A numerical model for fully grouted rock bolts considering the nonlinearities of the bolt and the bolt-grout interface

Fully grouted rock bolts are widely used in underground engineering, both the bolt and bolt-grout interface will exhibit apparent nonlinear behaviors when subjected to excessive load. Few of the existing studies simultaneously consider the nonlinear deformation characteristics both for the bolt itself and the bolt-grout interface. Therefore, according to the local deformation theory and finite difference method, a nonlinear numerical model for fully grouted rock bolts was developed. This numerical model can simulate the bolt's yielding and hardening behaviors as well as the bonding, softening, and decoupling behaviors of the bolt-grout interface, and its rationality was validated by comparisons between its predicted results and the experimental data and analytical solutions from published papers. Finally, this numerical model was used to simulate fully grouted rock bolts with or without faceplates installed in the field, and their mechanical performances and failure modes were investigated. Some conclusions were concluded: 1) The main failure mode of the rock bolt without a faceplate is the shear damage near the excavation surface, while the bolt pull-off adjacent to the excavation surface is its dominant failure mode after a faceplate is installed. 2) Ignoring the nonlinearities of the bolt and the bolt-grout interface overestimates its bearing capacity.