Experimental and Computational Characterization of Dynamic Loading and Structural Resistance of Tunnels in Blast Scenarios

Tunnels are key elements in modern traffic networks. Large-scale accidents and malicious threats, such as fires or explosions creating a blast loading, potentially carry very high economical and societal consequences. Compared to other statistically certain events, explosive-induced blasts in tunnels have an extremely low probability of occurrence but at the same time an enormous damage potential for structure, life, and environment. The paper presents a procedure for evaluation consequences of blast loading threat scenarios, focusing on the local and global structural integrity of tunnel constructions. Methods to capture the dynamic loading and the structural resistance, especially considering the dynamic soil response under large stresses and strains, are described. For that, a combined experimental and numerical approach is chosen, including characterization of the soil by dynamic triaxial experiments realizing stress levels of about 1 MPa, acting in 1 ms on the specimen. The analysis showed that the measured triaxial strength of the soil differed from the static by a factor of 2 for the friction angle. Furthermore, scaled experiments have been designed and conducted to demonstrate and investigate the behavior of a buried tunnel segment under blast loading. The results showed that realistic loading charges can cause massive cracking of the tunnel system and a soil sinking of up to 1 cm. Both experimental results obtained from the triaxial tests on the one hand and from the scaled tunnel experiments on the other hand have been validated using numerical models. The good agreement obtained is the essential input parameter for the evaluation of criticality in tunnels under blast loading scenarios.