Construction of a dam in the permafrost zone

Abstract

The dam on the River Irelyakh [1] is the first in hydraulic engineering practice to have been built on weak ground permanently frozen to an ice content 60%. The maximumheight of the dam is 20 m and the crest length is 320 m. The reservoir the dam has created serves chiefly as a water supply. Construction of the dam was started in 1961, and the reservoir was filled to designed levels in the flOod of 1964. The climate in the area of the dam is markedly continental, with an average annual air temperature of-8.2~The dam rests on Quaternary rocks (sandy loams, loamy sands and sands) all permanently frozen to an ice content 60%. The bedrock is marl, marly clay, limestone and sandstone frozen to 10%. Permafrost extends to a depth of 300 m.The dam (Fig. 1) was erected from loamy sands and sandy soils without drainage or filters. Filtration is prevented in the dam by means of a frozen skirt created by artificially freezing the center of the dam. To preserve frozen conditions at the b'ase of the dam, the erection operations were carried out in the following order.Peaty, plant-detrital, and muddy softs were removed from the entire area of the dam base. The foundation yeas cleaned up in the autumn of 1961, so that it could acquire the lowest possible temperature in the winter of 1961/62. In the channel, where the foundation was composed of rewashed gravel and sand beds, the latter were removed so as to prevent filtration through them during the establishment of the frozen skirt.To reduce water filtration due to possible thawing of the frozen ground during operations, a key was construtted which cut down through the overlying frozen Quaternary rocks to the bedrock. Before the floodwater of 1963 was admitted, loamy sand was laid in the trench under the key. In the spring, soil was laid in the dam foundation, on a specially frozen base.The body of the dam was built up in summer and autumn after the summer floods had passed (Fig. 2). Summer waters were passed through holes in the dam. In autumn and winter the dishcarge was pumped over the dam. The dam was constructed of thawed ground of 12-18% moisture; the moisture content was allowed to rise only to 35% when laying the soil in the key in the channel part of the dam, and to 23% when filling in the holes. To obtain ground with this percentage of moisture, it had to be dried to its proper moisture content in the quarried state was 40-45%. The ground was dried in the ribs of the quarry, and also at the deposition sites at the dam. The temperature of the ground laid on the dam was between 0 and 16"C (Fig. 2).