Seismic Analysis of Rectangular Tunnels (Cut and Cover Method), Soil- Structure Interaction

One of tunneling methods is cut and cover method, in which the excavation start from the ground surface and deep in the ground, then a concrete box is made as a tunnel. Thus in this method, the cross section of the tunnel is not circular but rectangular. The aim of this paper is seismic analysis of rectangular tunnels. For a special accelerogram, tunnel geometry, depth of overburden and ground conditions, are the three main factors affecting the dynamic behavior of the tunnels. By numerical methods, and by assuming the plane strain condition, models of this type of tunnels were analyzed. According to the results, the maximum internal forces that are generated in the tunnel lining and the stress concentration are at the corners of the cross section of rectangular tunnel. In seismic mode, the internal forces of concrete lining are several times of static mode. In this situation, the ground surface settlement profiles are asymmetric and the settlement is greater than the static mode. In tunnels with large width, in 2D cases, if a column be placed in the middle of span, the ground settlement, bending moment and shear forces is decreased in comparison with 1 span tunnel with the same dimension