Energies

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19 pages, 7818 KiB

Open AccessArticle

Seismic Mitigation Effect of Overlying Weakening Strata in Underground Coal Mines

by Jiaxin Zhuang, Zonglong Mu, Xiufeng Zhang, Wu Cai, Anye Cao, Chunlong Jiang and Piotr Małkowski

Energies 2023, 16(16), 5958; https://doi.org/10.3390/en16165958 - 12 Aug 2023

Cited by 1 | Viewed by 1181

Abstract

Artificial construction of a weakening zone over the roadway is an essential method for preventing coal bursts and rock bursts caused by strong mining tremors. However, concerning the seismic absorption and load reduction capabilities of an artificial structural weakening zone, the degree of [...] Read more.

Artificial construction of a weakening zone over the roadway is an essential method for preventing coal bursts and rock bursts caused by strong mining tremors. However, concerning the seismic absorption and load reduction capabilities of an artificial structural weakening zone, the degree of rock mass damage to the roadway under weakening zone protection remains unclear. This study employed principles of elasticity and UDEC (Universal Distinct Element Code) to explore the seismic attenuation and load reduction capabilities of the weakening zone. The results indicate that the absorbing ability of the weakening zone increases exponentially with its weakening coefficient. Under the same dynamic load disturbance, when the weakening coefficient rises from 0.00 to 0.99, the sidewall displacement from the elastic wave source side changes from 0.400 m to 0.228 m. The total number of cracks in the roadway-surrounding rock, and the ranges of overstressed zones decreased linearly. The critical threshold of the roadway resisting the mining tremor disturbance increased. In particular, when the mining tremor is located directly above the roadway, the initial deformation of the roof is the largest, and the cumulative deformation of the rib is greater than the roof. By creating a weakening zone with a coefficient exceeding 0.95, the roadway remains unaffected by the 20 MPa dynamic loading. The study provides a theoretical basis for controlling coal burst that is triggered by mining tremors. Full article

(This article belongs to the Special Issue Coal Mining)

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15 pages, 3766 KiB

Open AccessArticle

Ground Motion Prediction of High-Energy Mining Seismic Events: A Bootstrap Approach

by Piotr Bańka, Adam Lurka and Łukasz Szuła

Energies 2023, 16(10), 4075; https://doi.org/10.3390/en16104075 - 13 May 2023

Cited by 2 | Viewed by 1866

Abstract

Induced seismicity has been a serious problem for many coal mines in the Upper Silesian Coal Basin in Poland for many decades. The occurring mining tremors of the rock mass generate seismic vibrations that cause concern to the local population and in some [...] Read more.

Induced seismicity has been a serious problem for many coal mines in the Upper Silesian Coal Basin in Poland for many decades. The occurring mining tremors of the rock mass generate seismic vibrations that cause concern to the local population and in some rare cases lead to partial damage to buildings on the surface. The estimation of peak ground acceleration values caused by high energy mining seismic tremors is an important part of seismic hazard assessment in mining areas. A specially designed bootstrapping procedure has been applied to estimate the ground motion prediction model and makes it possible to calculate the confidence intervals of these peak ground acceleration values with no assumptions about the statistical distribution of the recorded seismic data. Monte Carlo sampling with the replacement for 132 seismic records measured for mining seismic tremors exceeding 150 mm/s² have been performed to estimate the mean peak ground acceleration values and the corresponding upper limits of 95% confidence intervals. The specially designed bootstrap procedure and obtained ground motion prediction model reflect much better the observed PGA values and therefore provide more accurate PGA estimators compared to the GMPE model from multiple regression analysis. The bootstrap analysis of recorded peak ground acceleration values of high-energy mining tremors provides significant information on the level of seismic hazard on the surface infrastructure. A new tool has been proposed that allows for more reliable determination of PGA estimators and identification in the areas in coal mines that are prone to high-energy seismic activity. Full article

(This article belongs to the Special Issue Coal Mining)

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18 pages, 6138 KiB

Open AccessArticle

Different Prevention Effects of Ventilation Dilution on Methane Accumulation at High Temperature Zone in Coal Mine Goafs

by Lin Li, Tiantian Liu, Zhiqiang Li, Xiangjun Chen, Lin Wang and Shuailong Feng

Energies 2023, 16(7), 3168; https://doi.org/10.3390/en16073168 - 31 Mar 2023

Cited by 5 | Viewed by 1886

Abstract

In coal mine goafs, spontaneous combustion of coal can result in methane accumulation, which raises the danger of methane explosion disasters. As an atmospheric control tool, ventilation is applied to ensure air quality for avoiding disasters in underground mines. However, during the process [...] Read more.

