Vízügyi Közlemények, 1962 (44. évfolyam)

4. füzet - IX. Könyvismertetés

(29)* A sink well and discharging canal are integral parts of all methods, by which the depth, respectively the extension of the settling pond can be controlled and the removal of clear supernatant water can be ensured (Figs, 15 and 16). Chapter IV is devoted to the mechanics of settling, in connection with which the physical properties of the slurry as building material are first described. The physical properties of the mixture consisting of solids and water are governed mainly by the particle-size distribution of the solid phase and the concentration of the slurry, while the other factors (specific gravity, density, viscosity, temperature) can in most cases be neglected. Parameters suitable for describing concentration are the percentage by weight (S), the percentage by volume (T), the solid : fluid ratio (Sz/F

) and the solids content (G tons/cu.m). The relationship between these and the specific gravity of the slurry is expressed in a mathematical form by Eqs. (1), (2), (3) and (4), and graphically in Fig. 17. The development of silted slopes is considered hereafter, in which two sections can be distinguished, namely that above the watersurface, controlled by laws of sediment movement and silting, and that under the watersurface, to which the laws of settling apply. The structural part on which the embankment relies for its stability is deposited over the section above the watersurface. Detailed attention is devoted to the movement and deposition of the solid phase. Some authorities attributed two types of textures to hydraulically placed earth structures: macro-stratification, ensuing where the solids are placed above each other with an alternating particle-size distribution, and consequently where it is inhomogeneous along the embankment axis. Stratification of this kind is "detrimental to stability, but can be avoided by correct organization. Micro-stratification is the consequence of periodically ravelling waves, respectively of the turbulence of the slurry. Its order of magnitude is smaller than 1 mm. This stratification is impossible to avoid. The steepness of the silted slope is governed by the particle-size distribution of the solids, by specific gravity, the shape of the particles, by the concentration of the slurry, etc. The slopes are very flat, inclined from 1:20 to 1:50 (Table II), and for fine sandy silt the authors observed it to be flatter in the case of longitudinal flow than in that of radial flow (Fig. 19). Based on the experimental results of the Soviet Institute VNIIG (Fig. 20) an empirical formula, Eq. (5), has been developed for the average slope inclination, and the equation of the curve which is convex from above, Eq. (6), was also determined there (Fig. 21). Other Soviet researchers advocate the validity of Eq. (7), the constants for which have been compiled in Table III. Over the underwater section the slurry of reduced solids content enters into the settling pond and proceeds as an underwater density current (Fig. 22). The particles are maintained in suspension by the vertical velocity components, and full settling takes place at the distance Lh from the watersurface, Eq. (9) and Fig. 23. Experiments carried out at the Soviet institute VNIIG concerning the underwater silted slope (Fig. 4) have shown the inclination of the slope to depend on the particle-size distribution and on specific intensity. Informative values of Lh can be obtained for coarse and fine particles from Eqs. (10) and (11), respectively. In keeping with the classification of the solids, the physical properties of the material undergo changes and show differences below and above the watersurface. No theoretical solution" has as yet been developed. According to approved practice a silting test is necessary at major structures. Results of a silting test conducted in Hungary are shown in Figs. 25 and 26, while the main characteristics of the Mingetshaurydam, built in the Soviet Union by the trestle-less method of construction have been compiled in Table IV. The density and consolidation of silted embankments is discussed in subsection 4. The density of the part above the watersurface is governed by the density of the slurry, by the particle-size distribution and by uniformity, as well as by the shape of the particles and by the conditions of silting. Embankments of higher density result from a slurry of lower concentration and low specific intensity. Results obtained at the Soviet institute VNIIG are presented in Fig. 27. The density of silted