The Development of Spectrum displacement for Seismic Design of Urban Metro Tunnels with Circular CrossSections in Alluvial Soil based on SSI

Buried structures such as tunnels, depending on geometric shape, burial depth and various geotechnical and seismic parameters, exhibit different behavior in the event of an earthquake. Tunnels with circular cross-sections are now widely used in the field of transport. One of its most prominent uses is the urban metro that is created using tunnel drilling machines. The behavior of these structures against earthquakes at the time of operation is something that must be considered when designing. The tunnel structure is more sensitive to the ground's displacement than other seismic parameters, on the other hand, the effect of the vertical component of the earthquake on the tunnel structure is less in the far field. Therefore, vertical displacement of the tunnel is less important than horizontal displacement. In this study, variations in depth of placement, diameter and thickness of the tunnel lining and soil properties were performed and in this regard, the vibrating frequency of the soil and tunnel mass has been calculated. In the following, the maximum horizontal displacement component of the tunnel crown was calculated under eleven important and well-known earthquake record. Also, the relationship between the maximum horizontal component of the tunnel crown displacement and the frequency of soil and tunnel mass has led to the production of spectrum of the displacement. Using Plaxis and Ansys finite element softwares, a study was conducted on an urban metro tunnel with horizontal components of earthquake records similar to alluvial soils of the site. The results indicate that the envelope diagram on the horizontal displacement of the tunnel crown is changed in a nonlinear function during the investigating period. Also, the effect of changing the depth of placement and the thickness of the lining and the diameter of the tunnel on reducing the horizontal displacement of the tunnel's crown have been studied.