
Figure 12: (**a**) The relationship of Q under confining pressure (**a**) with pull-out load and (**b**) without pull-out load [77]. examined the influence of sample size and curing time on the strength characteristics of two commercially available encapsulation grouts. The findings reveal a progressive increase in UCS over time. Additionally, it was observed that the UCS of samples cast in smaller moulds is 1.5 times higher than that of larger samples. Interestingly, four point flexural test results indicate that bending resistance decreases with the CT. [PERSON], [PERSON] [91] reported a direct interrelationship between the grout's UCS and BS. An increase in the BS from 3.8 to 11.5 MPa is reported as the UCS of the grout increased from 30 MPa to 60 MPa. Experimental and field studies also showed that the optimum annulus thickness is in the range of 2-7 mm and delivers the best load transfer interaction. [PERSON] [86] investigated the bonding performance of FGRBSs encapsulated by different admixtures, including formulations incorporating silica fume, fly ash (FA), blast furnace slag, perlite, metakaolin, and other minerals. Pull-out samples, each measuring 150 mm in length, underwent testing at five different CTs ranging from 1 to 90 days.