On-slte investigations of seepage in the foundations of dams are one of the most important methods of monitoring the state of the foundation and behavior of the structures. On the basis of the character of seepage and its development during filling of the reservoir one can Judge the permeability of the./rocks, presence of seepage-defomatlon phenomena, effectlveness of the underground contour and cutoff and stability of their operation, and state of stress and strain and its change with time. On-slte investigations of seepage are especially necessary for hlgh-head dams, in the foundations of which large stresses occur and nonuniform deformations are possible.The foundation for the dam of the Ingurl hydroelectric station [I] is composed of llmestones, dolomltlzed limestones, and dolomites. The rocks are characterized by increased or severe Jolnti~.The Joints, as a rule, are filled with clay, loam, and grus. Within the active seepage zone there are a number of large tectonic fractures (Nos. 8, 15, 15a, 16, 19,(51)(52)(53) 616, etc.) and a rlght-bank fault. A number of fractures (Nos. 8, 12, 15, 15, 19, and certain others) have dense clay filling material and a developed system of pinnate fractures. The permeability of the rocks is characterized by a specific inflow to wells on the right bank within 0.15-1.88 llters/min.m s and on the left bank 0.11-0.4 llter/min.m 2. The permeability of the rocks decreases with depth, but it was not possible to reach impervious zones during drilllng of exploratory wells to a depth of 120-150 m.The flow interruption in the dam foundation includes grouting to a depth of 15-20 m, and to a depth to 140 m and length up to 200 m in the banks, and a system of channel end canyon-wall drain wells. The largest fractures, Nos. 8, 16, and 19, and part of the leftbank fault adjacent to the dam are being excavated by the mining method and sealed with concrete. There are six levels of grouting, drainage, and access tunnels in the dam foundation end canyon walls for conducting drilling operations. 0n-slte investigations and observations in the dam foundation were begun by the State All-Unlon Trust for the Stabilization of Foundations and Structures (Gidrospetsproekt) in 1971 and have been carried out continuously since. These investlgatlons can be divided into three periods according to their tasks and nature: the first included excavation of the foundation pit and underground workings of the sixth horizon, the second flooding of the pit, and the third fill~n S the reservoir.The on-slte investigations of seepage durln8 the period of excavation of the underground workings and pumping out the foundation pit were carried out for the purpose of supplementing and refining ~he data from surveys and detailed studies of the permeability of the foundation rocks, using the created conditions of seepage into the pit (head up to 38 m) and variations of the water level in the river in front of the cofferdams. The tasks of the invest~ations included a determination of zones of concentrated and increased seepage...
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