The Effect of Not Fully Grouted Rock Bolts on the Performance of Rock Mass

According to the characteristics of rock bolts in mining engineering, a mechanical model for not fully grouted rock bolt is presented to obtain the expression of shear displacement, the axial force and the shear stress along the anchor section. On these bases, the effect of the length of anchor section on the performance of rock mass and the effect of the axial force at the free end of the bolt on the performance of rock mass are analyzed by COMSOL Multiphysics. According to the results of numerical simulations, there are some conclusions as following: (1) a moderate length of anchor section, such as the length of 1.0 m similar to 1.4 m, is favorable in mining supporting design, which can make sure grout and rock in coupled state and reduce the construction cost; (2) the favorable distance between the rock bolts is from 0.9 m to 1.3 m; (3) more rock bolts should be installed if the rock mass has larger deformation, which also can make sure grout and rock in coupled state. Conversely, less rock bolts should be installed if the rock mass has smaller deformation, which also can reduce the construction cost.