Micromechanical model for simulating load transfer behavior and damage evolution for fully grouted rockbolt under axial loads

In the present paper the problems of the nonlinear debonding of anchorage interface, the strain-hardening and rupture of rockbolt, and the progressive damage of heterogeneous rock for the fully grouted rockbolt under axial loads are studied. A micromechanical numerical model is developed and implemented into the finite difference programme, to analyze the load transfer mechanism and damage evolution by introducing the bi-exponential shear slip model of interface, bilinear strain-hardening model of rockbolt and elastic damage model of rock. The close agreement between the simulation results of the proposed model and the theoretical and experimental data validates the model's capability for accurately characterizing the pull-out behavior of the grouted rockbolt. Failure type strongly depends on the strength of rock and anchorage interface, as well as the anchorage length. In particular, when rock strength is low, strain energy is predominantly dissipated through rock damage, leading to the interface failing to fully mobilize its load transfer effect, especially at a relatively long anchorage length. Moreover, the excessive interfacial adhesion performance causes a large range of serious damage in rock near the interface and leads to peak pull-out load even lower than the rockbolt with poor interfacial bonding properties. Finally, the critical anchorage length is investigated and the load transfer mechanism of the fully grouted rockbolt is clarified by comparing the case with or without rock damage. It is therefore very useful of the developed micromechanical model, since it provides an essential understanding of the load transferring capacity and failure type of the fully grouted rockbolt, especially under rock damage.