# Stability Analysis of the Exploitation System with Room and Pillar by Analytical Methods
###### Abstract  
The mining method that is still often used in salt deposits is the room-and-pillar mining method, in which the dimensioning of the most requested element in the system is followed. The pillars are the elements subjected to the greatest loads. Knowing the size and distribution mode of the secondary state of stress--deformation--is a necessity that can lead to the design and realization of stable, reliable underground excavations. This paper proposes an analytical assessment model of the secondary stress state in the pillars between the operating rooms, as well as in the whole system room-pillar-floor, based on the results obtained from laboratory research through modeling and in situ research. For this purpose, the evaluation of the secondary stress state was carried out considering the following methods: (1) the dimensioning method based on the theory of limit equilibrium, taking into account the effective stress in the pillars; and (2) the mechanics of the continuous environment based on the design of some analytical models for evaluating the secondary stress-deformation state in the pillar and floor. The exploitation of one of the largest salt deposits in Romania is used as a case study, and the stability of the exploitation system with rooms and pillars is evaluated by analytical methods. The secondary state of tension was calculated at different points on the height of the pillar. Through the proposed algorithm, the value of the axial component of the secondary stress state at different points along the axis of a pillar located at a depth of 100 m varies between 1.498 and 1.657 MPa, compared to the value obtained by the finite element method and in situ measurements, which was 1.64 MPa. The comparison revealed a high degree of agreement between the results obtained for the depth of 100 m using both the FEM and laboratory and in situ measurements. This suggests that the proposed algorithm is a reliable method for predicting the secondary stress state. The presented algorithm can be extended in the field of mining deposits, where mining methods with rooms and pillars are used. s 2024 14 1827 2024 2024 2024 2024 2024 2024 2024 2  
to analyze the stability of the underground works performed in such massifs, it is necessary to know in the first stage the main properties that need to be taken into account and studied: geological, physical, mechanical, and deformation characteristics [1; 4; 6]. The basic parameters considered must offer the possibility of obtaining the necessary data and information to be able to elucidate the geomechanical processes that manifest themselves in the salt massif and establish analytical methods and models for the interpretation of these processes [8]. Based on them, an efficient design can be carried out on the geometric and technological parameters of the salt exploitation methods, especially in conditions where the exploitation depth increases [9; 10; 11]. 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.