The idea of building a high-pressure underground storage of natural gas in Reštanj bellow the Gradec Hill, Senovo community (southeastern Slovenia), was initiated in 2004. Normally, high-pressure underground storages of natural gas are built in strong rocks like granite. But research in Sweden has shown that it is also possible to build a high-pressure underground storage in carbonate rocks. In my diploma thesis I simulated the effect of different heights of overburden and of working pressures produced by filling of the planned storage in Senovo. I have modelled displacements, stress field, and have evaluated spalling criteria. Eighteen geomechanical models were designed using boundary element method with numerical program Examine2D (Rocscience). Each produced model uses a different combination of overburden height and working pressure. For each model I evaluated the displacements, stress field, and the stability of the excavation according to the spalling criterion in four checkpoints. In addition to the analyses carried out in this thesis, detailed geographical and geological characteristics of the planned building area are described along with the processes of engineering geological description of rock masses and determination of rock types. Also, three classifications used in rocks are presented. These standard classifications are: RQD (Rock Quality Designation Index), RMR (Rock Mass Rating) and GSI (Geological Strength Index). Analysis results show that the overburden height does not significantly influence the rock response. Much larger is the imapct of working pressure, both in a negative and positive way. From the modeling results the optimal working pressure is in the range from 10 MPa to 15 MPa.