Geodetic conditions of Warsaw underground extension

The construction of an underground railway system is a very demanding building investment. It requires great concentration of a building potential over an exceptionally vast area. On the one hand, the building site covers a vast densely built-up urban area and on the other, a tunnel is actually excavated over a small space covered by its "front" and interior. The above conditions are extraordinary both because of the technical difficulties of the works to be carried out and high precision required by individual construction elements. Another problem is the disturbance of geotechnical stability of the ground and the ensuing dangers posed for the adjacent buildings. The paper presents all basic elements of geodetic activities connected with the underground construction, from the designing stage up to construction works.