Vízügyi Közlemények, 1973 (55. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(98). Etcheverry (1) without modification, in that the mean depth is introduced for the depth term. If the value of the proportionality coefficient C, the magnitude of which depends on the soil type, is assumed in a manner to agree with the extreme values of the categories defined by Etcheverry, the approximation will be on the side of safety. This, however, does not entail necessarily—owing to the slight losses obtained as results—the enlargement of the canal cross-sections (this being unnecessary). MOVEMENT PHENOMENA IN HYDROTECHNICAL STRUCTURES BUILT ON ALLUVIAL SOILS by Dr. F. Hamvas, Civ. Engr. (For the Hungarian text see pp. 435) The movement of hydrotechnical structures founded on alluvial soils is analysed for the case, where a practically impervious clay layer is situated at 15 to 20 m depth below the foundation level. The movements predicted theoretically (Fig. 1 ) were compared with the results of observations (Fig. 2) made with the help of a set of bench marks distributed over the structure. The construction history of the Kisköre Barrage built on the Tisza River is described ( Figs. 3 and 4) and the movements observed on several component structures during construction and after impoundment was started, are analysed in detail ( Figs. 6-11 ). The results of these comparative studies can be summarized as follows: — In the case of hydrotechnical structures for which deep and large construction pits must be excavated, both heaving and settlements should be anticipated. — The movements of structures can be investigated in an absolute and in a relative system alike. The movements related to an absolute datum (e.g. Baltic, or Adriatic mean sea level), as well as those considered alone, or relative to adjacent component structures may reveal considerable differences. — The levelling work for checking the structures for movement must be started from bench marks situated at least 350 to 500 metres away from the construction area. The elevation of this bench mark should be checked at least once, or twice each year using a reliable distant point (mark) as basis of reference. — Flooding of the construction pit, or starting impoundment will increase the water load on the clay layer and act as an additional external load, so that the structure may continue to settle, regardless of the uplift force acting already. — The movements of structures are influenced by the excavation and backfilling operations in the vicinity of the construction area, yet also by the construction work on the structure itself. The magnitude of these movements may attain an order of magnitude affecting even structural conditions (see Fig. 11). — Fluctuations in operational loads result successively in movements characteristic for the period of secondary consolidation (Figs. 12 and 13). It is of interest to note that the movements of the structure are governed by the water load acting on the clay layer at greater depth below the foundation, in that the structure will settle and heave in accordance with an increase, or decrease of this water load. The uplift force is insignificant in this respect. No hysteresis curve has developed, the load-settlement curve is approximately a linear one. The times of observation must be selected with great care ( Fig. 14) otherwise the results will be misleading and give rise to incorrect conclusions concerning both construction and structural behaviour. BBIEF PUBLICATIONS AND REPORTS Dr. Nagy, László, Civ. Engr. : Stage forecasting in the United States (For the Hungarian text see pp. 458) The vast area of the U.S., the frequency of storms, as well as the distribution of precipitation and rains over time and area" have made the establishment of a well organized meteorological service necessary. Stages are forecast for various purposes