Investigations of the moraine soil in the core of the serebryansk dam

Abstract

UDC 627.824.3.065.001.5 The core of the dam was constructed" by dumping moraine soil into water. The builders successfully solved, in so doin~ the problem of year-round conducting of operations, and the technology of dumping the soil improved constantly. During the summer the dam core was dumped into individual pools with a length of 100-400 m, a width equal to the width of the core at the operating elevation, and height of 3 m. The pools were embanked about their perimeters and filled with water to a depth of 2-2.5 m. The moraine soil was dumped into these ardfical pools. Dumping was done by the "pioneer method" with a wide front and the pools were filled with soil over the entire area. After dumping one layer of the core, pools were created in the same way for dumping the next layer, etc. The thin above-water soil layer (0.5-0.8 m) was compacted by the repeated runs of the dump trucks over it. Unlike the summer technology, during the winter the moraine soil was dumped only as strips with a width of 6-10 m, running along the perimeter. The embankment of the next layer was placed on the dumped strips, the water level was raised 3 m, strips were dumped about the perimeter, etc. A pool with a depth to 12 m was created. Thus, the middle part of the core was always under water and did not freeze. The soil, freezing to a depth of 30-50 cm, thawed rapidly when the water level in the pool was raised by the next 3 m. Elec=ic thermometers embedded in the frozen soil showed that thawing occurred within 5-10 days. The reduction of the usual demands imposed on the material and method of dumping the rock shoulders was due to the design of the dam, which provides, as it were, independent settlement of the shoulders and core with slippingalong thetransitional zones. The high category of the dam and the characteristics of its construction required thorough investigations to evaluate the granulometric composition of the soil in the structure and, in particular, to solve the problem of qualitative substantiation of the winter method of constructing the core. The main indices of the quality of the soil placed in the dam core were: a) dry unit weight of the soil and its fines (fraction smaller than 2 ram); b) relative density and void ratio; c) granulometric composition; d) water impermeability. During construction of theSerebryansk dam about 3000 samples of the moraine soil were taken and tested. For comparability of the quality of the summer and winter dumped fills and for evaluating the degree of inhomogeneity of the core body with respect to density, impermeability, and granulometric composition, the core was conditionally divided in zones I-VII (Fig. 1)depending on the time of placing the soil, and the indicated characteristics were determined for each. The demity characteristics of each of the zones are represented by curves of the distribution of the values of the dry unit weight of the soil and of its fines (Figs. 2 and 3). The average values of the dry unit weight of the core soil corresponding to 75 and 5090 were respectively 2.03 and 2.10 tom/m 3. Void ratios 0.32 and 0.29 correspond to these density values. Analogous values of the dry unit weight of the fines (this index was the criterion in evaluating the quality of placing the soil) were respectively 1.73 and 1.82 tons/m 3 and See the article ofA. I. Liberrnan and M. V. Stankevich published in this issue of the journal.