# Stability Analysis of the Exploitation System with Room and Pillar by Analytical Methods
###### Abstract
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. ), as well as at some rock deposits (limestone, marl, slate, kaolin, clays, etc. ), the rooms and pillars mining method (pillars that can be permanently or temporarily left) was and continues to be frequently applied. At the same time, this method is also applied when we do not want to cause displacements or shocks of the rocks from the roof of the exploited deposit, which would affect the land on the surface [20; 21; 22]. This method allows for efficient extraction of salt while minimizing the risk of structural damage to the surrounding rock formations [8; 15; 23; 24; 25]. The pillars provide natural support to prevent the collapse of the mine and maintain stability. The pillars have the role of taking over the static loads due to the weight of the corresponding part of the deposit itself and the rock formation in the roof [14; 19]. The pillars prevent caving and causing displacements that would produce subsidence and terrain subsidence. To be able to fulfill this role, the pillars must be correctly sized. The lithostatic pressure determines within the pillars compression and, less often, shear stress states, depending on their shape and size and the geological and petrographic characteristics of the salt [11; 23; 26]. [PERSON] et al. [15] analyze the characteristics of pillar instability and pillar loading. To evaluate the stability of the pillars, the safety factor is used, and the results obtained lead to the conclusion that the depth and uniaxial compressive strength are the most important, followed by the height and width of the pillars, the width of the rooms, and the weight of the overlying rocks. Based on the in situ experimental tests, [PERSON] et al. [23] performed a regression analysis to develop statistical models for the in situ stress and the in situ elastic modulus. The authors of the paper [23] developed a quick orientation chart to determine the appropriate pillar length for a given span and the required safety level. [PERSON] et al. [8] study the problem of the stability of underground structures in the case of their use for the purpose of gas storage in large salt caverns. The current research points out that the major problem is that the design of safety pillars has not been systematic due to the differences in salt rock in the region, and the engineering of salt pillar design still relies on experience. The time deformations of salt play an important role in the design calculations, dimensioning, and ensuring the stability of underground works (cavities filled with brine or rooms and pillars), which depend a lot on the solubility of the salt in water and its permeability to gas and brine [3; 5; 6; 14; 27]. The rheology of rock salt deposits is much more complex compared to others because they are the place where phenomena of different natures take place, for example, phenomena related to the polycrystalline structure of the salt (dislocation movements, polygonization, interactions between crystals, etc.) or phenomena related to the high solubility of NaCl in water (phenomena such as brine migration, fluid-assisted matter transport, scarring, etc. ); phenomena related to cracking and fracturing are common to all rocks [14; 28; 29]. These are coupled with other phenomena that influence the mechanical, thermal, hydraulic, and chemical behavior of the salt [28; 29; 30]. 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.