Vízügyi Közlemények, 1962 (44. évfolyam)

4. füzet - IX. Könyvismertetés

(45)* INVESTIGATION OF UNDERSEEPAGE WITH TOP COVER ON THE WATER-SIDE By Dr. Gy. Kovács (For the Hungarian text see pp. 347) In the introduction earlier methods of calculating seepage characteristics are described, in which allowance has been made for the top cover on the water-side. These rely on the assumption of vertical seepage in the cover, and horizontal water movement in the waterbearing sublayer. The aim of the method to be described by the author is to extend the relationships derived earlier for the investigation of a homogeneous layer, to include the case of the waterbearing layer overlain by a top cover. The basic principle is to attach the part of the top cover under the levee to the levee foundation, while that beyond it is replaced by a layer having the same composition as the waterbearing layer, but of a depth increased in the ratio of the permeabilities. The resulting arrangement is that of a deep foundation slab, which can be transformed into one flush with the terrain. This system yields already to the method developed for the investigation of a homogeneous layer. For obtaining the desired result, the transformation equation mentioned above for the foundation slab has been determined by taking into consideration information published in the literature. Although the elliptical relationships derived are already a theoretical solution for the problem, but they are not suited for practical calculations. A less involved and more handy relationship could be derived by series expansion, or other approximation, but this form does not agree entirely with the actual process. In fact it can be demonstrated that even where the danger of hydraulic soil failure is not present, a drainage system must be created on the protected side for maintaining the natural state of soil water household, if the waterbearing layer is coarse-grained and horizontal seepage is appreciably in excess of evaporation. The actual condition ensuing as a result of these engineering measures can be approximated fairly well by the assumption of a seepage system covered by a top cover on the water-side only. Even this can be replaced by a layer having the same composition as that of the'waterbearing layer. The top cover on the protected side, extending to the first drainage chanel, or filter, is attached to the impermeable foundation. Beyond this point the bottom surface of the top cover is regarded as a horizontal potential line, to which the flowing water may emerge without restriction. In view of the fact that a pressure is exerted by the top cover on the flow system below it, and tends to balance thus to a certain extent the depression caused by the drainage system, this approximation is justified. The pressure characteristic for the potential line mentioned above can be described in terms of the level of drainage. The equation for transforming the resulting pattern (Fig. 4) has been derived, from which the relationships for calculating the significant values have been developed. The formulae given in earlier papers, by which the seepage volume, the distribution thereof in a direction perpendicular to the levee, and the width of the strip affected by seepage can be determined, have been compiled separately. In conclusion the application of the relationships suggested, are illustrated by a numerical example. At the same time it has been endeavoured to comprise all design aspects relating to the determination of steady seepage into a uniform method. (Translated by Z. Szilvássy)