Analyzing the Effects of Explosions in Twin Tunnels on Lining of Accident Tunnel and Adjacent Tunnel with Different Shapes

Recently, public places and underground transport facilities such as subways and urban transport tunnels and routes have been targets of terrorists. Twin tunnels are built because of their structural strength and ease of construction. In this study, the behavior of tunnels with different cross-sectional geometries was examined numerically by FLAC under the impact of explosive forces. The results suggested that the performance of tunnels with a horseshoe section performance will be better than rectangular. In recent decades, there have been reports about explosion in tunnels. In this article, the performance of twin tunnels with three different shapes under internal explosion was studied. Consequently, horse-shoe tunnels have better performance. Stevens et.al. have studied the impact of surface explosions on tunnels in different conditions. Ghaemi explained the effect of emission of missile compressive waves and their impact in continuous and discontinuous environment. Liu presented the nonlinear response of tunnels buried under explosive loading. Lee studied the stability of a tunnel which was adjacent an exploded tunnel. Tian studied the dynamic response of multi-story buildings affected by explosion in one of two twin tunnels. In the previous studies, the effect of cross-sectional shape of twin tunnels has not been investigated. The shapes of twin tunnels were adopted according to code 161 of ministry of road and urban development. Four types of twin tunnels were considered. The primary section is the combination of 2 circles with 12.5 and 5.8 meter radii for each tunnel. The first suggested section is a rectangle with 10m width and 6m height for each tunnel. The second section is a circle with 12.5 radius and a line with 10 meter length for each tunnel. The third section is the combination of 3 circles with 12.5, 6.4 and 2.9 meter radii for each tunnel. FLAC was applied. Mohr-Coulomb failure criteria was used for soil.
Results and Bending moments and axial force in the crown of the damaged tunnel and adjacent tunnel were obtained for four different cross-sectional shapes. The results showed that the stress caused by the detonation was much lower than the compressive strength of concrete, while bending moments are high. Therefore, when an explosion occurs, rectangular tunnels have poorer performance compared to other types of the horseshoe tunnel. Among the tunnels with horseshoe section, the second section shows a good performance against explosion.