Investigation on the performance of blanket, cutoff wall and synthetic cover for the control of seepage and piping in earth dams

This study firstly presents a review on the different methods for seepage and piping control of earth dams. Then, the capability of an upstream blanket, cutoff wall, and synthetic cover was compared for reducing of seepage discharge and exit gradient using SEEP/W software as a numerical simulation model. For this, a typical section of an earthen dam was considered. Totally, 54 tests were conducted under the different conditions of the upstream head, situation and depth of cutoff wall and upstream synthetic cover. For each test, the values of seepage discharge and exit gradient at the toe of earth dam were calculated. The results show that the presence of an upstream blanket can not reduce the seepage discharge and exit gradient, significantly. For example, the design of upstream blanket with the length of 45 m, only reduces the seepage discharge and exit gradient about 0.3% and 7.3%, respectively. On the other hand, by using an upstream synthetic cover the seepage discharge and exit gradient can be more reduced about 67.5% and 65.5%, respectively. The results also show that the best situation of the cutoff wall for the control of seepage discharge and exit gradient is in the middle of the earth dam. This can reduce the seepage discharge and exit gradient about 40% and 23%, respectively. This study presents a comparison about reducing the seepage discharge and exit gradient by using a combination of a cutoff wall with an upstream blanket and synthetic cover as the two different cases. The seepage discharge (exit gradient) was reduced about 40.4% (10.6%) and 63.3% (44.6%) for the two above cases. It is concluded that the best way for reducing the seepage discharge is the use of upstream synthetic cover with a cutoff wall in the middle. It is believed that the optimal design of a drain hole reduces the seepage discharge and exit gradient, simultaneously which requires furthering studies.

Keywords:

Seepage , Exit Gradient , Earth Dams , Cutoff Wall , Blanket , Synthetic Cover