Performance of Cutoff Walls Under Hydraulic Structures Against Uplift Pressure and Piping Phenomenon

This study is focused on a numerical method to investigate the performance of cutoff walls system against uplift pressure and piping phenomenon. The parametric study has been conducted on the variation of cutoff wall parameters such as inclination angle of one cutoff wall in upstream and downstream side of the hydraulic structure, their length in upstream side, their spacing and number of cutoff walls under hydraulic structure. The results showed that using inclined upstream cutoff wall θ = 70° and θ = 90° was beneficial in increasing the safety the hydraulic structure against piping phenomenon and uplift pressure, respectively. Using downstream cutoff wall with any inclination angle decreased the safety against uplift pressure, and the best inclination angle of the cutoff wall at the toe of the hydraulic structure in increasing the safety against piping phenomenon was θ = 130°. Increasing the length of the upstream cutoff wall increased the safety against uplift pressure and piping phenomenon. The use of the larger spacing between two vertical cutoff walls decreased the safety against uplift pressure and increased the safety against piping phenomenon. Finally, the best number of cutoff walls in increasing the safety against uplift pressure was three and also increasing the number of cutoff walls increased the safety against piping phenomenon.