Adverse Impact of Earthquake Seismic Loading on Angular Offset Tunnels and Effects of Isolation Grout

This paper investigates the effects of seismic loads on tunnels in an attempt to provide better protection from earthquake shaking. Dynamic analysis of angular offset tunnels was performed, and the tunnels’ behavior under earthquake shaking and their response when using seismic isolation were analyzed in detail. The time history analysis was used to compute the stresses and deformation that develop in the tunnels during seismic events. Earthquake records with different frequency spectra were applied as seismic excitation to the twin tunnels. The excitation was applied normally to the tunnel axis, with peak ground accelerations of 0.10 g–0.30 g. The seismic event lasted 15 s, with a time step of 0.02 s utilized in the numerical analysis. Finite element modeling was employed to simulate the soil–tunnel interaction. Numerical models simulated twin tunnels passing through soft clay or stiff clay, with various earthquake records applied as seismic inputs. The effects of a silicon-based isolation material composed of silicon oil and fly-ash were compared with the use of traditional grout. The numerical model results show how seismic isolation affects the stresses and deformations that happen in tunnel bodies during earthquakes.

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