Theoretical Basis for Designing Seepage-Control Walls in Dam Foundations

The structures arranged using the method of «slurry trench cutoff wall» or using secant piles are frequently used as seepage-control elements in dam foundations. However, they are designed based on empirical approaches without theoretical validation. With the aid of theoretical modeling the author revealed main specific features of seepage-control walls stress-strain state. They work not only for cross bending but also are subject to bending in their own plane, as well as they perceive considerable vertical forces. These forces appear due to friction between the wall and soil. The author obtained empirical formulae which at preliminary design stages permit predicting maximum values of compressive stresses in the wall at the moment when vertical forces have maximum values. The study made it possible to verify the recommendations for selection of material for arrangement of seepage-control walls. As a rule, deformation modulus of the wall material should not exceed the deformation modulus of the weakest soil by more than two times. Clay-cement concrete or plastic concrete is recommended to be used for the wall material. Its compressive strength is provided due to lateral compression of the wall by lateral compression of soil and groundwater pressure. For not deep «hanging» walls it is possible to use concrete. The assessment was given of foundation deformation impact on the stress-strain state of seepage-control walls. Occurrence of weak interlayers in the foundation causes in the wall appearance of zones concentrating compressive stresses and additional bending deformations. In high dam foundations there is a danger of sharp decrease of the wall compression pressure due to deformations of the foundation lateral expansion. It is not recommended to use the cantilever pattern of the wall conjugation with the dam body, but arrange a concrete gallery above the wall head. Conjugation by a cantilever is possible only for the walls arranged at the edge of the dam profile.