The function parameter X, C, T, m and the displacement vector orientations show some relationship between the modulus contrasts and the thickness of the weakness zones (Kim 2003). So, this paper suggests several qualitative clues for the effects of the

ABSTRACT: It is very difficult task to excavate a tunnel in poor and heterogeneous ground. Although with a good geological investigation, uncertainties due to the local rock mass structures will still remain. Especially for such conditions, a reliable prediction of the conditions ahead and outside the tunnel profile are of paramount importance for the choice of appropriate excavation and support methods. In this paper, we present the effects of the heterogeneity/anisotropy of the weakness zone on tunnel convergence. Three dimensional Finite Element simulations of different weakness zone properties, thickness, and orientation relative to the tunnel axis were carried out and the function parameters evaluated from the results. The results are compared to monitoring results from Alpine tunnels in heterogeneous/anisotropic rock. The good qualitative correlation between trends observed on site and numerical results gives hope that by a routine determination of the function parameters during excavation the prediction of rock mass conditions ahead of the tunnel face can be improved.