# Stability Analysis of the Exploitation System with Room and Pillar by Analytical Methods
## 2 Geomechanical, Technical, and Mining Considerations  
In this paper, we considered the exploitation of one of the largest salt deposits in Romania. The deposit is delimited by four types of tectonic accidents consisting of major faults, geological fractures, and local lines from the roof of the deposit [12; 43]. From a petrographic point of view, the salt that makes up the deposit has a macro or microcrystalline appearance, being impure with diagenetic dispersions consisting of clays, marls, sandstones, and crystalline limestones. Halite crystals appear in the form of cubes with frequent secondary fibrous developments [11; 12; 42; 44; 45]. The salt formation is considered a sedimentary rock of chemical precipitation; it has a banded texture, and its structure is homeoblastic or heteroblastic. It is a rock that can become plastic at low pressures and temperatures [12; 42]. Two permeable aquifer horizons were highlighted, at 15-17 m and 45-47 m, made of fine sands. At depths of 1028-1128 m, three horizons of salinized thermal waters were identified. In the laboratory (Figure 1), the physical, strength, and deformation characteristics of salt from categories I-III were determined, as well as for heterogeneous salt [11; 12; 42]. The apparent specific weight has an average value of 2.0945 \(\times\) 10\({}^{4}\) N/m\({}^{3}\) for the first category of salt (compact saccharide white salt) and 2.039 \(\times\) 10\({}^{4}\) N/m\({}^{3}\) for heterogeneous salt (third category). The average value of the uniaxial compressive strength varies from 24.5 MPa for the first category of salt to 17.95 MPa for heterogeneous salt. The triaxial compressive strength of salt, whether axially symmetric or cylindrical, takes average values between the limits of 24.5 and 17.95 MPa (for categories I to III), and for heterogeneous salt, it has values of 14.2 and 26 MPa. Regarding the deformation behavior, depending on the quality of the salt, from the processing of the experimental data, it was found that the modulus of elasticity of the salt varies from 733 MPa for the salt of the third category to 1850 MPa for the first category of salt. Similarly, the same experimental data highlighted a variation in Poisson's ratio from values of 0.26 for the third category of salt to values of 0.42 for the first category. The deformations recorded after carrying out the static load tests confirm the fact that the salt has an elastic-viscous-plastic behavior [11; 42; 45; 46]. The appearance and orientation of the cracks revealed the fact that the salt is subjected to an inhomogeneous stress state, characterized in particular by the manifestation of tensile stresses in a quasi-orthogonal direction to the compression axis. The appearance and manifestation of these stresses are partially due to the variation, size, shape, and orientation of the constituent grains of the polycrystalline salt medium [11; 42]. Based on the values of the uniaxial compressive strength, this type of salt can be included in the class of rocks of low strength, according to the existing classifications in the literature [11; 12; 26; 42; 43; 44; 45; 46; 47] presenting values of the cohesion and the angle of internal friction determined both by shearing (c = 2.65 MPa and \(\varphi\) = 11\({}^{0}\)) and in triaxial (c triaxial = 7.9 MPa and \(\varphi_{\text{triaxial}}\) = 10\({}^{0}\)) specific to such rocks. Depending on the increase in lateral stresses \(\sigma_{\text{x}}=\sigma_{\text{y}}\) in the range (2.5-7.5) MPa, the triaxial compressive strength of the salt, axially symmetric or cylindrical, has average values between 22.1 and 29.58 MPa, a fact that reveals a reduced and nonlinear increase in this resistance with the application of lateral stresses. This salt deposit is in the form of a diapir, having superior physical and mechanical characteristics compared to the other salt deposits in the country, and therefore its exploitation can be carried out by dry means.