Conclusion
This paper studied the seismic behaviour of damaged tunnels. It was observed that the damage tunnel is subject to much higher dynamic stress than the undamaged tunnel. Also, lower frequency aftershocks can be more devastating in some conditions. Predominant horizontal dynamic stress frequencies increase with increased input motion frequencies for rigid tunnels. In flexible tunnels, horizontal dynamic stress frequencies do not change much with changes in input frequency. Dynamic stress amplitude is much larger for the flexible tunnel compared to the rigid tunnel. Dynamic stresses in soil away from the tunnel are greater for damaged tunnels compared with undamaged tunnels. Also, it does not depend on the degree of damage. However, a more detailed study of damaged tunnel behaviours during an earthquake should be conducted. The inside deformation of the tunnel is an important parameter that must be considered to ensure serviceability of underground spaces. Finally, the appropriate non-linear numerical model can be developed to simulate damaged tunnels seismic behaviour.
