EFFICIENCY OF CUTOFFS UNDER APRONS OF HYDRAlJLIC STRUCTURES

Abstract

An analytical solution has been obtained for the problem of seepage flow underneath hydraulic structures provided with two unequal cutoffs at the edges of -L their aprons. The structures are founded on anisotropic layer of varying thickness or

stratified soil of two or three layers. The derived equations have been used for computing the seepa'ge charactarestics. To facilitate the use of these equations, design charts have been obtained to calculate the relative uplift pressure distribution through the subsurface contour of the structures. Also, design charts have been derived for calculating the exit gradient at the downstream edge of the structure. The quantity of seepage discharge which seeps under the aprons can be calculated from the relevant charts. Solved examples are presented to clarify the use of the design charts in design process.

A computer prog am was designed especially to compute the data required for a wide range of structure dimensions. The program is friendly used and includes artificial intelligence unit to check the input data.

The analytical results was calibrated using field data under Naga Hammadi Barrage. The results gave good correlation with the piezometric readings under the apron of the barrage.

i..

Also, an electrolytic tank model was designed and constructed especially for verification of the analytical re;ults and for finding out the effective depth of the seepage zqne. A good agreement between analytical and experirr.tental results was obtained. From the obtained results and their discussion, the following conclusions can•be listed for the considered conditions.

I