Abstract
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 differ 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 different seismic inputs. Moreover, the soil non-linearity was taken into account adopting two different 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.
Highlights
It is becoming ever more evident that there is a growing need for tunnels, in order to solve the problems faced by transportation and utility networks
They are expressed in terms of: (1) the acceleration amplification ratio Ra, which is the ratio between the maximum acceleration at a given point and the maximum acceleration at the bedrock. This ratio was analyzed for the SS alignment and for the free-field conditions (FF) alignment (Figure 2); (2) the soil amplification function for the two SS and FF alignments: this is the ratio between the Fourier spectrum at the surface and the Fourier spectrum at the bedrock; (3) the surface response elastic spectrum in SS, compared with that provided by the Italian Technical Code [24]; and (4) the seismic bending moments in the tunnel, evaluated for four specific points on the contour of the tunnel(θ = 45◦, θ = 135◦, θ = 225◦, and θ = 315◦ )
As for the first comparison, relating to the different Vs of the analyzed soils, it was possible to Thethat, paper dealt withthe a case-history of thecaused underground network in including the an observe first of all, tunnel generally demagnification phenomena
Summary
It is becoming ever more evident that there is a growing need for tunnels, in order to solve the problems faced by transportation and utility networks. It is extremely important to assess the possible damage to the tunnel and to the aboveground structures as a result of earthquakes. Tunnels have experienced a lower rate of damage than aboveground structures [1]. Recent studies have documented significant damage suffered by tunnels due to seismic events [2,3,4,5,6]. The vibrations of aboveground structures may modify the dynamic response of tunnels [7,8]; at the same time, the presence of shallow tunnels may alter the response of aboveground structures. Most of the published papers consider only tunnel-soil systems [9,10,11,12,13,14,15], while a few consider tunnel-soil-aboveground structure systems (TSS systems) [16,17,18,19,20]
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