Engineering Geological Hazards Along Doroud-KhorramAbad Railway Rock NATM Tunnels

Abstract The characterization of geological hazards holds significant importance in the context of underground spaces, specifically in tunnelling projects. This importance stems from its crucial role in determining the tunnel route, excavation techniques, and adopted risk management technologies. Tunnelling projects frequently encounter various engineering geological hazards, including issues related to ground conditions, groundwater levels, and in-situ stress regimes. Challenges such as encountering fault and crushed zones, mixed face formations, geological and structural instabilities such as wedge-failures and plan-failures, squeezing phenomena, karst formations, water inrush in the tunnel, hard and abrasive rock, landslides, and convergence are considered as primary causes of geotechnical risks in hard rock tunnelling. The primary objective of this study is to identify potential engineering geological hazards along the Doroud-KhorramAbad railway tunnels in Iran. The project spans 121 km, with 30 km comprising tunnels (13 tunnels) that have been excavated using the new Austrian tunnelling method (NATM). Detailed descriptions are provided regarding geotechnical considerations specific to tunneling. Based on the results of laboratory and field investigations, it has been determined that encountering crushed zone, structural instabilities and collapse as well as water inrush and rock fall, are the most significant hazards in this project. Introduction Railway tunnels used for underground transportation purposes have been widely constructed in recent years. Despite facing challenging geological conditions during construction, there remains a pressing need to effectively manage construction risks in complex and variable geological environments (Ren et al. 2016, Iegupov et al. 2018). Both highways and railways are recognized as efficient modes of transportation that play a crucial role in supporting the economic advancement of Iran. Consequently, the construction of tunnels has experienced a surge, positioning Iran as a country with the highest number of mountain tunnels.