Laboratory and field investigations, recently carried out while planning the rabble dams of the Nurek, Charvak, Kampyr-Ravat, and Verkhne-Tobol hydroelectric stations, by the Laboratory of Hydrotechnieal Constructions of the All-Union Scientific-Investigation Institute of Water Supply, Canalization, Hydrotechnical Structures, and Engineering Hydrogeology (VNII VODGEO), have revealed that the density of the placed material is governed by its grain-size composition and by the method of compaction. To make a quantitative estimate of the effect of these factors on the density of the talus, we can use the following dimensionless parameters which follow from the theory of similarity.'In estimalin~ the ~rain-size composition only: the coefficient of relative density r is equal to the ratio of the density 7mix of the mixture of coarse rubble of multifraction composition in the uncompacted (loose) state to the density of the separated fractions 70 in the same state, i.e., because the grain-size composition does not alter during compaction).In estimating the mode of compaction only: the degree of machine compaction n is equal to the ratio of the density of the mixture (or individual fractions) of coarse-grained material in the compacted state to the density of the mixture (or individual fractions) in the noncompacted (loose) state, i.el, 7 mix. com p. = h~comp _ const, ~q = 7mix. loose 70. loose
A generalization of experience in constructing rockfill and earth--rock dams during the two decades before and after the war performed by the prominent Soviet hydraulic engineer S. N. Molseev [i] showed that in this period two main methods of pioneer placement of the shoulders of such dams were used: in thick layers (up to 90 m) with compaction by a jet of water from hydraulic monitors and in thin layers (1-2 m) with mechanical compaction. In the opinion of E. E. Nonweller, general rapporteur at the Sixth International Congress on Large Dams, the first method provided the same density as with placement in thin layers with compaction and that it was the most efficient.
In planning and constructing earth dams, it is frequently necessary to use rock material excavated from low-strength and weathered strata, particularly in regions of the Urals, Siberia. the Extreme North and the Far East. In designing an earth-and-rockfill darn 41.5 m high with a 25-m hydraulic head and a central clay core having a volume of more than l0 s m s, the thrust prisms are constructed of weathered siltstones-sandstones obtained from the excavation of available pits (Fig. i). It is necessary to note that the weathering of weak interstratified siltstones and sandstones is accompanied by the formation of significant volumes of talus consisting of small thinly laminated plates and rubble over the course of a comparatively short period of rime. In this case, the clay content in this talus is low and, according to analyses conducted on average samples, less than 2.5 mm in size, is 12% in fine-rubble 35-year-old talus, and 11.2% in coarse-rubble 5-year-old talus. It should also be considered that siltstonez can be transformed into clayey argillites and, later, into highly plastic bentonite-type clays. In this connection, rock materials removed from these strata are not usually recommended for hydraulic construction (Standard Norm and Specification I-V.8-62). It was possible, however, to provide the basis for the use of similar materials in the dam under consideration. In this case, a portion of the upstream thrust prism within the limits of the variable water level is constructed of sound rock.Tests which we conducted indicated that rock materials containing up to 30% of weathered rock (siltstonesandstone types) possess adequately high structural properties and can be used for constructing low-head earthand-rockfill dams. The use of weathered rock from pits available near the hydraulic facility was found to be one of the basic factors that reduced the cost of the earth-and-rockfll dam by up to 20%. It should be considered. however, that when unconditioned local structural materials are used in dam construction, special studies should be considered in every case to investigate and evaluate their structural properties. This investigation should be conducted during all planning stages of the dam under laboratory and, by all means under natural conditions, bearing in mind the degree of weathering exhibited by the rock and the classification of the final weathering products [i].Together with other physicomechanical indicators, the permissible (within the limits set forth by the Standard Norms and Specifications 11-53-73 and I-V.8-62) content of clay particles in the final weathering products. which are formed under natural conditions during operation of a structure, may serve as the basic criterion for solving the problem of the applicability of rock material derived from weathered strata In hydraulic construction. Data obtained from engineering-geologic research, which enable us to ascertain the possible weathering period of a rock material down to the clayey fraction, or the results of field observations and labo...
The current SNiP [Construction Specifications and Regulations] II-A. 12-62 [i] envisage that the seismic resistance of a dam made of local materials should be calculated, for example, by the method of circular-cylindrical slip surfaces. The seismic loads are regarded as inertial forces acting at the centers of gravity of the mathematical elements into which the cross section of the dam is divided. However, the norms do not envisage calculation of the stability of the embankment slopes; planning organizations usually use Mononobe's formula or one of its variants. In these formulas, the stability of an embankment slope is assessed from the stability of an individual stone at rest on the surface of the slope. As the coefficient of friction in static equilibrium they take the tangent of the angle of internal friction of the stony material, measured by shear instruments or devices involving triaxial compression. We shall show that this approach is physically unsound. In particular, this is revealed by the fact that the formulas lead to imaginary values if the angle of internal friction is equal to the angle of repose. However, the angle of internal friction cannot be replaced by any coefficient of surface friction without changing the mathematical structure of Mononobe's formula and its variants. Thus we have to develop a new, physically sounder method of calculating the seismic stability of an embankment slope made of local (coarse detrital) materials. Such a method might be based on d'Alembert's principle. In this we do not consider static equilibrium (rest), but motion of single stones, or of a short, thin layer of material down the slope; account is taken of the residual deformation of the material composing the dam slope. As we see from Ambraseis's report to the Second International Conference on Seismic Construction [2], we can classify such residual deformations as weak signs of seismic action, not endangering the structures of a whole. Such damage can be repaired during routine maintenance. Here we must mention that the principle of considering residual deformations in assessing the strength of a structure is not new; in particular, for dams made of local materials it was apparently first used by Prof. G. I. Pokrovskii at the VODGEO Institute in 1941 in his studies of the seismic stability of the Ortotok gravel dam. In the recently published method of Prof. A. P. Sinitsyn [3], residual deformation is already the main factor considered in designing the dam profile.In practice, the nature of the motion of individual stones (or layers) on the surface of a slope made of stones of a given rock with given mechanical properties is determined by the acting forces and the forces of friction in the plane of motion. In our case, on the basis of d'Alembert's principle [4], for the action of gravity, friction, and seismic acceleration, with allowance for inertial forces (but disregarding air resistance), we can write down an equation for the motion at any time (see Fig. i):where F = P sin O is the component of the body's ...
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