More on the landslide at Mingechaurskoe Reservoir

Abstract

The deformations of the right-bank slope that have occurred in the vicinity of the AzSREGS and Verkhne-Karabakh Irrigation Canal (VKC) intakes have already been described in this journal [1]. The Verkhne-Karabakh Canal supplies water to irrigated lands in the republic, and the AzSREGS, with a capacity of three million kW, is the largest generating facility of the Transcaucasus. Landslides have long been known to occur on the right-bank slope of the Kura Valley, in the vicinity of the Mingechaur Gap. They gave rise to concern regarding the ability of a planned dam to survive, and a detailed study of these and other physical-geological processes leading to deformation of the slope was therefore carried out over several decades. Preliminary plans for construction of a dam 7-8 m high in the Mingechaur Gap were begun in 1915. In 1925, a scientific commission established to survey water resources in Azerbaidzhan raised the question of building a large reservoir with a dam 20-25 m high at the site. Exploratory studies made in 1926 enabled geologists to conclude that construction of a high dam could not be recommended, because of the complex geological conditions (low-strength, easily weathered porous gypsiferous rocks, and extensive "clay karst" bordering the valley, and land slippage). As a result of the exceptionally favorable location of the gap tbr irrigation of large areas and the possibility of cheap electric power, it was decided to make a more thorough geological study, which was carried out in 1927-1928 by the geologist V. A. Strakhov. His report pointed out that engineering-geological conditions would permit construction of a high dam, were the various geological features to be fully taken into consideration. The Administration for Water Resources Utilization in the Kura-Araksin Basin (Zakvodproiz) completed a draft plan for a Mingechaur Dam 38 m high in 1930. The engineering specifications adopted by the Zakvodproiz in 1931 set the dam height at 64 m. Preliminary work was continued in 1932-1934. Special attention was paid to the tectonics of the rock mass and the com~ection between it and the "clay karst." These studies confirmed that a high dana could be built in the Mingechaur Basin. A 1938 request for proposals provided for a dam 66 m high. The height of the dam finally built was 80 m. The main cause of landslides in the area under natural conditions was undercutting by the river of the clay and sandstone strata, which dipped toward the riverbed [2]. Smaller slides occurred on the sides of gullies. The topography was complicated in places by pits, sinkholes, and other manifestations of the so-called "clay karst," which were considered to be of decisive significance in assessing slope stability. However, it was found during the initial stages of research on the engineering-geological conditions for construction of the Mingechaur Dam that the "clay karst" encompassed only the zone of active weathering and was nowhere detected below 20 m from the surface in the unnaodified country rock. The main factor responsible for its creation was mechanical erosion of the weathered rocks by the water in temporary streams that penetrated the rock in concentrated flows along cracks. Leaching out of water-soluble salts, which were originally considered to be the main factor responsible for development of the "clay karst," apparently facilitated this process but played a subordinate role, since the gypsum content in the weathering zone did not exceed 2-3 %. The salinity of the country rock was even lower. It