ABSTRACT
Tunnelling in the underground produces open space larger than the final shape of a tunnel. Construction of the open space turns continuous condition of in situ rock masses into discontinuous state with respect to stress and flow. Due to the constructed open space, in situ stress will rotate along the perimeter of the tunnel and the rotated stress will concentrate near the crown or springline of the tunnel depending on the anisotropy of the in situ. This concentration of the stress will damage in situ rock mass in the form of the initiation and propagation of cracks, thus increased density and length of cracks near tunnel can be found (Cai et al. (2001)). In this paper, we will define this type of damage as structural damage.