In coal mine goafs, spontaneous combustion of coal can result in methane accumulation, which raises the danger of methane explosion disasters. As an atmospheric control tool, ventilation is applied to ensure air quality for avoiding disasters in underground mines. However, during the process of the spontaneous combustion of coal in coal mine goafs, the impact of ventilation dilution on the possible methane explosions induced by coal combustion has not been well investigated. In this study, a validated gas flow model for the spontaneous coal combustion environment in goafs of coal mines is adopted to investigate the influence of ventilation dilution at the three stages of the spontaneous combustion of coal. The research conclusions suggest that (1) ventilation dilution is a quick measure to dilute methane concentration and intensify heat transfer in the vertical direction in coal mine goafs; (2) ventilation dilution can lessen the danger of methane explosions by diluting methane concentration to the lower explosive limit for methane when coal combustion takes place on the air-inlet side; (3) however, ventilation dilution increases the methane explosion risk by decreasing methane concentration, resulting in explosive methane limits, if coal combustion occurs on the air-return side. This provides a reference for the management of ventilation during a spontaneous coal combustion disaster in the goafs of coal mines with methane. Full article

(This article belongs to the Special Issue Coal Mining)

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16 pages, 6635 KiB

Open AccessArticle

Assessment and Duration of the Surface Subsidence after the End of Mining Operations

by Mateusz Dudek, Anton Sroka, Krzysztof Tajduś, Rafał Misa and Dawid Mrocheń

Energies 2022, 15(22), 8711; https://doi.org/10.3390/en15228711 - 19 Nov 2022

Cited by 7 | Viewed by 1870

Abstract

The change in the European Union’s policy related to the energy transformation of Europe and the departure from fossil energy resources may contribute to the accelerated closure of many coal mines. Therefore, it is necessary to solve the problem of surface subsidence after [...] Read more.

The change in the European Union’s policy related to the energy transformation of Europe and the departure from fossil energy resources may contribute to the accelerated closure of many coal mines. Therefore, it is necessary to solve the problem of surface subsidence after the end of underground mining and the related suitability of post-mining areas for the re-use of the so-called problem of the reclamation of post-mining areas. In the case of areas suitable for re-use, it is necessary to determine the value of the final subsidence. It is also important to specify the time after which mining influences will no longer have a significant impact on the surface infrastructure and the environment. Analyses of the observed subsidence after the end of the mining operation indicate that this process may last from several months to several dozens or even several hundreds of years. It depends on the individual characteristics of the mining area, including the depth of exploitation, mining system, the behavior of the surrounding rock mass, etc. The article presents an in-depth analysis of residual subsidence and its duration using the proprietary forecasting method and the Gauss–Markov algorithm based on the example of the German Lohberg mine (Ruhr District), whose mining activity was completed in January 2006. Full article

(This article belongs to the Special Issue Coal Mining)

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20 pages, 17854 KiB

Open AccessArticle

Slope Stability Numerical Analysis and Landslide Prevention of Coal Mine Waste Dump under the Impact of Rainfall—A Case Study of Janina Mine, Poland

by Phu Minh Vuong Nguyen, Aleksander Wrana, Sylwester Rajwa, Zenon Różański and Robert Frączek

Energies 2022, 15(21), 8311; https://doi.org/10.3390/en15218311 - 7 Nov 2022

Cited by 19 | Viewed by 3298

Abstract

In Poland, the mining waste from underground coal mines is commonly deposited in surface dump sites, forming slopes or piles of materials dozens of meters high. Because of the loose structure of a mine waste dump slope, landslides may occur after a heavy [...] Read more.

