Thick coal seam no. 3, block V, Lupeni mine was mined by longwall top coal caving (LTCC). After the coal mining, the ground surface underwent continuous subsidence, but since 2008, three sinkholes have appeared on the surface with important dimensions, atypical for the geo-mining conditions in this coal basin. This article is a synthesis of the study meant to decipher the geo-mechanical phenomenon that led to the emergence of these sinkholes and highlighting the main factors that contributed to the development of this phenomenon. For this purpose, measurements were made on the terrain deformations using photogrammetric methods and aerial laser scanning, when modeling with 3D finite elements, in elasto-plasticity and with the help of the Knothe–Budrik influence function. The factors that contributed to the occurrence of discontinuous subsidence phenomena are shallow mining depth, the LTCC mining method, and the presence of faults in the vicinity of the mining panels. Additionally, the geo-mechanical phenomena of subsidence terrace development and sinkholes in the mining subsidence troughs at the Lupeni mine were described.

The hard coal seams in the Jiu Valley mining basin have been mined with different mining methods and technologies, including with the complete caving of the surrounding rocks and with top coal caving. These mining systems have led to the degradation of the ground surface by producing subsidence of the land, ranging from a few meters up to tens of meters, in the areas with thick coal seams with high dips. When the limits of the main safety pillars are accidentally exceeded whilst mining, buildings situated either below the ground or on the surface are affected. In the future, the possibility exists of mining some of the very large reserves that are immobilized in the main safety pillars, where the gentle dip seams are stored. In consideration of the above, in order to study the behaviour of typical buildings that are under the influence of underground mining and to develop a model of the stress state in the structural elements of the structures, finite element modelling is used. As such, several modelled buildings with one, two, and three levels were generated, as well as buildings with two levels and with different lengths. These buildings were built of reinforced concrete panels or brick masonry and were subjected to the mining influence of a panel specific to the mines in the Jiu Valley basin, sequentially extracted with a longwall coal face method at different operating heights, with the use of roof control by caving of rocks and with top coal caving methods. Following the analysis of the major principal (tensile) stresses and minor principal (compressive) stresses, a series of conclusions regarding the behaviour of these buildings that are under the influence of the underground mining is revealed. In this context, it was concluded that the value and location of the stresses developed in the structure of the buildings depend mainly on the extension of the panel and the volume of the goaf, the relative position of the building in respect to the coal face line, and the length of the building.

To increase the economic and technical performances of the Jiu Valley hard coal mines, the top coal caving, in horizontal slices, mining methods (Bourbaki methods) were introduced, adapted to the local geo-mining conditions. This mining was successfully experimented by using classical technology, using the individual supports and coal blasting. In the future, it is planned to adopt the mechanized technology, with frame supports and shearers. The mechanized longwall faces with top coal caving mining, in horizontal slices, of coal seam no. 3 could be efficient only if the sizes of the top coal height and the panel length determine a minimum cost of production. Therefore, the goal of this paper is the optimization of these parameters, from a technical and economic point of view, taking into account the general model of the cost function, at the panel level. For that, it was necessary to make a certain sequence of analysis involving: technological unit establishment, purpose function and optimizing model. Thus, there attaining to the mathematical model of the unit cost, after determination of all the individual calculation articles, regarding the preparatory workings, coal face equipments, materials, energy, workforce, etc. Because of the complexity of the obtained technical and economic model, to determine the optimum sizes of the panel length and top coal height, it was necessary to archive a sensitivity analysis of the unit cost function to the main parameters implied into this mathematical model.

The underground mining of the rock salt deposit from Slănic started in 1665, with the Old Mines and continued in 1970, with Victoria Mine, then in 1993, with Cantacuzino Mine. The mining method applied at Victoria and Cantacuzino mines was the one with small rooms and square pillars, with which over 9.7 million m3 of rock salt were extracted. This very large volume of underground mining voids led to the convergence of the underground excavations and thus to the deformation of the surface. This article presents the analysis of the measurements of surface displacement and the prediction of its subsidence over time. Also, the main factors that contributed to the deformation of the surface are analyzed, namely: the dimensions of the underground voids, the mining depth, the geomechanical characteristics, the tectonics and microtectonics of the deposit, the hydrogeology and the effect of blasting.

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Increasing the mining depth at Praid Saline and implicitly the state of stresses and strains determines an increase in the dimensions of resistance structures (pillars and ceilings). Furthermore, the seismic effect generated by the detonation of explosives contributes to the degradation of resistance structures. In order to reduce the destructive effect of drilling-blasting technology a proposal is made for the implementation of mechanized salt cutting technology which makes use of a roadheader. This article emphasizes the technical-economical implementation advantages of exploitation from the lower horizons of the New Sector, those of mechanized mining with a roadheader as opposed to the classical technology of drilling-blasting.