Effect of Horizontal Drain Length and Cutoff Wall on Seepage and Uplift Pressure in Heterogeneous Earth Dam with Numerical Simulation

Design of earth dams and their problems are important during construction and after it, because of their potential hazards and failure for downstream population. This study focus on the effectiveness of using horizontal drain and cutoff wall in reducing seepage flow from an assumed heterogeneous earth dam. For this purpose various horizontal drain lengths and cutoff wall depth examine under the earth dam in different location of foundation. Seepage analysis, hydraulic gradient and uplift pressure, are computing by numerical simulation, using Seep/w software. Results show that increasing horizontal drain length, cause slightly in increasing seepage rate and increasing hydraulic gradient. Optimum location of cut off wall for reduction of seepage rate and piping is in the middle of dam foundation. By increasing in cut off wall depth, seepage from earth dam and its foundation is reducing. Different location of cut off wall in dam foundation has little effect on exit hydraulic gradient and always it is less than unity. Installation of cut off wall in middle of foundation, results 19.68 percent decreasing in hydraulic gradient respect to existent of cut off wall in upstream of dam.