Vízügyi Közlemények, 1959 (41. évfolyam)
4. füzet - V. Kisebb közlemények-Ismertetések
(11) Experiments with double layers of fine and coarsely graded washed sands. Washed sands denoted c and b were used for these experiments. One of these (No. 9) was carried out with the coarse sand b forming the lower layer ; whereas the fine sand c was used for this purpose in the second (No. 10). Results and changes observed,are shown in Figs. 11 and 12, respectively. The fine sand formed the lower layer in the latter case. Investigation into the effect of silt content. Material denoted k was added in increasing proportions to sand e in this series of experiments. Gradation curves of materials investigated and results oblained are shown in Figs. 13 and 14, respectively. Sands containing about 7 per cent silt were generally found to be safe, as far as the development of boils was concerned. These mixtures were lifted as a coherent mass by water pressure, whenever the latter attained a value exceeding that of the tested material. Pressure relieving by means of filter wells. Arrangement and details of the filter wells used are shown in Figs. 15 and 10, respectively, while the results can be seen in Fig. 17. Drawdown established itself during these experiments as a satisfactory means to maintain the groundwater, which percolated under pressure, below the soil surface even under flow conditions which otherwise would have resulted in the development of elementary boils, or even soil failure. Filter wells proved to a certain degree effective in relieving the pressure also in case of a clay cover (Figs. IS and 19 ). So-called deep boils could be observed piping up from the sand soil beneath the cover, whenever the latter was pierced (Figs. 20 a —b). Practical conclusions. Information collected during these experiments is to be considered a welcome aid in practical flood protection work. Boils may develop during floods in cohesionless, granulated soils at the protected side of the levee if Lhe inore-or-less watertight cover layer is interrupted. Watertight, or semi-permeable toplayers over a granulated, cohesionless soil, capable of balancing by their weight the upward pressure acting from below, exclude the danger of soil failure (Fig. 21 a — 1). The development of boils may, however, start immediately, whenever the cover suffers some kind of damage (Fig. 21 — 2). Over small areas, boils may be suppressed by means of a standpipe. These, it should be noted, cannot be applied unless the cover is sufficiently deep to counterbalance the upward pressure. If the cover is thin, so that its weight is smaller than the hydrostatic pressure, the latter may be counterbalanced by building up a water head extending over a larger area by the aid of a dyke (Fig. 21 b — 1), or preferably by weighting the endangered zone down (Fig. 21 b -2), or by relieving the groundwater pressure by means of filter wells (Fig. 21 b — 3). (Author's summary translated by '/.. Szilvássy C. E.) AUFQUALMUNG UND GRUNDBRUCH Von H. Lumpi Doktor der technischen Wissenschaften (Ungarischer Text Seite 25—49) DK. 624.131.542 Verfasser untersuchte die Entwicklung von Aufqualmungen (geiserartige Aufbrüche von Qualmwasser) und die Bildung von Aufqualmungen einwirkenden Umstände und Faktoren bei der ungarischen Forschungsanstalt für Wasserwirtschaft im Rahmen des unter der Leitung I). Ihrigs begonnenen ausgedehnten IIochwasserabwehr-Forschungsprogramms im Jahre 1957. Ziel der ausgeführten Versuche war das Erreichen solcher praktisch leicht auswertbarer Ergebnisse, welche der Hochwasserabwehrpraxis behilflich sind, das nähere Kennenlernen der verschiedenen Phasen der Aufqualmung und auf diesem Weg die Entwicklung einer richtigen Abwehrmethode der Ursachen der Deichbrüche der Jahre 1954 und 1956 in Ungarn : der als Folge von Aufqualmungen eintretenden Grundbrüche. Verfasser führte die Versuche im Laboratorium mit Hilfe einer zu diesem Zweck konstruierten Einrichtung aus. Im Apparat War es möglich, den Vorgang der nach