In Poland, the mining waste from underground coal mines is commonly deposited in surface dump sites, forming slopes or piles of materials dozens of meters high. Because of the loose structure of a mine waste dump slope, landslides may occur after a heavy rainfall. This requires significant labor costs in reforming the mine waste dump sites and disturbs the continuity of the depositing operations. Moreover, if the mine waste dump sites located in the built-up areas, such as in the Janina mine waste dump, landslides apparently can threaten even lives and properties. Therefore, a mine waste dump stability analysis is necessary for ensuring safety. In this paper, slope stability analysis was conducted using numerical modeling under the impact of rainfall for the Janina mine waste dump, located in Libiąż, Poland. The results indicated that slope tends to loose stability in case of high rainfall intensity and short duration. Then, slope reinforcement using soil nailing and steel mesh was proposed to prevent landslide under the impact of high rainfall intensity. Once again, slope stability analysis was carried out with selected reinforcement. Meanwhile, slope monitoring was performed to assess the slope reinforcement implementation at the Janina mine waste dumps against the impact of high rainfall intensity. Based on the modeling and monitoring outcomes, assessments of slope stability and selected landslide prevention measures for the Janina mine waste dump under the impact of rainfall were presented. Full article

(This article belongs to the Special Issue Coal Mining)

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16 pages, 1673 KiB

Open AccessArticle

Analysis of the Scope for Reducing the Level of Energy Consumption of Crew Transport in an Underground Mining Plant Using a Conveyor Belt System Mining Plant

by Paweł Bogacz, Łukasz Cieślik, Dawid Osowski and Paweł Kochaj

Energies 2022, 15(20), 7691; https://doi.org/10.3390/en15207691 - 18 Oct 2022

Cited by 5 | Viewed by 2158

Abstract

One of the main elements that shape the production process in an underground mining plant is, in the broadest sense of the word, transport. Currently, a large amount of rolling stock from cable cars or suspended railways is maintained in mining plants, along [...] Read more.

One of the main elements that shape the production process in an underground mining plant is, in the broadest sense of the word, transport. Currently, a large amount of rolling stock from cable cars or suspended railways is maintained in mining plants, along with extensive infrastructure used for transporting crew and materials. The development of conveyor belt transport systems, as well as system process management, is increasing efficiency levels. Mining transport is a complex process, requiring large amounts of energy, which incurs significant production costs. We conduct a comparative analysis of the human transport system using a suspended railway with belt transport at Lubelski Węgiel “Bogdanka” Spółka Akcyjna (the largest hard coal mine in Poland), in terms of energy efficiency levels. We found that the process of transporting the crew in an underground mining plant to the production site using a conveyor belt system was less energy-intensive, and therefore created less emissions than the currently used model based on suspended queues. The analyses for the above project were conducted according to a model that was based on the study and analysis phase of the project through to its implementation and transfer to operational activities. The analysis was carried out based on the created simulation model, taking into account all elements of the crew transport process to and from the mining area. The implementation of the technical solution allowed for nearly a threefold reduction in the level of energy consumption and emissivity. In the analyzed model, the energy consumption in the first phase of production was 3.04 kWh per employee using the diesel rails system and 1.13 per employee using the belt conveyor system. Full article

(This article belongs to the Special Issue Coal Mining)

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17 pages, 3390 KiB

Open AccessArticle

Comparative Analysis of the Failure Rates of Shearer and Plow Systems—A Case Study

by Łukasz Bołoz, Zbigniew Rak and Jerzy Stasica

Energies 2022, 15(17), 6170; https://doi.org/10.3390/en15176170 - 25 Aug 2022

Cited by 5 | Viewed by 1721

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Coal Mining)

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14 pages, 6480 KiB

Open AccessArticle

Measurement of Forces in a Mining Plough Chain during Operation

by Mariusz Szot, Łukasz Herezy, Piotr Szade and Witold Frąc

Energies 2022, 15(16), 6003; https://doi.org/10.3390/en15166003 - 18 Aug 2022

Cited by 1 | Viewed by 1850

Abstract

Pulling chains are one of the most critical components of a plough longwall system. Their failure is hard to predict and results in costly and lengthy downtimes. Measurements of the actual forces acting on a plough chain are needed as they can provide [...] Read more.

