Floor heaving is a phenomenon that occurs in almost all mining roadways and tunnels. It can restrain the advance of the heading face or cause serious problems during roadway use. The highest levels of floor uplifting are observed in coal mines, which can reduce the output or even stop it altogether. The floor heaving intensity depends on the rock type, the stress in the rock mass, and rocks’ mechanical properties. Floor deformation develops when the secondary state of stress is formed around the working, and it is much higher and more dynamic in the case of waterlogged rocks. The presence of water increases the floor’s propensity to heave, especially clay rocks, such as claystones or mudstones, if they include water-absorbed minerals. In this paper, we present a new modeling methodology for roadway floor heave. The modeling covers a dry floor condition in which the parameters of the Hoek-Brown failure criterion are gradually lowered over time, and a waterlogged floor condition, in which the strength and strain parameters of the rocks are gradually reduced in line with their progressive saturation. In the second case, the claystone floor’s geomechanical parameters were investigated, and the rocks were subjected to water for up to 24 h. The results of the numerical simulation were compared with the in situ measurements of convergence and floor heave in the same coal mines from which the rock samples were collected. The consistency between the numerical simulations and the underground measurements reached 90–99%.
This paper presents basic mineralogical and petrological data of the rocks hosting larimar deposit from the Sierra de Bahoruco, in the SW part of the Dominican Republic. Larimar is a unique ornamental stone with a wealth of decorative qualities. The Las Filipinas Larimar Mine in Barahona Province is the only place of this type in the world. Its production and distribution require radical action; hence, the paper also provides current information on the extraction of this raw material and prospects for the future. The paper indicates the possibility of using a new adit support system based on a mixed support (arch support and shotcrete). Numerical analysis shows the need to create a shotcrete coating around the entire circumference, about 15 cm thick. The variable geotechnical situation around the excavation, caused by the planned operation, prompts the use of slightly different solutions in the field of support. The article presents an outline of the technology using Polish experience. It is a support-bolt casing system with the latest achievements in this field.
This paper presents our experience obtained when mining the thick and steeply-inclined Seam 510 in the Polish Kazimierz-Juliusz coal mine with the use of a unique mechanical face mining system. Seam 510, which is 15–20 m thick and inclined at angles of 40°–45°, was initially treated as uneconomical because effective mining systems were not available. However, to extract high-quality coal resources, a completely mechanized variant of the sublevel caving system was designed based on standard machines and equipment applied in coal mining. Extraction was conducted top-down at the levels of the particular mining sub-level drifts with roof caving. The faces in the extracted coal release areas were protected by a single pair of specially designed mechanized mining system sections. One of the basic problems revealed during extraction of subsequent mining panels, was the observed changeability of the resource mining rates. The extraction losses changed in the available resources from less than 10% to about 50%. This paper presents two typical courses of changes in the extractable resource mining rates. Similar rate changes occurred in both cases with continued mining of a single seam section. Our analysis enabled deposit loss estimations and production output planning under the sublevel caving systems applied in the extraction of seam deposits of similar structure.
Mechanised plow and shearer systems are widely applied in underground mines all over the world. Both systems are used in the exploitation of hard coal deposited in the form of seams of various thickness. The selection of the appropriate complex depends on the mining and geological conditions and the thickness of the seam. However, with regard to thin and medium seams, these complexes are competitive solutions. Mines usually use either shearer or plow systems. Both have certain advantages and disadvantages resulting from their design and method of operation, which have been demonstrated and presented in many publications. However, in terms of their failure rate comparison, there are no relevant research and analysis results. Only selective studies of individual machines can be found. The article is concerned with the failure frequency of longwalls equipped with plow and shearer systems in the LW Bogdanka coal mine. The analysis covers a period of 13 months of the mine’s operation, during which 2589 failures were recorded. All failures were taken into account, irrespective of their type or cause. The analysis was conducted for all longwalls exploited in this period, i.e., five plow and five shearer systems working in six different sections. In the analysed period, these longwalls worked for a total of 1484 days. It should be emphasised that all the complexes worked in one mine, thanks to which the data are comparable. The analysis is unique material regarding the failure rate of machines. Both solutions were analysed independently and subjected to a detailed comparison. A comprehensive analysis revealed that the failure rate of longwalls equipped with plow systems is noticeably higher than that of shearer ones. The main purpose of the article was to conduct a comparative analysis of the failure rate of machines in shearer and plow complexes operating in the same conditions. The analysis results contradict the previous opinion on the failure frequency of plow and shearer systems. The final conclusion has been very well-argued and is supported by hard data. The comparison of both techniques in terms of their failure rate is new knowledge and can be treated as an argument when choosing an appropriate longwall complex.
Widespread in Polish hard coal mining, cable bolts are used to reinforce the arch yielding support of roadways. This article attempts to prove that change in approach to long bolting technology can bring significant benefits in terms of improving the stability of roadways, including limiting the development of the fracturing zone in the roof, and ultimately also increasing the frame spacing of arch yielding support. The article contains the results of numerical calculations using the finite element method showing the effect of pre-tensioning on the work of cable bolts installed in a situation when a zone of a fractured rock mass appeared in a roof excavation. As a result of the calculations, the dependence of the final vertical displacements of the roadways roof on different pre-tensioning variants of the cable bolts was presented. The second part of the article presents the practical aspects of the use of cable bolts with pre-tensioning in reinforcing the rock mass and arch yielding support of roadways. In addition, the article identifies the developments in bolting technology which could lead to an increase in work safety and reduce the costs of arch yielding support.
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