This article describes briefly the main assessments on the approaches used by engineers in quantifying the seismic effect on an underground structure, both referring to deterministic either probabilistic methods. However, the main purpose is that of proposing a new simplified approach to evaluate through numerical simulations the ovaling effect on tunnels’ cross sections. This method was initially verified with the closed form solutions for circular shapes and subsequently applied to acquire the stresses acting on the lining of tunnels characterized by complex geometries.

This study proposes a method that is as consistent as possible with the common procedures nowadays adopted to evaluate the effect of seismic motion in tunnels. As a matter of fact, the geometry of most of the cross sections in the Istanbul Metro underground structure is not simple enough to make proper use of the closed form solutions; thus, a numerical method has to be viewed as the only possible option to assist the design process. Nevertheless, a simple method of analysis was chosen for evaluating the ovaling effect, which takes into account the time dependent acceleration spectrum, instead of a complete coupled analysis, which would have required too many different structures and geological conditions to optimize the time cost of the procedure.