Pulling chains are one of the most critical components of a plough longwall system. Their failure is hard to predict and results in costly and lengthy downtimes. Measurements of the actual forces acting on a plough chain are needed as they can provide important information about the nature of their operation and contribute to preventing their wear and failure by supplementing data gathered by a plough control station. In this work, a strain gauge system for the measurement of the forces in a plough chain is designed, manufactured and tested under real conditions for the first time. Constructed using a cylindrical strain gauge and widely available electronic components, the finished sensor was calibrated on a testing machine and used to measure forces in a 42 × 137 plough chain at LW Bogdanka. Measurements conducted under real conditions show that forces in the chain during steady ploughing does not exceed 400 kN. However, the forces peaked to up to 728.6 kN at certain points in the operation. The implications of such events are discussed. The device allowed for successful measurements of forces in difficult conditions of a mining plough longwall and provides new information on their course and characteristics, which is very valuable for plough operators and chain-life predictions. This work suggests the further integration of force sensors into longwall plough system. Full article

(This article belongs to the Special Issue Coal Mining)

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16 pages, 12100 KiB

Open AccessArticle

Study of the Abnormal CO-Exceedance Phenomenon in the Tailgate Corner of a Low Metamorphic Coal Seam

by Lei Li, Ting Ren, Xiaoxing Zhong and Jiantao Wang

Energies 2022, 15(15), 5380; https://doi.org/10.3390/en15155380 - 25 Jul 2022

Cited by 6 | Viewed by 1583

Abstract

Given the difficulty of early warning of coal spontaneous combustion caused by continuous abnormal exceedance of CO in the tailgate corner of a low metamorphic coal seam and taking the 1305-working face of the Dananhu No.1 coal mine in Hami, Xinjiang as an [...] Read more.

Given the difficulty of early warning of coal spontaneous combustion caused by continuous abnormal exceedance of CO in the tailgate corner of a low metamorphic coal seam and taking the 1305-working face of the Dananhu No.1 coal mine in Hami, Xinjiang as an example, this paper studies the abnormal CO-exceedance phenomenon based on field measurements, experimental research, and numerical simulation. The research shows that the abnormal CO-exceedance phenomenon is not caused by spontaneous combustion oxidation but by ambient-temperature oxidation of coal in the goaf. Factors, such as higher amounts of residual coal and higher degrees of fragmentation of the goaf, provide opportunities for the ambient-temperature oxidation of residual coal in the 1305 goaf. The 1305 coal oxidation characteristics at ambient temperature are examined, and the abnormal CO-exceedance mechanism is analyzed in depth. A CO-early-warning-limit model in the tailgate corner for coal spontaneous combustion in the 1305 goaf is established, and the scientific problems needing to be solved by further research are also discussed. The relevant research results have an important guiding significance for improving scholars’ understandings of CO exceedance in similar low metamorphic coal seams and the early warning of coal spontaneous combustion. Full article

(This article belongs to the Special Issue Coal Mining)

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20 pages, 6619 KiB

Open AccessFeature PaperArticle

Prediction of the Absolute Methane Emission Rate for Longwall Caving Extraction Based on Rock Mass Modelling—A Case Study

by Phu Minh Vuong Nguyen, Andrzej Walentek, Krystian Wierzbiński and Marian Zmarzły

Energies 2022, 15(14), 4958; https://doi.org/10.3390/en15144958 - 6 Jul 2022

Cited by 4 | Viewed by 1579

Abstract

This article presents a methodology for predicting the absolute methane emission rate for longwall caving extraction based on the determination of destressing zones generated by longwall mining operations, by means of numerical modelling. This methodology was applied for the conditions of the K-2 [...] Read more.

This article presents a methodology for predicting the absolute methane emission rate for longwall caving extraction based on the determination of destressing zones generated by longwall mining operations, by means of numerical modelling. This methodology was applied for the conditions of the K-2 longwall panel in the KWK Pniówek mine. The finite difference method code FLAC2D was employed as an element of the methodology to determine the destressing zones. All results including the numerical modelling results, empirical results and the measured (in situ) results were gathered in the comparative analysis. As the final results, the accuracy and reliability of the proposed methodology were evaluated. Full article

(This article belongs to the Special Issue Coal Mining)

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27 pages, 12482 KiB

Open AccessArticle

Modeling of Floor Heave in Underground Roadways in Dry and Waterlogged Conditions

by Piotr Małkowski, Łukasz Ostrowski and Jerzy Stasica

Energies 2022, 15(12), 4340; https://doi.org/10.3390/en15124340 - 14 Jun 2022

Cited by 24 | Viewed by 2356

Abstract

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 [...] Read more.

