Journal of Engineering Geology

Because most part of Iran country is located in a dry climate, construction of water conveyance tunnels is inevitable. One of the major challenges in the construction of these tunnels is inflow of water into the tunnel during the construction and operation phase. The Rozieh water conveyance tunnel whose length is 3200 meters is a part of water conveyance project to the Semnan city and it is located 30 k NE of Semnan city. In accordance with the drilled boreholes, the tunnel route has been classified into eight zones from the geotechnical view. Then the permeability coefficients of host rock were calculated using back analysis approach on the basis of numerical simulation results and water inflow quantity during the construction phase. A parametric study was done on the lining and cement injection zone permeability and the thickness of cement injection zone. According to this study, the effect of injection zone thickness variation on the water inflow quantity is negligible. So with the assumption of 3 meters thickness for the injection zone, the permeability coefficient of host rock after injection were evaluated. Dependent on the initial rock permeability, cement injection could reduce the rock permeability 10 to 1000 times. In addition, the water inflow into the tunnel was calculated using hydro-mechanical coupling analysis. According to this analysis, the water inflow calculated by the hydro-mechanical coupling analysis is 50 to 70 percent less than the hydraulic analysis.