Underground facilities serve several purposes as an essential part of the infrastructure of modern society. Subways, railroads, highways, material storage, sewage, and water transportation are applications of tunnels. Recently, increase in the frequency and magnitude of earthquakes have led to focus on the actual behavior of underground tunnels not only under static loads but also under dynamic effect of earthquakes. This study investigated 2D-numerical model circular tunnels under the influence of different earthquake records for sandy soils with different consisties. The soil types were dense, medium dense and loose sandy soils were studied. Three earthquake records, varying in peak ground acceleration (PGA) values and duration [Olympia earthquake (PGA= 0.16g and T= 89.08sec), Kalamata earthquake (PGA= 0.331g and T= 25.88sec) and Northridge earthquake (PGA=0.883g and T= 59.98sec)] have been conducted.
A parametric study for circular tunnels in different soil states under static load and earthquake dynamic loads was examined. Specific points were observed to monitor deformations and stresses. Comparing the behaviour of tunnels under static load and earthquake has been illustrated. The analysis of results shows that the duration of earthquake records has a greater impact on horizontal displacement than PGA values. Peak ground acceleration (PGA) significantly affects vertical displacements, bending moments and axial forces. Axial forces are almost constant under earthquake records with PGA less than 0.331g, whereas PGA more than 0.331g increases slightly. Finally, the effect of earthquake records should be considered in tunnels behaviour and design to avoid permanent deformation, stresses or collapse of the tunnels.