Effect of Width, Length and Position of Cutoff Wall on the Seepage Characteristics of Earth Dam

Abstract

Seepage is one of the main causes of failure of earthen dam. To encounter the seepage
through the foundation of dam, construction of cut off wall is a frequently used and a
conventional technique. In this study, several numbers of numerical analysis are performed
against different widths and lengths of the cut off wall for different positions along the cross
section of the dam to find out the appropriate one. All these analyses are performed for a
homogeneous dam with foundation soil being clay and silty clay. Numerical analyses are
conducted by SEEP/W (a sub program of geo studio). The numerical results depict that the
best possible position of the cut off wall is at the downstream toe of the dam. This is because,
in this position, most number of flow lines gets encountered by cutoff wall. It is also observed
that the effect of the width of cutoff wall on the total head and pore water pressure (PWP) is
negligible but it affects the velocity of seepage and total discharge. On the other hand, the
length of the cutoff wall controls all these flow properties. Clay foundation provided a better
result than silty clay foundation for all the cases to control the seepage through the
foundation of the earth dam.