Mining and processing of the mineral resources of Estonia may sharply disturb the environment. The underground mining of the Maardu granite deposit may have a significant impact on the groundwater resources if the resultant caverns are unstable. On the positive side, it is possible to use the caverns for storage of crude oil, gas and petroleum products, for storage of radioactive waste or the waste products of Tallinn. This process is safe and does not harm the environment. The shape and the dimension criteria were evaluated by numerical modelling This paper presents the results of a study based on a two-dimensional explicit finite difference modelling (FLAC) of the rock mass. Since little field information was available, the rock mass parameters are estimated from geological data, using Bieniawski＇s rock mass rating (RMR). All the calculations ale performed for single and multiple caverns. The resulting rock mass responses are presented in terms of induced deformation and stresses. The results indicate that for the single and multiple caverns, even with different cavern shapes, there are no significant differences in the stability situation. A continuous rock mass approach does not seem to give adequate results and it is recommended that a discontinuous rock mass approach be used in future analyses.