| Abstract: | Earth dams are constructed on a wide scale for hydrotechnical and reclamative purposes. However, the great water permeability of soils and their bad gradation are frequently responsible for the development of mechanical suffusion and other phenomena resulting in dam destruction. Geophysical observations allow under certain conditions to forecast the development of adverse factors. They thus are, as practice shows, an important tool to observe the technical status of dams. The difference in propagation velocities of elastic waves in the zone of aeration and full saturation determines the applicability of the reflected wave method for determining the depth of seepage flow in the dam supporting mass. This can be also achieved by electrical sounding and induced polarization methods since the resistivity and polarizability of air-dry and water-saturated grounds differ considerably. Maps of equal potentials measured on the dam slope reflect the configuration of the contours of water table of the water flow passing through the dam. This makes it possible to obtain data on the direction and intensity of flow as well as on the presence of heterogeneous grounds filling the dam supporting mass. Besides, regime observations conducted according to the SP method allow to forecast the development of suffusion and observe the redeposition of grounds. If the SP anomalies do not increase with time, the suffusion processes can be regarded as fading out. Enhanced amplitude and increasing areas of anomalies show the intensification of these processes. Combined application of some of the above mentioned methods allowed to obtain many practical results on a number of dams in Transcaucasia and Central Asia. The true position of the depression surface determined in the dam of one of the high-mountain water reservoirs, for instance, considerably differed from the designed one. The configuration of the seepage flow surface and its fluctuation caused by the rise and drop of the water level in the reservoir have been studied in detail on another dam situated on a plain. The sites of the most intensive outwash of fine material have also been located and the processes of soil redeposition in the dam supporting mass characterized. The data of the geophysical investigations were used to plan hydroinsulation and repair work. |
