Tunnels are often constructed to facilitate transportation networks such as roads, railways, and subways. Regardless of the specific use, tunnels at larger depths encounter challenges like soil stability, groundwater ingress, and geological hazards. This paper primarily deals with the numerical investigation of vulnerability assessment of circular twin tunnels on both frictional and cohesive soil. Twin tunnels were constructed in a successive manner, i.e., one tunnel was completely constructed using Tunnel Boring Machine (TBM), followed by the construction of the second tunnel. The interaction effects of closely spaced twin tunnels in terms of transverse ground settlement and variation in internal forces associated with tunneling using TBM were analyzed at constant tunnel diameter. For the twin tunnel analysis, the spacing was kept 1.5 times the diameter of the tunnel. Variation of axial force and bending moment was analyzed along the length of the tunnel at two different sections. Settlement at both surface and crown was found to be higher in clay as compared to sand. At the invert, the variation was complex due to the boundary effect. The axial force was found to be increasing in clay compared to sand, and the variation of the bending moment is more complex. Existing tunnel shows a slight (around 20%) increase in axial force after the construction of the second tunnel, and the newly constructed tunnel shows a negligible variation in axial force (around 2%) as compared to the existing tunnel in both sand and clay. At the same time, the existing tunnel shows axial force variation around 200% for a 6m diameter twin tunnel when comparing with that of single tunnels of the same diameter. The twin tunnel shows higher settlement than the single tunnel in both sand and clay. To summarize, twin tunnels in clay experienced higher settlement at surface, crown, and invert level as well as larger axial force and bending moment as compared to those of twin tunnels in sand.