Hard Coal Mining Research Articles

Influence of the Depth of Shallow Workings on the Probability of Sinkhole Formation and Determination of the Contribution of Mines to the Resulting Risk

AbstractThis paper presents a broad spectrum of factors that have an impact on the environment once underground mines have been closed, with particular emphasis on hard coal mines. Based on the review of scientific literature and own experience, several types of environmental impacts of closed mines were specified. In the author’s opinion, sinkholes pose the most serious hazard to post-mining areas. A high degree of urbanisation of the Upper Silesian Coal Basin and a wide range of mining operations conducted in the past necessitate the post-mining areas development for construction purposes. However, investing in these areas cannot carry risks and pose a threat to public safety. Therefore, a simplified method of determining the probability of sinkhole formation depending on the depth of a shallow void (excavation) in the rock mass was proposed. An algorithm has also been proposed for determining the contribution of individual mining companies to causing sinkhole hazard, which is of great importance in legal proceedings.

Groundwater in Katowice - center of a large urban and deep coal mining area in Poland

The paper presents the groundwater resources of Katowice and the results of studies conducted to identify prospective areas in aquifers with sufficient water resources for the location of public water intakes. The city of Katowice is the capital of Upper Silesia, the largest urban-industrial area in Poland, the region with a highly developed hard coal mining and many other different industries covering almost the entire scope of the economy. Due to long term drainage of mines causing the depletion and deterioration of groundwater and surface water resources, the main municipal water intakes have been located outside Katowice. Most of the pumped mine water is discharged into surface waters, causing significant salinity of water and disallow its use for municipal or industrial purposes in Katowice. The water collection and supply system is very extensive and covers a significant part of the Silesian agglomeration which is why Katowice is supplied with water from surface water intakes located outside the city. According to older published materials, such as the Hydrogeological map of Poland, there were no aquifers in the city that could have been used to supply the city with drinking water, however recent studies have shown that groundwater in the Quaternary aquifers in the western part of the city can be used to supply the city with public water. Less productive, Quaternary aquifers in north-eastern parts of the city may constitute the basis for drinking water supply in emergency situations, when surface intakes cannot be used, such as toxic, radiological or viral contamination or damage to the water supply network eg. as a result of an earthquake or warfare.

Analysis of spatio-temporal development of mining landforms using aerial photographs: Case study from the Ostrava–Karviná mining district

Abstract The anthropogenic relief transformations of the mining landscape are characterised by high dynamics of changes over time that can be effectively mapped on a large scale using aerial images. The Karviná part of the Ostrava-Karviná mining district, which stands for significant hard coal mining area in the Czech Republic, has been selected to analyse the spatio-temporal development of anthropogenic landforms. Anthropogenic landforms were visually identified from the aerial images from 1947, 1966, 1971, 1985, 1994, 2009, and 2018. Specific anthropogenic landforms were analysed along with their spatio-temporal changes based on obtained vector data. The total extent and number of anthropogenic landforms increased the most during the periods 1947–1966 and 1971–1985. The same anthropogenic landforms occurred on circa 24 hectares in the entire period 1947–2018. The most anthropogenic landforms remained preserved in the last observed period 2009–2018. The multi-temporal analysis of aerial photographs and overlay operations in GIS enabled to map the age of specific landforms and to identify changed or unchanged anthropogenic landforms. This method is suitable for the study of landform dynamics at mining sites and is particularly relevant for the planning challenges in post-mining reclamation.

