Analytical model of shear mechanical behaviour of bolted rock joints considering influence of normal stress on bolt guide rail effect

Rock bolts have been widely used in slopes as a reinforcement measure. Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts. Rock bolts under shear action exhibit the guide rail effect; that is, the rock mass slides along the rock bolt as if the rock bolt is a rail. The normal stress can inhibit the guide rail effect and reduce the axial force on bolts. However, this factor is not considered by the existing analysis models. Shear tests of bolted joints under different normal stresses were carried out in the laboratory. During the test, the axial force on each point monitored on the bolt was recorded by a strain gauge, and the attenuation trend of the strain was studied. An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints. The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage, and the estimated values agree well with the results of the direct shear tests in the laboratory. The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.