Daugava River is the largest river in Latvia, and it has been developed for hydropower with the construction of dams at three sites namely Plavinas, Kegums and Riga HPP. In the 1960s the largest of the three hydroelectric power plants - Plavinas Power Plant, having a considerably higher head than the other two and a relatively large reservoir, was built up. It is built across an ancient pre-glacial river channel, which is filled with glacial deposits up to 137 m or more thick.

Since construction of the power plant the properties of these soils and their behaviour are tested and discussed. During 2009 drilling and sampling were performed close to the Plavinas Dam as a scope of the geotechnical investigation for construction of the additional spillway on the right side of the power plant. Part of the samples was used for testing of soil clasification and mechanical properties in Geotechnical laboratory of the University of Latvia. Based on the testing results soils were classified and their properties described. Testing results were compared to previous findings and geotechnical properties of the soils tested during construction of dam. The tested soils are similar to the soils under Plavinas dam concrete structures and detail analysis of the soil properties helps to explain the long term behavior of the Plavinas dam structures, the possible changes of the soil properties as a result of the loading and impact of the artesian groundwater pressure.