Nowadays, one of the most common methods for water transmission is through underground tunnels. Tunnels are in line with the fundamental principle of the passive defense for protection of water resources and are able to prevent any potential risks to water transmission lines. In this research, a numerical study has been employed to investigate the effects of surface explosion on the water transmission tunnels. Herein, by changing the distance of explosive materials as well as the thickness of concrete segments, response displacements and explosion effects on the concrete segments have been calculated. For this purpose, three concrete segments with the thicknesses of 0.2, 0.3 and 0.4 m were selected and subjected to the explosive materials located 0.5, 1 and 2 m away from them. The obtained results showed that the concrete segments with the thicknesses of 0.2 and 0.3 m experienced significant damage when subjected to 20 lb. explosive material at the distance of 0.5 m. It was found that burying the structures or embankments of the structures were among the best methods for damping the blast waves.