Application of the Seep 3D Software in Modeling the Effects of Cutoff Walls on the Reduction of the Seepage Pressure and Exit Hydraulic Gradient Under Hydraulic Structure

Seepage under hydraulic structures built on permeable foundations may cause internal erosion، boiling and piping، and in the extreme cases، overturning of the structure due to the development of the uplift pressure. Therefore، predicting the location of the seepage line، the uplift pressure، and exit hydraulic gradient are vital in the safety of such structures. Installation of the cutoff walls underneath such structures is an approved method of seepage loss and hydraulic gradient reduction. The Seep/3D software، which employs finite differences، was used in this study to developed more than 1000 models to pinpoint the location of cutoff walls and their depth of installation that minimizes the uplift pressure and exit hydraulic gradient. It was revealed that a cutoff wall installed at the lower toe of the structure theoretically presents piping، and one located of the upper toe reduces the uplift pressure. These results are depilated in a series of curves، which allow a designer to anticipate solutions to the seepage problem without a computer code and، to obtain the flow characteristics and achieve an optimum design by spending less time for making a quick and correct decision.