Modelling of fully grouted rock bolt based on enriched finite element method

Analysis of mechanical behaviour of rock mass reinforced by fully grouted rock bolt is introduced based on the enriched finite element method (EFEM). A solid element intersected by a rock bolt along any arbitrary direction is defined as ‘enriched’ element and it has additional degrees of freedom at each node for estimating displacements and stresses in bolt rod. Numerical procedures of EFEM are developed to form enriched stiffness matrix using constitutive relations of rock mass, properties of bolt rod and grout material and orientation of the bolt. Decoupling of rock bolt and elasto-plastic behaviour of rock mass has been incorporated into the EFEM procedures. Released displacement of rock mass prior to bolt installation has also been considered in the procedures to provide realistic solution. The results of this method are verified with an analytical pull-out test model. In addition, a numerical example of a bolted tunnel is provided to demonstrate the efficacy of the proposed method for practical applications.