Deformation and force analysis of inclined bolt under roadway roof separation

Full-length bonded bolt is widely used in roadway support. The structure of coal measure strata makes the roadway roof prone to separation. When the bolt is not perpendicular to the roof rock strata, it exerts not only an axial tensile effect, but also a lateral shear effect. Based on the shear slip theory and the mechanism of the pulling load on the bolt when the rock strata is in relative motion, the mechanical analysis model of the vertical bolt is established, and the relationship between axial displacement and axial tension is determined. Based on Winkle hypothesis, the mechanical analysis model of the inclined bolt is established and the formula for the bolt’s tangential displacement caused by separation layer is derived. According to Von Mises yield criterion, we can determine the maximum separation value, the axial shear slip range, the length of the failure section on the compression side, and the change value of local anchoring angle when the bolt yields. The model test data are used to compare the characteristics of the rock mass separation value against bolt axial force curves, demonstrating that the calculated value is in good agreement with the measured value. The results show that the proposed model has the capacity to predict the load evolution as well as the displacement evolution. The factors such as the location of separation layer, the separation value, and the bolt inclination angle are successfully accounted for in the analytical model.