Cut-and-cover tunnels behavior at ultimate limit state depends strongly on the interactions between the foundation soil, the backfill and the reinforced concrete structure. Characterization of the potential failure modes of these types of structure necessitates taking into account every major mechanical property of each components. The influence of the structure plastic behavior on the ultimate limit state of the soil-structure system is discussed through a basic case study of soil mechanics. The ideal shape of embedded arches is also discussed.