With the rapidly developing network of underground structures, intersections of tunnels, pipes, shafts, and adits are inevitable. Depending on how many passages meet at a point, there could be T, Y, or + type of intersection. Previously, a study has been carried out investigating the behavioral effect of impact on tunnel intersection. The purpose of the present study is to introduce further development in the understanding of tunnel intersections. This is attempted by varying tunnel diameter of branch tunnel and studying its effect on T-intersection. The study is carried out numerically using ABAQUS/Explicit module which is based on FEM. Both the main tunnel (MT) and branch tunnel (BT) are circular in shape. The diameter of the main tunnel (D) is kept 5 m for all the cases whereas diameter of branch tunnel (d) is variable. Overburden depth of 5 m above the main tunnel is kept constant for all cases. The impact location is above the center of the main tunnel. Six cases are studied with diameter ratio d/D equal to 1.0, 0.9, 0.8, 0.7, 0.6, and 0.5. Crown deformation is one of the most important and evident responses for assessing the damage when the tunnel model is exposed to impact load. It is found to show a decrease in values with decreasing d/D. The damage is also quantified in terms of longitudinal and lateral extent from the impact location along the crown. An increase in longitudinal extent and a decrease in lateral damage extent is observed. However, case d/D = 0.5 shows a decrease in lateral extent value and a considerable increase in longitudinal extent, indicating that the impact load in this case is solely resisted by the main tunnel. The trend observed in the results is attributed to the cover depth transition from main tunnel to branch tunnel.