A "multi-phase" model for finite element analysis of traction forces in bolts used in the reinforcement of tunnel walls

This paper presents a mechanical model, called "multiphase model", designed to deal with ground reinforced by a network of regularly distributed linear inclusions. The main improvement of this model with respect to previous homogenization-based models for bolt-reinforced grounds lies in a better description of the mechanical interaction between the ground and the bolts, taken into account through the attribution of different kinematics for the ground and the reinforcements. The model has been implemented in a "research" version of the finite element code CESAR-LCPC, and used for the simulation of the construction of a tunnel under plane strain conditions. Results are compared with those obtained with two other approaches: the first one consists in treating the bolts as I D bar elements, while the other is a standard homogenization procedure. Results show that, while the deformation pattern around the tunnel is more or less the same regardless of the model used, the tensile forces in the bolts predicted by the multiphase model appear to be in much better agreement with those given by the calculation with bar elements.