Combining deep neural network and spatio-temporal clustering to automatically assess rockburst and seismic hazard – Case study from Marcel coal mine in Upper Silesian Basin, Poland

Mine induced seismic events are a major safety concern in mining and require careful monitoring and management to reduce their effects. Therefore, an essential step in assessing seismic and rock burst hazards is the analysis of mine seismicity. Recently, deep neural networks have been used to automatically determine seismic wave arrival times, surpassing human performance and allowing their use in seismic data analysis such as seismic event location and seismic energy calculation. In order to properly automate the rockburst and seismic hazard assessment deep neural network phase picker and a spatio-temporal clustering method were utilized. Seismic and rockburst hazards were statistically quantified using two-way contingency tables for two categorical variables: seismic energy level of mine tremors and number of clusters. Correlations between several spatio-temporal clusters and a statistical association between two categorical variables: seismic energy level and cluster number indicate an increase of seismic hazard in the Marcel hard coal mine in Poland. A new automated tool has been elaborated to automatically identify high-stress areas in mines in the form of spatio-temporal clusters.

Evaluation of mining landscape changes with development landscape metrics in the Ostrava-Karviná Mining District (Czech Republic).

The study presents an analysis of changes in the landscape of the Ostrava-Karviná Mining District (in the Czech Republic) covering the period of more than 170years. In the area of interest affected by underground coal mining, both areas affected by changes and land cover preserving areas were identified in the study. A detailed assessment of the landscape changes was enabled by using landscape metrics and indices, namely the development index and total landscape change index. The underlying data were obtained from maps of stable cadastre (from the year 1836) and aerial images of the years 1947, 1971, and 2009. Visual photointerpretation of aerial images and interpretation of the maps of stable cadastre made it possible to create land cover maps according to CORINE Land Cover categories. Obtained information on the representation of individual land cover categories were used to identify and to analyze changes in the landscape affected by hard coal mining.

Spatial modeling for detection of water retention capacity in technosols developed on carboniferous spoil heap after hard coal mining

Post-industrial areas, such as heaps, are an Anthropocene pressure on the environment but show natural potential for new ecosystem services, i.e., water retention, biodiversity, and C-sequestration. All these ecosystem functions of such sites can be developed only in the case of appropriate reclamation treatments, which are especially difficult under the conditions of carboniferous spoil heaps after coal deep mining. The study of reclamation effects has been increasingly supported in recent years by modern remote sensing techniques. This paper presents the possibilities of using selected remote sensing data and topographic indices and their effect on volumetric water content, which is crucial for habitat development. PlanetScope satellite imagery and airborne laser scanning point clouds were used to estimate the volumetric water content (VWC) of soil. This integrated analysis allows for more accurate spatial modeling of soil moisture, a key indicator of ecological restoration in degraded land. The method of generalized additive models was used to develop a predictive model. The developed predictive model was characterized by the following values of model accuracy evaluation parameters: MAE – 4.1%; RMSE – 5.6%; and R2–0.49. As a result of the analysis, topographic and spectral variables with significant influence on VWC were identified, and a map of the retention capacity of the Sosnica heap was developed.

Environmental relevance monitoring and assessment of ochreous precipitates, hydrochemistry and water sources from abandoned coal mine drainage

This study investigated the mineralogical and chemical characteristics of ochreous precipitates and mine water samples from abandoned Upper Carboniferous hard coal mines in an extensive former mining area in western Germany. Mine water characteristics have been monitored and assessed using a multi-methodological approach. Thirteen mine water discharge locations were sampled for hydrochemical analysis, with a total of 46 water samples seasonally collected in the whole study area for stable isotopic analyses. Mineralogical composition of 13 ochreous precipitates was identified by a combination of powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM/EDS). Results showed that abandoned mine drainage was characterized by circumneutral pH, Eh values ranging from 163 to 269 mV, relatively low concentrations of Fe and Mn, and was dominated by HCO3− > SO42− > Cl− > NO3− and Na+ > Ca2+ > Mg2+ > K+. Goethite and ferrihydrite were the dominant precipitated Fe minerals, with traces of quartz, dolomite, and clay minerals. Some metal and metalloid elements (Mn, Al, Si, and Ti) were found in the ochreous sediments. The role of bacteria in the formation of secondary minerals was assessed with the detection of Leptothrix ochracea. The δ18O and δ2H values of mine water plotted on and close to the GMWL and LMWLs indicated local derivation from meteoric water and represented the annual mean precipitation isotopic composition. Results might help to develop strategies for the management of water resources, contaminated mine water, and public health.

