Numerical analysis of K0 to tunnels in rock masses exhibiting strain-softening behaviour (Case study in Sardasht dam tunnel, NW Iran)

ABSTRACT: This paper presents the results of numerical analysis of K0 (?h/?v) to tunnels excavated in rock masses obeying Hoek–Brown failure criterion with strain-softening post-failure behaviour. The numerical analysis was investigated in the Sardasht dam tunnel in north-west of Iran. The tunnel has a horseshoe cross-section through 4350 m in length with 3.9 in radius and will be used to transfer water to the powerhouse dam. Cretaceous slates with inter-beds of sandstone and phyllite crop out in whole of the tunnel route. In numerical analysis, a 2D finite element program with software Phase2 was utilized together with the convergence–confinement method. Considering that the tunnel is located at different depths, six sections of the tunnel have been selected and in each section, the K0 value is determined from the known relations and has been used in numerical analysis. The results of the evaluations show that in rocks exhibiting strain-softening behaviour, with reducing the amount of K0, the values of displacement and plastic zone around the tunnel increase but the style of deformation maintains uniform.