ANALYTICAL SOLUTIONS FOR COMBINED BOLT-GROUTING AND LINING SUPPORTING IN VISCOELASTIC-PLASTIC ROCK MASS

The analytical solutions were derived for a deeply buried circular tunnel in a viscoelastic-plastic rock mass accounting for sequential excavation, bolt-grouting, and lining support. The solutions of stress and displacement as well as the radius of the plastic zone were presented for an enlargement excavation process with a time-dependent tunnel radius. The effect of longitudinal excavation was also considered. After reinforcement with bolt-grouting at any time, the reinforced rock mass was treated as homogeneous elastic-plastic material, with cylindrical orthogonal anisotropic characteristics to reflect the radial strengthening of the bolts in the elastic phase, as well as enhanced strength parameters to reflect the role of bolt-grouting in the plastic phase. The solutions for rock and liner in supporting stage were derived for the two cases, elastic and elasto-plastic, for reinforced rock. Moreover, the conditions were also given for emerging new plastic zones and the expression for plastic radius in reinforced rock. According to the solutions, stresses and displacements over time were analyzed at positions with different radii, and the influence of reinforcement and installation times of bolt-grouting reinforcement were illustrated. The solutions can be applied to the preliminary design of tunnel construction in similar conditions.