The construction of a tunnel underneath the existing structure affects the stability of the foundation due to the ground deformation. The prediction of the interaction between a tunnel, soil, and existing structures always remains a challenge due to the wide variation in tunnel, soil, and infrastructure parameters. In the present study, a three-dimensional finite element analysis has been used to investigate the effect of tunneling in loose sand on the existing building with different foundation types (raft and isolated footing). A 6-story reinforced concrete (RC) building supported on an isolated and raft foundation with a different cover (C)-to-diameter (D) ratios (C/D) of the tunnel has been used in this study to investigate the Tunnel-Soil-Foundation-Structure Interaction (TSFSI). The behavior of soil medium and building are simulated using hardening soil with small strain and linear elastic model respectively. The tunneling-induced surface settlement and differential settlement of buildings supported on different foundations are systematically investigated and reported. The settlement in the building with isolated footing for different C/D ratios of tunnel increases to 3–5 times when compared with no tunnel case. Similarly, for buildings with raft foundations, the settlement increases in the range of 4–6 times when compared with no tunnel case. The study indicates that the isolated and raft foundation significantly influences the ground response to tunneling when compared with greenfield conditions.