Surface and underground structures are designed to withstand a certain load in a specific case, accounting for natural disasters such as earthquakes for certain scales. Underground structures tend to receive lower seismic impacts than surface structures. However, natural disasters shouldn’t be underestimated because they have the potential to damage a well-designed underground structure on a certain scale and even lead to failure. 

Seismic events are considered dynamic loads as they change over time and they require more computation costs and time due to complex calculations. The quasi-static method can be used to cut off unnecessary computation costs while still obtaining reliable results. Quasi-static is a method that simplifies theoretical and numerical methods in dynamic analysis (Ambrosio 2001). It is commonly used in the engineering field to design structures. The method’s main concept is applying a time-independent deformation profile on a static model assuming no working inertia force. 

In this study, tunnel internal forces were analyzed using a finite discrete method program, FLAC3D, by applying the quasi-static method to simplify the occurring dynamic load of a seismic event.