624.131.7 The rock---earth dam of the Hoabinh hydraulic development, with a central core of clay-skeleton soils, threelayer transition zones of gravelly-sandy soils and fine rock mass, and shells of rock mass, is 125 m high and has a total fill volume of 21.35 million m 3. For the dam fill placement use was made of five deposits of cohesive soils with a total reserve of 2.5 million m 3 (the requirement was 1.75 million m3), three deposits of rock with a total reserve of 16.1 million m s (requirement, 14175 million mS), and three deposits of sandy and gravelly soils with a total reserve of 8.4 million m s (requirement, 4.85 million mS).Deposits of Cohesive Soils. At the construction site, two genotypes of cohesive soils were established: detrital-deluvial for the dam core fills and alluvial for the injection work. The deposits of detrital--deluvial origin are developed everywhere and occur primarily in the watershed slopes of the valley. These deposits contain rock having different compositions, characterized by a sharply variable morphology and by its quality as useful mass. The clayey part of the soil is basically represented by kaolinite with hydrated mica mix. In accordance with the current classification (GOST 25100-82), the soils correspond to the category of sandy loams, ordinary loams, and clays. The content of large-fragment fractions (over 5 mm in diameter) in these soils varied from 5 to 80%. The physical characteristics of the cohesive soils for the different deposits are presented in Table l, and the grain-size distribution in Fig. 1. The deposits are located in slopes with a steepness of 10 to 30 ~ the thickness of the cover soil (vegetable layer) ranged from 0.5 to 4 m, and the thickness of the detrital---deluvial zone varied from 5 to 20 m. The lower limit of the deposit is uneven, and at some places it drops forming pockets in the unweathered rock zone.Among the explored deposits of the second genotype, namely the alluvial, deposit No. 16 was exploited. This deposit is located on the right-side bank of the Da River, at the downstream side of the hydraulic development, and corresponds to above-floodplain terrace 1. The mass has a useful thickness of 9--12 m and consists of alluvial loams .and clays which are heavily watered. The deposit soils were used for preparing injection grouts.Deposits of Gravelly-Sandy Soils (GSS). The GSS used for the dam transition-zone fills and for concrete aggregate preparation were excavated at deposits located in the Da River channel: one of them at the upstream side (No. 46) and two at the downstream side (Nos. 7 and 7a). The useful thickness of the deposits has a two-layer morphology. At the top there are fine sands in an 8--16 m thick mass, which is underlain by sandy-gravelly formations with sand filler. The mineral is underlain by native material of the rock and semi-rock types. The deposit limits are the banks, covered by sandy and ordinary loams. The river depth in the quarry zone varies from 3 to 8 m. The material is made up of oval particles consisting of...