Vízügyi Közlemények, 1959 (41. évfolyam)

4. füzet - V. Kisebb közlemények-Ismertetések

(56) The fundamental relationships expressed by Eqs. (22) and (25) and based on seepage resistances as well as on the characteristic lengths B

x and B

2 thereof, are suitable to take care of any change in the covering layers, or in seepage conditions, by the suitable modification of the characteristic lengths. In cases, where there is an adequately designed pressure relieving drain behind the structure, the head h

x must become zero at the axis of the drain. The constants C

1 and C

2 in the fundamental expressions can be determined by this condition, whereafter the characteristic length B

1 of the downstream side can also be reduced by the aid of Eqs. (61) and (62), see Example 2, Fig. 9. Neglecting the pressure relieving effect of the water volume emerging between the downstream toe of the structure and the drain, the effect of the latter can be computed approximately even if the drain discharges at a level below the terrain (Fig. 10, Eqs. (66) to (69)]. Approximating relationships between a gallery and the drawdown of an infinitely long row of wells have been established for identical yield by Forchheimer. Using these relationships and relying on data determined previously for the pressure relieving drain, preliminary dimensions of a pressure relieving well-row can also be predicted (Eqs. (70) to (84), Figs. 11 and 12, Example 3). In cases where the cover, either on the upstream, or downstream side of the structure, is composed, as e. g. in Fig. 13, of layers of different seepage resistance, the familiar equations can be used to compute the seepage discharge and pressure conditions at the boundary of the two layers. The characteristic length of the cover can hereafter be reduced on the downstream and the upstream side alike to the value pertaining to a homogeneous layer — Eqs. (85) to (95). If the layer denoted by II. in Fig. 13 has no resistance (7i

x

l = 0), expressions for the pressure relieving drain are obtained, however, if the same layer is completely impermeable (B„ = oo) the case of an infinite permeable layer arises, or, in scale model investigations, no sufficiently long equipment is available to permit the development of the flow pattern which becomes extended owing to the cover {Figs. 14 and 15, Eqs. (96) to (97), Examples 4 and 5

]. Several permeable layers below each other can be reduced to a single layer according to Eqs. (98) "and (99). Accuracy limits of the computation method are investigated in Chapter III. Compared with results of investigations conducted into permeable layers without cover by Pavlovsky and Dachler, it can be stated that the equations are applicable to layers without cover, if vertical water movement is assumed also in the upper 0,194 d

0 deep section of the impermeable layer. Consequently, in case of seepage without impermeable cover, 19,4 per cent of the total resistance is the vertical resistance. Therefore, this is the maximum error likely to be introduced by the simplifying assumptions. Tables 1 and 2 present a comparison with values determined by the method of Pavlovsky and Dachler. (Author's summary translated by Z. Szilvdssg, struct, eng.) PROCÉDÉ APPROXIMATIF POUR LE CALCUL DE LA FILTRATION DANS LE SOUS-SOL STRATIFIÉ D'OUVRAGES D'ART Par L. Galli (Voir texte hongrois et figures pp. 355—392) Les vallées des cours d'eau hongrois sont en général larges et plates. On ne peut donc y construire que des barrages bas, hauts de 8

—

15 m. La couche de base du fond de la vallée est généralement du sable graveleux recouvert d'une couche de transition susceptible de fluer, puis d'une couche argilo-vaseuse dite «couche de couverture» cohérente. Les dimensions et qualités moyennes des couches du sous-sol sont contenues dans la fig. 2. Dans ces vallées la hauteur de là retenue est réduite et de ce fait l'effet de la couche de couverture se fait fort sentir tant du côté amont que du côté aval. On doit donc prendre en considération cet effet en calculant la quantité de l'eau de filtration et dans l'examen des conditions de la rupture du sol.