The foundation of the Zhiguli Hydroelectric Station consists mostly of poli-mineral clays, with montmorillonite prevailing. Montmorillonite composition of clay bond and its base exchange capacity have become the subject of the Zhiguli Hydroelectric Station foundation special analysis. The paper presents the results of the foundation soil investigation conducted during the whole period of the Zhiguli Hydroelectric Station operating life. The change in hydrochemical conditions in foundation contact area of the station is taken into account. The authors analyze two main streams of research: that of physical and mechanical properties of soils conducted according the traditional methodology and that of mineralogical properties of soils carried out according new special methods. According to the obtained data the authors estimate the existing soils condition and make a forecast of soils further behaviour in the Zhiguli Hydroelectric Station foundation contact area.