Use of chlorides in construction of the Serebryansk hydroelectric station-1 earth dam

Abstract

During construction of the Serebryansk hydroelectric station-1 dam, the most labor-consuming operations were those required for construction of the impermeable part-the core of sandy loam moraine soft [1]. Most of the core (90~ was constructed by dumping soil into pools of water; the remaining volume (the narrow upper part) was placed by dumping soil of natural water content in layers. Both methods are "wet" processes and, therefore, the effect of low temperatures on the course of the operations is quite considerable, and placing the soft in the core in the winter was impossible without taking special measures. Among these was the use of chlorides for the following purposes: for summer preparation of the unfrozen borrow for dumping in the structure in the winter; b) for preparation of the foundations and surface in the winter for the dumped fill; c) for combatting freezing of the soil in the dump trucks and excavator buckets.The method of dumping soft into pools has proved itself at many hydro developments on the Kola Peninsula, both by the simplicity of the technology and the high quality of the embankment obu3ined [2, 3]. Under summer conditions the pools were constructed with a depth of 2-2.5 m, a width equal to the width of the core, and length to 400 m. Blankets of 2-3-m-thick soil constructed on the slopes of the previously dumped upstream and downstream transitional layers of the dam served as the embankment for the pools in a longitudinal direction and drydumped transverse dikes in the transverse direction. After filling the pool with soil the dikes were removed, since theirsoil was considered to be of inferior quality.Dumping of the soil into the pools, with a number of changes in the technology of the operations, was adopted by the builders also for constructing the dam core during the winter. Winter dumping differed by an increase of the depth of the pools, construction of the core in strips along the transitional layers, and delivery of heated water to the pools, which permitted year-round operation at almost the same rate [4]. However. during the first winter season serious difficulties arose because of freezing of the dry-dumped embankments; the longitudinal blankets, which froze during pool preparation, thawed as the pool was filled with warm water and flattened out in the underwater part, remaining above the water in the form of frozen "bars'. As a result leaks formed in the blankets, which sometimes were so appreciable that it was impossible to raise the water in the pool to the necessary level. "the embankment transverse dikes did not leak owing to their greater thickness and better compaction, but their removal required preliminary loosening by drilling and blasting.Using the first winter season experience of core construction, by the second season the builders introduced modifications into the technology of operations, one of which was making the embankments of salted nonfreezing soft which eliminated the difficulties. There were no leaks in blankets of such soil, since on filling the pool fla...