This paper presents a complex study of anhydrite interbeds influence on the cavern stability in the Mechelinki salt deposit. The impact of interbeds on the cavern shape and the stress concentrations were also considered. The stability analysis was based on the 3D numerical modelling. Numerical simulations were performed with use of the Finite Difference Method (FDM) and the FLAC3D v. 6.00 software. The numerical model in a cuboidal shape and the following dimensions: length 1400, width 1400, height 1400 m, comprised the part of the Mechelinki salt deposit. Three (K-6, K-8, K-9) caverns were projected inside this model. The mesh of the numerical model contained about 15 million tetrahedral elements. The occurrence of anhydrite interbeds within the rock salt beds had contributed to the reduction in a diameter and irregular shape of the analysed caverns. The results of the 3D numerical modelling had indicated that the contact area between the rock salt beds and the anhydrite interbeds is likely to the occurrence of displacements. Irregularities in a shape of the analysed caverns are prone to the stress concentration. However, the stability of the analysed caverns are not expected to be affected in the assumed operation conditions and time period (9.5 years).

The design of new investments with underground floors in the downtown urban fabric calls for determining its impact on existing, often historic, neighboring facilities. The article presents the results of own research on 3D spatial arrangement numerical modeling of this type of investment. The scope of the research includes the analysis of neighboring buildings (including historic buildings), construction of the 3D numerical model, and calibration of the subsoil model taking into account the actual results of geodetic measurements. Own research as well as the completed housing development complex in Poland, downtown Warsaw, including data from project design and implementation documentation serve as the basis for research and analysis. As a result of said research and analysis, it was found that 3D computational models allow mapping of actual impacts within the designed new buildings and neighboring buildings, and as consequence - after appropriate calibration - a good reflection of soil displacements in the area of the planned investment. The knowledge of the anticipated values of soil displacements related to erecting new buildings is necessary at the design and implementation stages to ensure safety in all phases of works of existing buildings.