Coupled CFD-FEM analysis of the damage causes of the retention bunker: a case study at hard coal mine

Underground coal storage bunkers serve as crucial infrastructural components in the coal mining industry, providing secure and accessible locations for the storage of mined coal. The interaction between stored coal and underground water in coal storage bunkers indeed poses significant challenges due to the unpredictable nature of the resulting coal-water mixture. This phenomenon is particularly prevalent in coal mines operating under water hazards, where groundwater infiltration into storage areas can lead to the formation of coal-water mixtures, altering the physical properties of the stored coal. The interaction between coal and water can result in the formation of coal-water mixtures (hydromixture), which exhibit complex rheological properties. These mixtures may vary in viscosity, density, and particle size distribution, making their behavior difficult to predict. Underground water may exert hydrostatic pressure on the stored coal, influencing its mechanical behavior and compaction properties. Changes in pressure can result in coal compaction or expansion, affecting bunker stability and the integrity of surrounding rock strata. The main goal of the paper was to determine the values of pressure field variations exerted by the flowing hydromixture within underground coal storage bunkers. This objective reflects a critical aspect of understanding the dynamic behavior of coal-water mixtures (hydromixture) under varying conditions, particularly in environments where water hazards pose significant challenges to storage and operational stability. The paper utilized computational fluid dynamics (CFD) methods to examine the changes in pressure within underground coal storage bunkers induced by the flow of coal-water mixtures. The examination of damage to an underground coal storage bunker due to stress distribution was conducted using the finite element method (FEM). This computational technique is widely utilized in engineering and structural analysis to model complex systems and predict the behavior of materials under various loading conditions The results of the CFD numerical simulation were compared with the mathematical models.

Machine Learning-Based Classification of Rock Bursts in an Active Coal Mine Dominated by Non-Destructive Tremors

Rock bursts are dynamic phenomena in underground openings, causing damage to support and infrastructure, and are one of the main natural hazards in underground coal mines. The prediction of rock bursts is important for improving safety in mine openings. The hazard of rock bursts is correlated with seismic activity, but rock bursts are rare compared to non-destructive tremors. The five machine learning classifiers (multilayer perceptron, adaptive boosting, gradient boosting, K-nearest neighbors, and Gaussian naïve Bayes), along with an ensemble hard-voting classifier composed of these classifiers, were used to recognize rock bursts among the dominant non-destructive tremors. Machine learning models were trained and tested on ten sets of randomly selected data obtained from one of the active hard coal mines in the Upper Silesian Coal Basin, Poland. For each of the 627 cases in the database, 15 features representing geological, geomechanical, mining, and technical conditions in the opening as well as tremor energy and correlated peak particle velocity were determined. Geological and geomechanical parameters of the coal seams and surrounding rocks were aggregated into a single GEO index. The share of rock bursts in the database was only about 8.5%; therefore, the ADASYN balancing method, which addresses imbalanced datasets, was used. The ensemble hard-voting classifier most effectively classified rock bursts, with an average recall of 0.74.

Modified method for assessing the required expenditures and estimated time of hard coal mine liquidation

Modified method for assessing the required expenditures and estimated time of hard coal mine liquidation

Model of the Formation of Work Safety Culture in Polish Mining Enterprises

The article presents the results of research on the level of work safety culture, which is an important element influencing the organisational culture in mining enterprises. The article aims to measure the safety culture among managers in Polish hard coal mines. The assumed goal was achieved in the area of literature and empirical research. Research shows that the precise identification of hazards defined the thematic areas shaping safe working conditions in underground mines. The main part of the work was to survey 135 employees in 3 hard coal companies in Poland. The questionnaires were developed in cooperation with mining experts, and the 5-point Likert scale was used to evaluate individual questions. This methodological approach identified the subjective feelings and experiences of employees for building appropriate attitudes and behaviours that shape the organisational culture. The use of a culture grid enabled the creation of seven thematic groups of safety areas related to the so-called referents of organisational culture. The result of the empirical research is to propose an approach for the transformation of safety culture in the selected area for mining companies. The approach uses the organisational culture grid to shape the attitudes and behaviours of employees, which identifies and designates weak areas, defining them as unsatisfactory and unacceptable, and being the key conclusion of the research.

