The role of shear wave velocity and non-linearity of soil in the seismic response of a coupled tunnel-soil-above ground building system

The presence of tunnels close to aboveground structures may modify the response of these structures, while the contrary is also true, the presence of aboveground structures may modify the dynamic response of tunnels. In this context, the dynamic properties of the soil through which the aboveground and underground structures are “connected” could play an important role. The paper reports dynamic FEM (Finite Element Method) analyses of a coupled tunnel-soil-above ground structure system (TSS system), which dier in regards to the soil shear wave velocity and in turns for the damping ratio, in order to investigate the role of these parameters in the full-coupled TSS system response. The analyses were performed using three dierent seismic inputs. Moreover, the soil non-linearity was taken into account adopting two dierent constitutive models: i) an equivalent linear visco-elastic model, characterized by degraded soil shear moduli and damping ratios, according to suggestions given by EC8 in 2003; and ii) a visco-elasto-plastic constitutive model, characterized by isotropic and kinematic hardening and a non-associated flow rule. The seismic response of the system was investigated in the time and frequency domains, in terms of: acceleration ratios; amplification ratios and response spectra; and bending moments in the tunnel.