Placement of alluvial sands in the channel dam of the Tyuyamuyun hydro development

Abstract

A channel dam should be made from alluvial sand excavated directly in the river channel. Dam height 30 m, slope of faces 1:4, volume of fill about 1 million m 3.It was originally proposed to construct the dam by the hydraulicking method. For this purpose two stockpiles were hydraulically filled on the right bank of the river. Before hydraulic filling of the stockpiles a part of the No. 1 embankment (from distance mark DM 0+00 to DM 7+00) immediately adjacent to the channel dam was hydraulically filled. Hydraulic filling was carried out alsofrom a channel borrow pit. The experience of hydraulic filling of the embankment showed that the placement of soil by such a method (according to the geotechnical control data) is carried out with a comparatively low unit weight, equal to 1.40-1.45 g/cm a (with 90% probability).During designing, in connection with the Gazli earthquake, the design seismic intensity of the region of construction was increased to 9.A characteristic of water-saturated sands is their ability to pass into a liquified state under certain dynamic (seismic) actions. A number of cases of the failure of hydraulic-fill dams under construction or already constructed from various dynamic loads (traffic along the dam crest, earthquakes, etc.) are known in world dam construction practice. Investigations established that with an increase of placement density, soil size, and intensity of applying a vertical load, the stability of saturated sands increases.In connection with this, to estimate the dynamic stability of a channel dam special laboratory investigations were performed [i].The results of the investigations showed that sand should be compacted to 1.52-1.55 g/cm 3 with degree of desnity D ~ 0.75. To keep the hydraulicking method of constructing the dam, it was necessary to place a special surcharge on the slopes with a thickness of more than 2.0 m (stone, gravel, or concrete). Under conditions of the region of construction these materials were scarce and costly. Therefore, field investigations were organized at the construction site of the hydro development on experimental embankments with layer-by-layer placement of sand with rolling.