Biodiversity Characteristics and Carbon Sequestration Potential of Successional Woody Plants Versus Tree Plantation under Different Reclamation Treatments on Hard-Coal Mine Heaps––A Case Study from Upper Silesia

In the discussion about sustainable forestry, a key role is played by the development of ecosystem services, including ecological, social, and economic ones, in which biodiversity and carbon (C) sequestration are among the most important. Afforestation of disturbed and post-mining sites is one of the ways to minimize the negative impact of civilization on the environment. Optimizing C sequestration strategies at post-mining sites plays a crucial role in promoting ecosystem recovery, supporting climate change mitigation, and enabling C offsetting. In this study, we compared the C storage in the soil and plant biomass of forest ecosystems developed on coal-mine heaps for different scenarios of reclamation and succession. We tested combinations of sites (i.e., non-reclaimed sites on bare carboniferous rock [BR] and sites reclaimed by applying topsoil [TS]) and successional woodland and tree plantation. The estimated potential for total C storage (in the soil + biomass) for TS sites ranged from 68.13 to 121.08 Mg ha−1, of which 52.20–102.89 Mg ha−1 was stored in the soil and 12.09–20.15 Mg ha−1 in the biomass. In the non-reclaimed sites on BR, the total C storage was much higher, amounting to 523.14 Mg ha−1 (507.66 Mg ha−1 being in the soil), which was due to the geogenic coal content in the BR. However, the C storage in the biomass (15.48 Mg ha−1) and litter (5.91 Mg ha−1) was similar to the amounts obtained from the reclaimed sites. The number of species did not differ statistically significantly between the analyzed variants. On average, 14 species were recorded in the plots. The average Shannon–Wiener index (H’) value was higher for sites with BR (1.99) than TS variants on reclaimed plots (1.71). The lowest H’ value was for those plots with Robinia pseudacacia in the stand. One of the main implications of the obtained results for sustainable forestry is the perspective of using succession in the recovery of a disturbed ecosystem. We noted that woodlands from succession on BR are highly biodiverse, have high C sequestration potential, and do not require time-consuming reclamation treatments.

Novel method for determining the time coefficient [formula omitted] in Knothe’s function and disappearance time of deformation increase using SAR data

This paper presents a novel approach to determining the disappearance time of deformation increase after the conclusion of mining activity using Knothe’s time function and persistent scatterer interferometric synthetic aperture radar (PSInSAR). As a result, a method was proposed for determining a parameter of the function, the time coefficient c, using SAR data. The area of study was a strongly urbanised (city centre) post-mining region within the Upper Silesian Coal Basin (USCB), located in central-eastern Europe (Poland), which was characterised by intense hard coal mining that was concluded in 2015. The study analysed ground displacements generated directly after the conclusion of extraction as well as the time after which the rock mass assumes a relatively calm state. The obtained results were validated based on the results of classic geodesic measurements. The average time coefficient c determined by the developed method was 0.84, while the average time coefficient based on classic geodesic measurements was 1.01. So the theoretical disappearance time of deformation increase was, respectively, 5 years and 6 months and 4 years and 7 months. The research revealed that the developed method is helpful in determining the parameter in Knothe’s function and enables a more accurate definition of the disappearance time of deformation increase after the conclusion of extraction. This has great significance in the context of safety and the potential limitation of damage generated as a result of the negative influence of underground mining on the ground surface as well as for the spatial planning of post-mining areas.