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%. Full article

(This article belongs to the Special Issue Coal Mining)

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Review

Jump to: Research, Other

26 pages, 8849 KiB

Open AccessReview

An Overview of Possibilities of Increasing the Permissible Speed of Underground Suspended Monorails for Transporting People in the Conditions of Polish Underground Mining

by Jerzy Świder, Kamil Szewerda, Jarosław Tokarczyk, Franciszek Plewa, Aneta Grodzicka and Krzysztof Kędzia

Energies 2023, 16(9), 3703; https://doi.org/10.3390/en16093703 - 26 Apr 2023

Cited by 4 | Viewed by 1847

Abstract

The permissible speed of suspended monorails in underground mines is determined by the internal regulations of each country and depends on the type of transportation. In the case of passenger transportation, the maximal driving speed in Polish underground mining regulations is 2 ms [...] Read more.

The permissible speed of suspended monorails in underground mines is determined by the internal regulations of each country and depends on the type of transportation. In the case of passenger transportation, the maximal driving speed in Polish underground mining regulations is 2 ms⁻¹. Regarding the higher permitted driving speed in other countries, it is reasonable to consider changes to these regulations that would raise the permitted speed limit. Increasing the permissible travel speed would improve the efficiency of mining operations because of the significant reduction in the inefficient working time of miners traveling on the monorail from the shaft to their place of work. However, at the same time, an increase in the permissible speed of travel results in higher values of forces and accelerations affecting both the crew riding the train and the underground working infrastructure (the suspended route, slings, and arches yielding support). The results of the series of works carried out at the KOMAG Institute of Mining Technology to assess the impact of increasing the speed on the safety of both the crew and the mine infrastructure are presented in this article. For this purpose, several numerical simulations were conducted, considering the emergency braking of the suspended monorail during which the overloads are the greatest. The result of the simulations was the analysis of the effects of driving and emergency braking of the suspended monorail with increased travel speed on the following: the overloads acting on the crew being transported and the forces acting on the suspended monorail route, including the forces in each sling. Next, a potential solution for improving safety was developed. The development of the algorithm for an innovative method of sequential emergency braking of the monorail in the case of passenger transportation was one of the important solutions. Full article

(This article belongs to the Special Issue Coal Mining)

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Other

Jump to: Research, Review

16 pages, 3309 KiB

Open AccessPerspective

Research into Impact of Leaving Waste Rocks in the Mined-Out Space on the Geomechanical State of the Rock Mass Surrounding the Longwall Face

by Adam Smoliński, Dmyto Malashkevych, Mykhailo Petlovanyi, Kanay Rysbekov, Vasyl Lozynskyi and Kateryna Sai

Energies 2022, 15(24), 9522; https://doi.org/10.3390/en15249522 - 15 Dec 2022

Cited by 59 | Viewed by 2693

Abstract

Backfilling technology is not always used by mining enterprises, which is conditioned by technological and economic factors, such as the need for high mining rates and costs for the technological processes of transporting backfill materials from the daylight surface to the mined-out space. [...] Read more.

Backfilling technology is not always used by mining enterprises, which is conditioned by technological and economic factors, such as the need for high mining rates and costs for the technological processes of transporting backfill materials from the daylight surface to the mined-out space. This concerns the underground mining of hard coal, which is a strategic energy resource, in the mines of Ukraine. This paper aims to study the effect of leaving the waste bottom rocks in the mined-out space of the longwall face without their drawing to the earth’s surface on the geomechanical state of the rocks surrounding the longwall face. The geomechanical assessment of the stress state of the rock mass surrounding the longwall face, when leaving the waste rocks from the seam bottom rocks in the mined-out space, is performed by the finite element method using the Ansys software package. A geomechanical model has been developed and substantiated, which adequately reflects the mining-geological conditions for seam mining within the extraction site, the actual structure and properties of the coal-bearing rock stratum, the parameters of the longwall face and the modified powered support for the processes of leaving the rocks in the mined-out space. The values and patterns have been determined of the decrease in the stress intensity concentrations in the coal-bearing roof mass in the frontal bearing pressure zone and destressing zone with an increase in the ratio of the rock pack thickness to the extracting seam thickness. The relative indicators of the load on the powered support section and the lowering of its roof have been determined by the ratio of the thickness of the rock pack formed in the mined-out space to the extracting seam thickness. The proposed mining method is of significant commercial and research interest for owners of coal mines developing thin coal seams because environmental costs for placing waste on the surface are reduced, and the energy potential of coal is increased due to the separation of waste rocks from coal in underground conditions. The need for a cycle of beneficiation of mined mass is eliminated and the geomechanical conditions of coal mining processes are improved. Full article

(This article belongs to the Special Issue Coal Mining)

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