Vízügyi Közlemények, Kivonatok, 1965

1. Az 1965. évi dunai árvíz - 1.1. Body K.-Csoma J.-Károlyi Z.-Szilágyi J.: Az 1965. évi dunai árvíz hidrológiai okai és lefolyása

(53) soil, the choice of the most suitable design should be governed by considerations of efficiency, costs, maintenance rate of seepage flow. Strengthening is possible by two alternative methods: a) by balancing uplift pressure acting on the underside of the top cover, or b) by reducing these pressures. Measures pertaining to the first group include: landward berms and sublevee basins, while those in the second group are: sealing the top cover on the riverside (impervious riverside blankets, or impervious backfilling of borrow pits), various cutoffs, drains and relief trenches (Fig. 6). Landward berms are always suitable for supporting the levee slope and for ballasting thin top covers overlying a permeable waterbearing sublayer. Such berms must always be constructed of pervious material. Where the corresponding material is not available in the required quantities, at least a filter blanket must be placed under the berm. Sublevee basins can be used under certain circumstances, as an emergency solution only where other methods of protection are less suited. Sublevees must be operated with great care. Riverside impervious blankets are suitable in combination with levees on permeable soil, or on top cover perforated (e.g. by borrow pits) on the riverside, for removing the point of seepage entry and the initial steepgradient section of the pressure line from the levee. Cutoffs and sheet piles extending into the foundation of the levee are unsuccessful, unless they penetrate at least 95% of the permeable sublayer in which the upward pressure on the top cover is developed. Filters can be used to depress the line of seepage within the levee, and thus for the protection of the landward slope, but also for reducing the detrimental effects of seepage in permeable soils underlying immediately the levee. In the case of very thin top covers relief trenches may offer the preferable solution. For the strengthening of levees along the Danube river an example is given in Fig. 7, where the subsoil of the levee is stable.