The role of tectonic structures in conducting groundwater inflow to the second part of Zagros water tunnel - Kermanshah province

High local groundwater flow into rock tunnels is a technical and environmental problem for underground constructions. Geological structures such as faults, open fractures, and dissolution channels could play important roles in conducting ground waters to the tunnels. However, prediction of groundwater inflow from these structures using analytical and empirical method often failed due to given hydrogeological assumptions and simplification such as a homogeneous and isotropic porous medium around the tunnel. The Zagros water tunnel is located in the northwest of Kermanshah province. A huge amount of groundwater flow into the tunnel through fractures occurred during drilling of the second part of tunnel. The second part of tunnel passes through Pabdeh and Gurpi formations. A considerable amount of groundwater flushed into the tunnel when the Ilam Formation was penetrated, causing numerous problems and great damage to the drilling operation. The goal of this study is to identify the factors that influenced water flows into the tunnel. To this purpose, geological features of high flow rate zones have been identified and investigated. The highest input rate (800 l/s) was recorded in the zone Hz23 located in Kurdighaseman anticline. The relationship between geological features and the groundwater inflow into the tunnel indicated that faults play conveying role for ground water into the tunnel. Evaluation of high local groundwater inflow to rock tunnels based on characterization of geological structures is more reliable compared to available analytical and empirical estimation.