## 3 Results
### Induced Stresses
#### 3.1.5 Effect of Rock-Mass Type on the Performance of Fully Grounded Rock Bolt  
Several parameters affect the rock-mass conditions, including the strength of the intact rock, joints frequency, groundwater inflow, condition, and orientation of joints, with respect to excavation [2; 5; 7]. The core objective of rock reinforcement is to make greater use of inherent rock-mass strength and deformation characteristics to enable the rock media to support itself by improving the mechanical properties, provide rock confinement, and stabilization of jointed rock masses. The load that acts on the support system is referred to as the support pressure, and the support pressure depends on rock-mass quality and excavation span [5; 57]. Rock-bolt performance is restricted by the effectiveness of the load-transfer mechanism. This load-transfer mechanism is determined by the anchorage performance of the rock bolt through a rock-bolt anchor-pull test [58]. Rock-mass strength, which depends on the rock-mass quality, is one of the factors that can affect the load-transfer characteristics in fully grouted rock bolts. The effect of the rock-mass type on fully grouted rock-bolt behavior was investigated by performing pull-out tests on the moderate rock, soft rock, and weathered rock. Test results in term of the median pull-out strength and displacement are shown in Figure 10. Rock-mass quality shows a direct relation with rock-bolt pull-out strength and an inverse relation with pull-out displacement.  
Equation (12) [2] was used for the calculation of support load, and the results were compared with the median pull-out strength results (Figure 10), as shown in Figure 11.  
\[P=\frac{100-RMR_{89}}{100}\times\gamma\times B \tag{12}\]  
where \(B\) = the tunnel span (m); \(\gamma\) = the rock density (kg/m\({}^{3}\)).  
Figure 9: Composite support reaction lines. (**a**) Case 1: different support elements installed at the same time after tunnel excavation. (**b**) Case 2: different support elements installed at different times after tunnel excavation [56].  
Figure 11: Comparison of empirically calculated rock load with pull-out strength results in three different rock-mass types (**a**) moderate rock, (**b**) soft rock, and (**c**) weathered rock.  
Figure 10: Rock-mass quality effect in rock-bolt pull-out tests (**a**) in term of pullout strength and (**b**) in term of pullout displacement.  
Groundwater factor is included in empirical rock-mass classification systems; however, in water-bearing rock conditions, pull-out resistance of fully grouted rock bolt is highly dependent on groundwater inflow. The effect of groundwater inflow into the borehole was investigated by carrying out the pull-out tests. For soft rock and weathered rock with a groundwater inflow of 0\(\sim\)3.78 L/min, rock bolts with a length of 4 m were tested. The test sections were divided into two groups, one section having slight leakage of groundwater, and the other having significant leakage of groundwater, based on the inflow rate of 1.0 L/min; the results are shown in Figures 12 and 13. In water-bearing rocks, results of fully grouted rock bolts were further compared with inflated steel-tube rock bolts (ISR) for both small and large water flow for 4 m long rock bolts.