Probable Hazards and Threats on Urban Tunnels during Operation

Nowadays in megacities, subways and urban tunnels are recognized as one of the most important key components of urban transportation network and its infrastructure. Construction of these infrastructures in developed countries and gaining efficient results as an outcome of their application in reducing urban transportation issues necessitates the requisiteness of attention on their widespread utilization in developing countries. However, the design and construction of such massive projects in the country which, remarkable costs are spent for, might always be involved with the occurrence of any hazard or threat. These issues are ever considered as one of the main challenges of tunneling during all three phases of design, construction, and operation, and in order to lead to the advancement and sustainable development of these underground structures in terms of construction and maintenance, the investigation of safety and risk assessment against these hazards and threats must be seriously taken into account. In this regard, the first step is the identification of hazards and threats and the investigation of the consequence of their occurrence on urban tunnels. In the operation phase, the study of various hazards and threats on urban tunnels shows that hazards including unintentional fire, collision of vehicles, entrance of surface water and flood into the tunnel, occurrence of earthquake, and negligence in maintenance and repair of tunnel, as well as threats such as explosion, emission of chemical, biological and radioactive agents, cyber-attacks, intentional fire, and subversive operations must be considered in the risk management and safety provision of urban tunnels.