Evaluation of the Environmental Impacts of Groundwater Levels Drop Due to the Excava-tion of Large-Scale Tunnels (Case Study: Kouhin Rail-Way Tunnel)

Today, one of the challenges in safety management of under-ground excavations is the water inflow into them. The tunnels and underground constructions are causing to remove a pile of soil and rock area and significant changes in the state of tension it’s around environment. Invasion of groundwater in-to the excavation area is a major problem in excavation of tunnels that is located below the hydrostatic levels. The un-derground-water inflow into the tunnels is an important issue in the tunnel engineering. The subsidence of the ground in hydrostatic levels, reduce the aqueduct water resources and springs that are located in downstream of the tunnel, are en-vironmental problems of the tunnel excavation operations. In the present study, the groundwater inflow into the Kouhin tunnel railway is modeling with FLAC2D software. The effects of groundwater inflows in the tunnel that while excavation are studied by numerical model. In other hands, initially in-vestigated the adverse environmental effects caused by the Kouhin railway tunnel excavation (subsidence the ground water levels and changes in the groundwater inflow in the region) and then provide some strategies for reducing these effects. The strategies that can be used in prevention of groundwater flow into the underground tunnels are: Under-ground water level recovery with application of concrete sealing operations without drainage and simultaneous use of forepoling methods that to be presented as a solution to re-duce environmental impact. Doing this requires using of con-crete lining with high strength properties to withstand hydro-static pressure of water collected on the back cover.