عنوان مقاله [English]
Consequently, horse-shoe tunnels have better performance.
Recently, public places and underground transport facilities such as subways and urban transport tunnels and routes have been the targets of terrorists. In this regard, there have been reports about explosion in these tunnels. 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 using the FLAC software under the impact of explosive forces. Thus, the performance of twin tunnels with three different shapes under internal explosion was studied in this research work. The results suggest that the twin tunnels with horseshoe cross section compared to rectangular cross section have better performance.
Sadegh azar et.al. (2009) studied the impact of surface explosions on tunnels in different conditions. Ghaemi (2011) explained the effect of emission of missile compressive waves and their impact in continuous and discontinuous environment. Liu (2012) presented the nonlinear response of tunnels buried under explosive loading. Lee (2006) studied the stability of a tunnel, which was adjacent to an exploded tunnel. Tian (2008) studied the dynamic response of multi-story buildings affected by explosion in one of the twin tunnels. The effect of cross-sectional shape of twin tunnels that have not been investigated in these studies, is examined in this paper.
Methodology and Approaches
The shapes of twin tunnels were adopted from the code 161 of Ministry of Road and Urban Development. In this study, four types of twin tunnels have been considered. The primary section of the twin tunnels is the combination of 2 circles with the radii of 12.5 and 5.8 m in each tunnel. The first suggested section for the twin tunnels has a rectanglar shape with 10 m width and 6 m height in each tunnel. The second section for the twin tunnels is in the form of a circle with the radius of 12.5 m and a line with the length of 10 m in each tunnel. The third section of the studied twin tunnels is a combination of 3 circles with the radii of 12.5, 6.4 and 2.9 m in each tunnel. The FLAC software was used for this study. In this study, Mohr-Coulomb failure criteria for soil was considered.
Results and Conclusions
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 horseshoe tunnels. Among the tunnels with horseshoe section, the second section shows a good performance against explosion.