Longitudinal Deformation Profiles for Sequentially Supported Deep Tunnels in Strain-Softening Hoek–Brown Rock Mass

Numerical methods are commonly applied in tunneling design practice for the prediction of rock mass behavior during tunnel construction and for primary support dimensioning. Although the sequential excavation and primary support installation in phases is a complex three-dimensional problem, in practice it is usually approximated with plane strain simulations. For their correct application, the knowledge of the confinement level prior to the installation of the support is necessary and requires the construction of an accurate longitudinal deformation profile. This study presents a practical methodology for the estimation of the confinement level at the support installation position based on the execution and interpretation of a large number of plane strain, axisymmetric and 3D numerical simulations. All simulations incorporate sequential excavation and support cycles in confinement depended strain-softening Hoek–Brown rock mass. The results indicate the importance of the post-peak rock mass behavior and the influence of the installed support to the confinement level for both top-head and bench excavation and support stages.