Abstract
This study aimed to determine the reliability of the damage criteria that was adopted by the peak particle velocity (PPV) method and the single degree of freedom (SDOF) approach to assess the damage level of a box-shaped underground tunnel. An advanced arbitrary Lagrangian Eulerian (ALE) technique available in LS-DYNA software was used to simulate a symmetrical underground tunnel that was subjected to a surface detonation. The validation results of peak pressure into the soil revealed a good consistency with the TM5-855-1 manual within differences that were much less than previous numerical studies. The pressure contours revealed that the blast waves travelled into the soil in a hemispherical shape and the peak reflected the pressure of the tunnel that occurred immediately before the incident pressure reached its highest value. The assessment results proved that the criteria of the above methods could efficiently predict the damage level of a box-shaped tunnel under different circumstances of explosive charge weight and lining thickness at a depth of 4 m within slight differences that were observed during van and small delivery truck (SDT) explosions. However, the efficiency of both the methods was varied with the increase of burial depth. Whereas, using the PPV method significantly underestimated or overestimated the damage level of the tunnel, especially during SDT and container explosions with a lining thickness of 250 mm at burial depths of 6 and 8 m, respectively, the damage level that was obtained by the SDOF method greatly matched with the observed failure modes of the tunnel. Furthermore, new boundary conditions and equations were proposed for the damage criteria of the PVV method.
Highlights
In the last decades, the increase of terrorist attacks on underground tunnels, such as the bombings of Moscow, London, and Belarus, has highlighted the horrible effects of these events
The damage assessment was performed via the single degree of freedom approach (SDOF) that was proposed by Fallah and Louca [27], which mainly depends on the lateral displacement of structural members, and the results proved that the tunnel with 500 mm lining thickness was collapsed at a burial depth of 4 m during the surface explosion of a container truck
The pressure contours proved that the blast waves travelled inside the soil in a hemispherical shape before and after inserting the tunnel structure, which considerably reduced the values of incident pressure by obstructing the propagation of blast waves to large depths
Summary
The increase of terrorist attacks on underground tunnels, such as the bombings of Moscow, London, and Belarus, has highlighted the horrible effects of these events. According to the previous records, explosion attacks via a vehicle was the most used method by terrorists to achieve these assaults due to their massive charge power, high success rate, and severe destruction [1,2]. Tunnel structures could be subjected to internal or external blasts. The new control and security systems have been successfully used to monitor the internal blast inside a tunnel [3,4]. External explosions, are the most likely to achieve their purpose due to the absence of proper technology to detect these events before occurring [3,5,6]. There are no records available for a field trial due to the difficulties to acquire such a study in terms of cost and safety
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