Stability of dual circular tunnels in a rock mass subjected to surcharge loading

This paper investigates the stability of dual circular tunnels in a rock mass subjected to surcharge loading using adaptive finite element limit analysis (AFELA). The tunnels are modelled under plain-strain conditions, and the rock mass is assumed to be a homogeneous and isotropic material obeying the Hoek-Brown failure criterion. For the studied problem, numerical kinematic and static approaches are employed to calculate the rigorous upper and lower bounds of the stability number N, which has been bracketed within +/- 5% from above and below. The calculated results are presented in the form of dimensionless stability charts, and the typical failure mechanisms are discussed through parametric studies of the problem variables using the visualized results of AFELA.