Finland is the home of many hydroelectric power stations. Most of them were built during the three decades starting from the 1950s and ending in the 1970s. To make a hydroelectric power station efficient, one has to create optimal circumstances. That means building dams to regulate the water flow. Most of the Finnish dams use earth-fill.

First part of this thesis includes the responsibilities of the dam`s owner. Dam`s owner has to make sure that everything is done according to the law. In case of an accident the owner is always the responsible party, if something has been over looked in maintenance of the dam.

The second part explains the parts of common earth-filled dam and how those parts work. After that the most common research techniques are catalogued and explained.

The last part consists of two new research techniques. These two techniques are used in other countries but not in Finland. In the case of the Flat Dilatometer it was clear that it did not work in researching the Finnish earth-filled dams. The other, Sonic Drilling Method, on the other hand seemed very promising. The conclusion was, that it would give better results in the research compared to methods that are used nowadays.