The explored terrain falls within the central parts of the Rila-Rhodope engineering-geological region which has undergone continuous tectonic evolution. The big fault structures manifested in the region were reflected both on relief modeling and on the engineering geological properties of rocks and soils. The studied site is situated on a steep valley slope, inclined to the east and with an average altitude of 1540 m. The terrain is built of deluvial Quaternary deposits situated on pre-Cambrian gneisses and marbles. The geotechnical exploration carried out has proved that site conditions are complex and require special attention when selecting the foundation pattern. The rock substrate is covered by Quaternary deposits of variable thickness, reaching 20.00 m at some places. The conditions are further complicated by the existing zone of vertical karst forms, filled with soft clay of low strength and deformation parameters. The karstified marbles create the prerequisite of significant water inflow in the construction excavation. Unconventional foundation scheme has been accepted due to the predicted irregular subsidence of the Quaternary soils and the expected high water inflow from the karst massif. In the terrains built of old metamorphic complexes weak and karst zones of considerable thickness are encountered, which are the product of tectonic and weathering processes. Various methods of geotechnical explorations, which will guarantee the detailed elucidation of the geological circumstances, have to be applied in order to establish such zones. This will ensure the correct choice of the foundation pattern.