The Interaction Principle in the Assessment of Pillars’ Secondary Stress-Deformation State

In the field of mining, one of the exploitation methods that is still the most used in rock salt, potassium, and magnesium salt deposits is the method with the room and abandoned pillar. The salt mining method with rooms and pillars represents a unique spatial system for which the establishment of an optimal correlation between the parameters of the room, pillar, and rock massif is required in any given situation. Thus, the dimensioning of the most requested element in the system is followed, and depending on its parameters, the other parameters of the system are established. Considering the exploitation method with rooms and pillars, the pillars are certainly the elements that are subjected to the greatest loads. In the situation where the deep exploitation of salt is done with square pillars, the evaluation of the optimal parameters of the elements of the exploitation system requires: establishing the loads that appear in the surrounding salt massif (the natural stress state); the qualitative-quantitative determination of the way of distribution of the secondary stress state in the pillars; evaluating the bearing capacity of the pillars; and establishing their geometric elements. Solving this problem can be achieved by different methods: based on the theory of limit equilibrium, taking into account the effective stress in the pillars; methods of the mechanics of the continuous system based on the analytical models for evaluating the secondary stress and deformation state of pillars and floors; and numerical methods combined with the results and measurements from the laboratory and in situ tests. A methodology based on the pillar–room–salt massif interaction principle was proposed for the analytically achievable stability exploitation system of rock salt by the dry method as the depth increased. Applying this method, the secondary stress-deformation state in the pillar can be established by taking into account the rheological behaviour of the salt, changing the pillar shape, and the extraction technology. The presented algorithm can be extended in the field of exploitation, where the room and pillar exploitation methods are used.