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

Abstract

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.

Stability Analysis of the Exploitation System with Room and Pillar by Analytical Methods

“…In order to characterize the physical state of the salt and its influence on solving the problem of stability and reliability of the geometric elements (pillars, slabs, etc.) of the salt exploitation methods, it is necessary to know the value of the main physical properties, namely: specific gravity, volumetric weight, natural humidity, compactness, and porosity [9,[12][13][14][15]. Importance for the field of geomechanics is the knowledge of the two aspects of the mechanical behavior of rocks, that is, rock strength and rock mass deformability.…”

“…These aspects have different meanings depending on the analyzed situation [16]. In the stability studies of mining works, these aspects are of primary importance in the sense that if a cause causes the disturbance of the equilibrium of the rock massif, then it tends towards a new state of equilibrium, visibly characterized by deformations [11,12]. The mechanical characteristics of rocks can be determined by laboratory and/or in situ tests.…”

“…The mechanical characteristics of rocks can be determined by laboratory and/or in situ tests. The establishment and knowledge of these properties are conditioned by the fact that the mechanical parameters of the salt depend to a certain extent on its physical state, and with the passage of time, these parameters can change under the influence of different factors [9,12,15,[17][18][19]. At deposits of useful mineral substances of low commercial value (rock salt, potassium and magnesium salts, some iron ores, gypsum, chalk, etc.…”

“…At the current stage, the theoretical treatment of the pressure regime includes a large number of problems; however, difficulties arise when solving the problems encountered in mining engineering practice through classical analytical methods. That is why many concerns are directed in particular towards finding research methods, respectively, appropriate calculations for the problems and precision required by the mining activity [11,12,17,18,20,24,29]; others refer to finding experimental procedures for determining the behavior of underground constructions of all kinds using different modeling systems and in situ measurements [7,8,19,20,24,25,[28][29][30][31][32][33]. Finding that, in the end, the analytical way is not at all inferior to the experimental one, the analytical and numerical methods of solving the most diverse problems encountered in practice have also seen an exceptional development [34][35][36].…”

“…In the case of the reopening of some mining fields within the salt panels and the exploitation in depth with square pillars, the establishment of the optimal parameters of the elements of the exploitation system requires the establishment of 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 [27,[37][38][39]. The way of appearance, distribution, and manifestation of the secondary stress state, as well as its magnitude, is not only a characteristic of the salt massif because it is not dependent only on its quality but is a function of the "complete and inseparable interaction" of a complex of natural, technical, mining, and organizational factors [7,[11][12][13][14][15]22,23,31,36,39,40]. Studies related to the analytical assessment of the stability of the dry rock salt exploitation system with the increase in depth were carried out in the paper [12].…”