To protect the city of Alma-Ata from mud-laden flows arising in the basin of the River Malaya Almaatinka (the city is located on its alluvial fan), a dam was designed by the Kazakhsk Branch of Gidroproekt (the S. Ya. Zhuk All-Union Planning and Scientific Research Institute). The site selected is in the middle reach of the river, in a narrow mountain canyon with a width of 60 m in its downstream section. The solid component of the mud flows must be retained in the mud-retention reservoir formed by the dam, and it is planned that the liquid component of the mud and the natural flows of the river be carried through inclined water intakes covered by gratings and a spillway tunnel located in the left bank.The mud flows formed at the time of intensive melting of ice and cloudbursts (July and August) are the most substantial and hazardous. As it is inadmissible to pass mud flows over the incomplete rockfill dam, the principal work of building the dam and necessary mud-retention reservoir capacity must be completed between the periods of mud flow.The Kazakhsk Branch of Gidroproekt considered the alternatives of a concrete dam and a rockfill darn built by the conventional mechanized methods. However, these alternatives were not adopted because of time limitations.Taking the stated circumstances and local conditions into account, the placing of the principal volume of fill in the body of the dam ( Fig. 1 and 2) was planned and executed by blasting the banks with two massive directional explosions.The charges in the right bank were placed on a level with the bottom of the valley, and in the left bank, on a level with the projected dam crest (Fig. 3, and Fig. 1 of the paper by A. N. Romanov and V. V. Garnov in this issue). The location of the right bank charges did not seem to be rational, as the blast increased the width of the valley. However, this location was adopted in the design for a number of reasons. As the results of the first (right bank) blast depended on a number of unexplored factors, which were difficult to evaluate and calculate (cracking, large magnitude of line of least resistance, of the principal charge, and others), the possibility was anticipated that the results would diverge from the plan. Therefore, the second (left bank) blast was not conducted simultaneously with that in the right bank, but five months later. By this time the experience of the first blast had been studied and the plan for the second corrected, as a resuk of which supplementary drift work had to be carried out in the charge chamber.The design volume of the dam embankment was 3.6 million m 3, and the design height 113 m, which figure for the crest takes into account a settlement of 5 m. It was intended that about 80% of the volume in the dam body be placed by directional blasting (right bank, 1.84 million m s, and left bank, 1.0 million), and the remaining volume be completed by machinery.As a result of the right bank blast an embankment height of 62 m was attained, a base width of 560 m, and a crest width of 70 m. The right bank bl...
The basin of the Malaya Almaatlnka River is located in one of the most active mudflow regions of the USSR. In the high-mountaln part of the basin mudflows of local Character are formed almost annually. Disastrous mudflows occur as a result of cloudbursts and outbreaks of morainal lakes during rapid melting of glaciers. They occur considerably more rarely (recorded in 1888, 1889, 1921, 1956, and 1973), but inflict great damage on the economy.To retain the mudflows formed in the greater part of the basin of the M. Almaatlnka River it was decided in 1964 to construct a mudflow-control dam at Medeo. Construction was by the method of directed massive blasting with subsequent additional rock filling to the design profile. The height of the dam is 115 m, crest width 20 m, gradient of the upstream slope from 1:1.6 to 1:2.2 and of the downstream 1:2. A loam facing with an impervious blanket was placed along the upstream slope. The total volume of fill was 3.8 million m 3.The dam project called for a discharge tunnel calculated for a discharge of 30 mS/sec with right-and left-bank intakes. The design of the first provided a discharge from elevations up to 1830 m, the second provided discharge from any elevation in the storage basin. An open emergency mud spillway with a discharge capacity of 230 mS/sec was provided for use in the event of overfilling of the mud storage.The construction work on the dam was completed in 1972, the discharge tunnel was ready by the time of the first directed blast in October 1966, and withstood the dynamic impact of the blast waves well. For a number of reasons construction of the main left-bank water intake and emergency mud spillway was not completed by the time of passage of the mudflow that formed on July 15, 1973.The temporary channel and right-bank intake and the dam'as a whole withstood the power of the mud-stone flow that moved toward the city at a velocity in the order of i0 m/sec --the mud-storage dam held it all. The mud-storage basin was filled to elevation 1835.5 m, i.e., to a depth of 60-70 m, with a total volume of mud of 4 million m s. This was about 2-3 times greater than the 1921 mudflow, which, having reached the streets of the city, caused great damage and loss of llfe. The dam at Medeo prevented a disaster of a considerably greater scale, if one considers the unprecedented magnitude of the mudflow and denser present-day development of the city. The mudflow was retained, but it plugged the inlets to the discharge tunnel. The water level began to rise and the serious threat of reservoir overfilling appeared.To keep the residual reservoir volume left after accumulating the mudflow (2 million m 3) from being filled by the natural streamflow, it was decided to pump out the water. This de---
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