Geomechanical analysis of the rock mass stability in the area of the “Regis” shaft in the “Wieliczka” salt mine

Abstract

The “Regis” shaft is one of the key workings which ensure the safety and smooth flow of tourist traffic in the historic Wieliczka salt mine. Its fault-free operation requires the monitoring of the technical condition of the supports and the surrounding rock mass. The results of the conducted monitoring and macroscopic observations of the lining in the shaft and of the adjacent workings have exhibited gradual and progressive degradation of the rock mass structure. In order to assess the impact of these processes on the shaft and on the nearby workings, a spatial numerical model of the rock mass has been created using the FLAC 3D software. The model geometry was determined after analysing the geological documentation of the area in the form of maps, cross-sections, and on the basis of visitations in the workings located in the vicinity of the shaft. On this basis, it was determined that the behaviour of the “Regis” shaft is primarily affected by a large post-mining chamber (the “Kloski” chamber) located in its immediate vicinity, on the north-eastern side. The tool used for the simulation (FLAC 3D software) allowed for the mapping of the behaviour of the continuous medium and the simulation of the destruction of the material by assigning to it (after reaching the limit stress state) the features of a plastic medium. On the basis of conducted calculations and simulations, it was determined that leaving the rock mass without any protective works may pose a threat to its stability and the stability of the “Regis” shaft lining. To protect the shaft and the rock mass, it was proposed to fill the “Kloski” chamber and the shaft below level IV. Such solution would stop the propagation of damage zones and minimise the rock mass displacement. Creating a stress and deformation state in the model, achieved as a result of backfilling a part of the shaft and the chamber, is highly likely to ensure the stability and safe operation of the workings located above it, in particular the section of the “Regis” shaft from the surface to level IV. The presented example showing, that backfilling used even many years after excavation of chamber can bring good results in terms of improving rock mass stability.