Convergence Modeling Based on a Historical Underground Salt Chamber Example

The monitoring of the process of converging historic mining excavations in the medieval and still-active Bochnia Salt Mine, conducted for years using classic geodetic measurements, allows for determining the results of point displacements. The movements of the selected fragments of the excavation over time, determined on the basis of these displacements, allow for estimating the displacement field, characterizing the entire excavation together with the often-complicated surface layout of the sidewalls, roof and floor. However, this is a certain simplification of the model of this field, and so far, no stress field has been determined that would characterize the compressive forces and would correspond to the characteristics of the measured deformations. This issue has both scientific and practical importance. The latter involves determining the model characteristics of deformations that would be used in the strategy of the conducted protective works. The authors concluded that in modeling displacements, the results of classic geodetic measurements are insufficient for a precise description of the displacement field and reliable simulations of the stress field model. The use of a laser scanner made it possible to obtain an appropriate image of the geometry of the selected excavation and displacements over time. From a scientific point of view, it is interesting to explain the differentiation of displacements in different directions, and determine the nature and share of the acting compressive forces (gravitational forces, the impact of other excavations, tectonic forces).