عنوان مقاله [English]
Metropolitan underground tunnels is increasingly used these days. Besides, Iran has strategic importance in the Middle East meanwhile risking always military attacks of hegemonic countries and local terroristic activities. Concerning the mentioned points, it is crucial to investigate and analyze such structures under explosive loadings. This research focuses on the most critical scenario of damage distribution in the tunnel covering cause by TNT explosion. Moreover, the effects of soil overburden height as well as the amount of explosive material is studied on the maximum stresses and deformations created in the covering of twin tunnels under 4 explosive loadings of 15, 30, 45 and 60 Kg TNT. At the end, the effect of soft soil rehabilitation is assessed on the improvement of tunnels covering response under explosive loading.
Chio et.al (2006) studied the response of underground structures subjected to the explosion through nonlinear analysis . In 2006, Gui et. al investigated the effects of ground surface explosion on the tunnel of Taipei Shongsan airport. Two dimensional solution of the problem by Gui et. al has been in the line of its simplification . Lui has focused on the effects of explosion in New York subway. The conducted numerical investigations have been mainly two dimensional. The researchers mostly believe that plane strain assumption in the modeling is dramatically conservative in the explosion issue.
Methodology and Approaches
In this research, soil and tunnel have been subjected to the inside ground explosive loading in tri- dimensional form using ABAQUS6-11-1 finite element software. The explosive loading has been estimated through empirical relations of compression applied to the underground structure due to the explosion. Besides, the soil has been simulated by Druker Prager and the tunnel covering by Concrete Damage plasticity behavior models. Here, the effects of different parameters are investigated on the responses of twin tunnels under explosive loadings.
Results and Conclusions
The brief results of this investigation are as follows:
1- Increasing in the overburden height will cause the reduction of stresses and deformations in the covering of tunnels;
2- The most critical scenario of damage distribution in the tunnel section is in the overburden height of 10m under 60Kg TNT of explosive loading; the highest width of created crack is 91mm. the highest the height of soil overburden is, the more the created damage is in the tunnels covering under internal explosion;
3- The strength and stiffness of the ground should be rehabilitated in the soft soil surrounding the tunnel. The maximum stress is reduced for 44% with increasing the thickness of tunnel surrounding soil for 1m;
4- The maximum stress created in the tunnels covering is reduced by increasing the stiffness of soil. This reduction in the stress response is stopped in the status of increasing the thickness from 3m to 4m.
5- The stresses created in the tunnels covering are reduced with increasing the soil stiffness. The maximum stress remains approximately in a constant range in different values of soil strength.