The complex of structures of the Sayano-Shushenskoe and Maina hydroelectric stations on the Enisei River has a total volume of concrete of about i0 million m 3. The aggregates for the concrete are prepared by sorting a sand-gravel mixture at the gravel-sorting plant (GSP) located 40 km from the site. The quarry, representing ancient deposits of the Enisei River, is located 2 km from the GSP and the deposits are characterized by a variable particle-size distribution of the material in different sections~In this case, sections of sands with a fineness modulus Mf from 1.4 to 2.9 and in lenses from 1.0 to 3.1 (sometimes more) are found.In the initial stage of construction selective excavation of the quarry was accomplished, but with an increase in the rate of concreting and working of the quarry it was necessary to use all sections, including with finer sands. An analysis of sands obtained from different sections of the quarry showed that each section of the quarry has an average size of the sand, in which case the deviations of particular samples, as a rule, do not exceed • unit of the fineness modulus (Fig. i).The available instruments do not permit a prompt particle-size analysis of the sand during its delivery to the mixers.Investigations of the characteristics of sand over a long time showed a stable relation between Mf, weighted average graindiameter, and specific surface of sand for the entire deposit (Fig. 2). A Stable relation is absent between Mf and the volume of voids of sand, although there is a tendency toward an increase of the volume of voids with decrease of Mf. To obtain the indicated relations between Mf and the specific surface and weighted average diameter of the grains, several dozen sand samples taken in different years of construction from different sections of the quarry were analyzed.The specific surface of the sand was determined by the known formula Ssp= (16,5K/lOOO)(o+2b+4c+8d+16e+32f),(i) where a, b, c, d, e, f are particular residues smaller than 2.5 mm on the sieves and on the tray; K is a coefficient taking into account the grain shape (in the given case taken equal to 1.5).The adopted technological scheme of the gravel-sorting facilities does not permit averaging the sand by size due to such large time intervals which would permit considerable smoothing of the variations of size during excavation of different sections of the quarry.The original selection of the compositions of the hydrotechnical concretes was performed by the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) with sands with Mf = 2.3-2.5. The production compositions of the concrete, corrected by the construction laboratory on the basis of the compositions and with the participation of VNIIG, were used for several years, were perfected, and had a comparatively low content of cement (Table 1 for Mf = 2.0-2.4), Beginning in 1979 a decrease in the size of the sands being used at first to Mf = 1.8 and then to Mf = 1.4-1.6 with considerable variations was observed, since different secti...
Electrometric control of the relative density of the concrete mix is based on measuring its electrical parameters, which are related directly to its density. This method, which was first used successfully in the construction of the Dnepr hydroelectric station dam [i], was subsequently used on the Toktogul, Ingurl, and other hydrostatlon projects. However, for the wide industrial use of electrometrlc compaction control a more detailed check of individual problems of the method of its use was required.First of all, the design of electrode-sensors placed in the concrete mix was developed. Single-electrode spear-sensors and double-electrode probe-sensors submerged in the concrete and electrodes left in the concrete mix ~Ig. i) were used in the work. The operating principle of all types of sensors is based on the principle that when an alternating current is supplied to them an electric field is created in the concrete mix whose strength (for constant parameters of the current and composition of the medium) depends on the density of the concrete [2]. Since the electric field potential in the medium decreases with distance from the current source, it was necessary to estimate the zone of action of the sensors and parameters of the electric current, The investigations were carried out under laboratory conditions and directly in the concrete blocks.In the laboratory experiments we used a homogeneous medium (water) and plastic mortar, which were placed in a Plexiglas mold equipped with a probe connected to the measuring instrument, A dielectric plate slmulating nonconducting inclusions, having an area 3-4 times greater than the area of the probe electrodes, was introduced into the mold. The distance between the plate and probe was changed, the resistance of the medium being measured at each position.
Tests of cores drilled from various depths in zones of concrete dam blocks and special investigations of the strength of large concrete cylindrical specimens performed at the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) and abroad [1, 2] showed that the strength of concrete varies over the height, increasing from the top toward the bottom of the layer. Figure 1 shows the function Rh/R o = f(h), where Rh/R o is the ratio of the strength of the layer at distance h from the top of the layer of concreting to the strength of the concrete of the upper zone of the layer of concreting.An analysis of the strength of cores with a diameter of 15 cm and height of 30 cm drilled from concrete blocks of the Sayano-Shushenskoe hydrostation showed that Rh/R o ffi 1.18 for a layer height of about 600 ram. Thus a multilayer concrete block represents an alternation of weak and strong zones of concreting.Investigations of models of a block being concreted on specimens with a transverse size of 100, 200, and 300 mm consisting of layers differing in strength showed that the average strength of concrete of multilayer specimens consisting of layers of various strength is higher than the strength of the weakest layer R w and lower than the strength of the strongest layer R', and the standard deviation of the strength of multilayer specimens is less than the standard deviation of the strength of single-layer specimens.An analysis of the stress--strain state of models of a block showed that weaker and more deformable layers and zones of layers of concreting (w) are confined by stronger and more rigid ones (s), and vice versa; the stronger and more rigid layers and regions of the layers of concreting acquire additional transverse strains 9 as a consequence of the effect of the more deformable layers of low strength (Fig. 2).An increase of the average strength and decrease of the standard deviation of the block selected in the form of a prism with a ratio of the height to the width H/B = 4 depends on the number of layers in the model. Thus, if the layer of concrete is characterized by two regions: an upper weaker region (R w) and lower stronger region (R s) with heights t w = t s = tlffi/2, where t]a is the thickness of the layer, then the ratio tw/B will determine the number of layers of concrete in the model and, consequently, the massiveness of the model of the block.The strength of a model of a block with three regions S, W, S is determined by the expression [3] R'b I =R~W-i-{[ ( R : -}-Rt-~S) /2]--R, w'}K:in ,where Ri s, Ri w, Ri_l s, R bl are respectively the strength of the strong and weak region of the i layer of concreting, strong region of the i layer of concreting, and model of the block; Kin is the coefficient of influence of the strength, determiner experimentally.The values of Kin as a function of tw/8 are given in Fig. 3 for a three-layer specimen for t, 9 t w with a middle less strong region. The average value of the strength of the block is obtained by substituting into expression (...
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