Three-dimensional analysis of unlined tunnels in rock subjected to high horizontal stress

Abstract

An analysis of the stability of underground openings in weak rock is important to the design of the support requirements near the tunnel face. A detailed three-dimensional (3D) elastoplastic finite element study of face stability and the corresponding stresses around the face is conducted for a large-diameter tunnel in southern Ontario. The effect of the rock mass strength and high horizontal stresses on the tunnel deformation, stability, and distribution of tangential stresses at the tunnel circumference is investigated. To facilitate comparison with plane strain analysis, 3D results are presented for several cross sections across the tunnel. The effect of tunnel construction sequence on the predicted results is discussed.Key words: weak rock, tunnelling, horizontal stresses, three-dimensional, finite element, excavation, face stability, modeling.