Salt caverns are an attractive solution to the growing energy demand in view of their large storage capacity, safety of storage operation and long operation time. The designing process of salt caverns is still considered a complex issue despite progress in geotechnical, construction and exploration methods. Finding the optimal shape and dimensions of a salt cavern in given geological conditions is a difficult engineering problem in view of safety and stability requirements. In this paper, the stability of typical cavern shapes (cylindrical, enlarged top, and enlarged bottom), with each of the three variants differing by their diameter, was evaluated against the stability factors of the geological conditions of the bedded salt deposit. Moreover, the analysed shapes were examined in terms of edges. The three-step smoothing of sharp edges was performed, and its impact on the cavern’s stability performance was studied. Moreover, the analysis aimed to find the optimal cavern shape and volume in the implemented geological conditions. The evaluation was based on the following criteria: the displacement, effective strain, von Mises stress, strength/stress ratio and safety factor. The results of this evaluation can be useful in the design of an optimal cavern shape and volume and for planning new cavern fields for storing natural gas, compressed air or hydrogen in the bedded salt deposits.

Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.

Located in central Poland, the Kłodawa salt dome is 26 km long and about 2 km wide. Exploitation of the dome started in 1956, currently rock salt extraction is carried out in 7 mining fields and the 12 mining levels at the depth from 322 to 625 meters below sea level (m.b.s.l.). It is planned to maintain the mining activity till 2052 and extend rock salt extraction to deeper levels. The dome is characterised by complex geological structure resulted from halokinetic and tectonic processes.Projection of the 3D numerical analysis took into account the following factors: mine working distribution within the Kłodawa mine (about 1000 rooms, 350 km of galleries), complex geological structure of the salt dome, complicated structure and geometry of mine workings and distinction in rocks mechanical properties e.g. rock salt and anhydrite. Analysis of past mine workings deformation and prediction of future rock mass behaviour was divided into four stages: building of the 3D model (state of mine workings in year 2014), model extension of the future mine workings planned for extraction in years 2015-2052, the 3D model calibration and stability analysis of all mine workings.The 3D numerical model of Kłodawa salt mine included extracted and planned mine workings in 7 mining fields and 14 mining levels (about 2000 mine workings). The dimensions of the model were 4200 m × 4700 m × 1200 m what was simulated by 33 million elements. The 3D model was calibrated on the grounds of convergence measurements and laboratory tests. Stability assessment of mine workings was based on analysis of the strength/stress ratio and vertical stress. The strength/stress ratio analysis enabled to indicate endangered area in mine workings and can be defined as the factor of safety. Mine workings in state close to collapse are indicated by the strength/stress ratio equals 1. Analysis of the vertical stress in mine workings produced the estimation of current state of stress in comparison to initial (pre-mining) conditions.The long-term deformation analysis of the Kłodawa salt mine for year 2014 revealed that stability conditions were fulfilled. Local disturbances indicated in the numerical analysis were connected with high chambers included in the mining field no 1 and complex geological structure in the vicinity of mine workings located in the mining fields no 2 and 3. Moreover, numerical simulations that projected the future extraction progress (till year 2052) showed positive performance. Local weakness zones in the mining field no 7 are associated with occurrence of carnallite layers and intensive mining which are planned in the mining field no 6 at the end of rock salt extraction.

Effective planning of the cavern field involves determining the optimal pillar width between the caverns and the feasible number of caverns based on geological and mining conditions. The proper design of the pillar width is crucial to ensure the stability of the cavern field and the rational utilization of the rock salt deposit. The stability of the pillars is a complex problem influenced by various factors, including rock salt creep, changes in the cavern pressure during operational cycles, mechanical parameters, and failure criteria of the rock salt. To address this problem, the stability of the cavern field in relation to the number of caverns and pillar widths is evaluated. The evaluation is based on the following criteria: displacements, von Mises stress, strength/stress ratio, and safety factor. Three variations of pillar width and three variants of cavern fields, differing in the number of caverns, are considered. Results show that the allowable pillar width is affected by the number of caverns in the cavern field. Moreover, the stability analysis reveals uneven stress and deformation distribution in the cavern field. When the pillar width is 2.0–3.0 times the diameter of a cavern, pillars at the centre exhibit poorer stability than those at the edges of the cavern field. However, with a narrower pillar width, the highest displacements occur at the field's edges. The findings of this study provide a valuable date in the planning, design, and operation of new cavern fields for the underground storage of energy sources such as oil, natural gas, hydrogen, and compressed air in rock salt deposits.