الفهرس 
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Abstract
Seepage is one of the most important factors that affect the stability of a heading-up structure. Using sheet piles under the aprons of heading-up structures increases the percolation length and decreases the hydraulic gradient and hence provides more safety against piping and uplift under the structure’s apron.
In this study a SEEP2D finite element model is implemented to study seepage under the apron of a heading-up structure formed on pervious soil and provided with upstream and downstream sheet piles at its ends. Different scenarios for the thickness of pervious layer under the apron, the length of the apron and the depths of upstream and downstream sheet piles were studied.
Results show that the assumption of the outer and inner faces of both upstream and downstream sheet piles having the same weight while designing aprons of hydraulic structures is a weak one. The head loss actually varies along each face of the upstream and downstream sheet piles. Design charts for both upstream and downstream sheet piles are also presented. These charts can be used as a tool in practical design for aprons of heading up structures formed on pervious soil and provided with upstream and downstream sheet piles at the ends of the apron.