Evaluation of geological hazards along the Karaj water conveyance tunnel using multiple approaches and GIS

The prediction of geological hazards prior to tunnel excavation is of paramount importance, as understanding these hazards is fundamental in tunnel design, route selection, drilling technology choice, maintenance, and the construction of associated structures. The most significant geological challenges that may occur during and after tunnel excavation include groundwater inflow, tunnel face squeezing, convergence of tunnel walls, the collapse of fractured zones, and rockburst. These hazards can lead to unforeseen costs, operational disruptions, and schedule delays. Therefore, comprehensive assessments of geological hazards are essential before commencing underground projects to facilitate informed design decisions. In this study, we apply various analytical, numerical, empirical, and semi-empirical methods to estimate and assess geological hazards associated with the Karaj water conveyance tunnel, Iran. These hazards include water inflow into the tunnel and the tunnel's susceptibility to squeezing and rockburst. The identified risks along the Karaj water conveyance tunnel route are then classified within a GIS environment. Maximum water inflow into the tunnel corresponds to sections having high rock squeezing, primarily in fractured and faulted zones. These zones, along with sections of the tunnel characterized by low rock mass quality but high rock mass yield, exhibit the highest risks for potential squeezing and rockburst.