Seismic Analysis of Shallow Tunnels in Soil Medium

Abstract

In both urban and national frameworks, tunnels form vital components of the transport and utility systems. They are being constructed in densely populated urban zones and metro cities at an expanding rate to promote rising space and passage requirements. Occurrence of any sort of seismic activity in that particular region may cause damage of these infrastructures. Hence, a careful consideration of the impacts of seismic loadings on the analysis and design of tunnels is required as a part of hazard evaluation. Different closed form analytical approaches exist, such as methods given by Wang and Penzien for seismic analysis of shallow tunnels. Ovaling deformations occur when seismic waves propagate perpendicular to the axis of tunnel and are therefore, designed for the transverse direction. In this paper, these two analytical solutions are used for the analysis of tunnel lining forces, constructed in soft to hard soil with various mechanical properties and constant shear strain. Seismic analysis was carried out by means of selecting eight unique types of soil, very soft clay to highly dense sand. The study indicates a relative error in both analytical methods. It was found that the variations in thrust and bending moment are dependent on the flexibility ratio, thus, it is proposed that the stress distribution is to be considered for analysis and design of tunnels’ lining. It is also seen that the induced circular stress in the tunnel liner is decreased with increasing soil stiffness.