4.1.7 Effect of rock bolts: when a rock bolt is installed at angle β from the normal to the failure plane, it increases the increase normal stress by Tcosβ and reduces the driving forces by Tsinβ (figure 7),  where T is the tension in the rock bolt. 

 

Figure 7: Geometry of slope with tension crack in upper slope and its interaction with rock bolt

Therefore, the expression for factor of safety of the slope becomes

 

FOS =