Effect of Cable Quantity in FLAC3D on Rock Bolt Pull-out Simulation Results

In order to study the influence of the number of cables on the simulation results when the same length of the bolt is prepared, the bolt is created by using the Cable structure element in FLAC3D, and the simulation experiment is carried out under the same surrounding rock properties, mesh density and boundary conditions. The effect of the number of cables and the effect of grout stiffness was further explored. The results show that the recommendation to set the number of cables according to the development length in FLAC3D help manual is not reliable. When the same length of the bolt is divided into different numbers of cables, the simulation results are significantly different. When the length of a single cable is consistent with the length of the mesh or shorter than the mesh, the bolt can obtain a large pulling axial force. The ultimate pull-out force of the bolt can be determined according to the on-site pull-out test, and then a single cable length is set to be between 0.5 and 1 times the length of the grid in the numerical simulation to find a simulation scheme consistent with the field test. The change of grout stiffness has no significant effect on the peak force of the bolt axial force, but it will change the post-peak variation characteristics of the axial force.