Reservoir quality of Upper Cretaceous limestones (Ahlen-Fm., Beckum Member, Münsterland Cretaceous Basin): effects of cementation and compaction on the compactable depositional volume

AbstractThe Upper Cretaceous limestones unconformably overlie Upper Carboniferous coal-bearing lithologies and are studied to assess their effect on rising mine-water levels in the Ruhr mining district. Upper Cretaceous sedimentary rocks from the Münsterland Cretaceous Basin have previously been studied regarding their sedimentary structures and fossil content. However, understanding the petrophysical and petrographic heterogeneity in regard to sedimentary properties and their effect on fluid migration pathways is yet missing. Utilizing He-pycnometry, Klinkenberg-corrected air permeabilities, p-wave velocities, transmitted and reflected light analyses, point-counting and cathodoluminescence, we assess the petrophysical, geomechanical and mineralogical properties. Porosity ranges from 1.0 to 18.7% and permeability ranges from < 0.0001 to 0.2 mD, while p-wave velocity ranges between 2089 and 5843 m/s. Mechanical compaction leads to grain rearrangement, deformation of calcispheres, foraminifera and ductile clay mineral laminae. Above and below clay laminae, compaction bands of deformed calcispheres develop. Early diagenetic mineral precipitation of ferroan calcite in inter- and intragranular pores reduces porosity and permeability and influences geomechanical properties. An underestimated aspect of limestone petrography is the relationship of the original primary compactable depositional volume and the influence of compaction, deformation and cementation during early and late diagenesis on reservoir properties. The detrital dominated limestones show an originally high compactable depositional volume (CDV). Overall, reservoir qualities are poor and indicate the sealing potential of the studied lithologies. The Upper Cretaceous (Campanian) limestones thus may act as a barrier for increasing mine-water levels from dismantled, post-mining subsurface hard coal mines in the region. Graphical abstract

Post-mining related reactivation potential of faults hosted in tight reservoir rocks around flooded coal mines, eastern Ruhr Basin, Germany

The cessation of hard coal mining in the Ruhr Basin in 2018 marked the region's transition to the post-mining phase. Controlled mine water rebound induces changes in the subsurface stress conditions, as pore pressure increases locally. Presently, mine water rebound is observed in the eastern Ruhr Basin (water province “Haus Aden”) along with associated microseismicity. Furthermore, post-mining challenges might comprise the potential risk of fault reactivation, which is addressed in this study by conducting a fault slip assessment. Based on subsurface coal seam mapping data, a 3D structural model for the NE part of the “Haus Aden” water province has been constructed to serve as the basis for identifying the most vulnerable fault trends and types of the structural inventory. Slip tendency analysis, considering normal faulting conditions, revealed NW-SE to NNW-SSE trending normal faults to be most susceptible to reactivation. Probabilistic fault slip assessment, focused on NW-SE to NNW-SSE trending normal faults mapped within the “Heinrich-Robert” colliery, show no fault reactivation potential for a mine water rebound up to a level of 640 m below ground. Assuming hydrostatic conditions in the vicinity of the faults, friction coefficients are only partially exceeded for high differential stresses. In addition, a novel workflow is used to model the spatial variability of the frictional fault strength as input for a fault stability analysis, exemplified for a selected NNW-SSE trending normal fault. For considering hydrostatic pore pressure, results show that the fault consists mainly of stable, but also unstable, horizontally elongated patches. These findings question the conventional simplified approach of using a single constant friction coefficient for fault stability analysis.

Influence of Grain Size and Gas Pressure on Diffusion Kinetics and CH4 Sorption Isotherm on Coal

The paper presents research on the influence of grain size of selected coals and their structural parameters on the diffusion coefficient and methane sorption isotherms. Two coals from Polish hard coal mines, differing in the coal rank, were tested. Sorption isotherms for methane were determined. An unconventional sequence of pressures 0→0.1→0→0.5→0→1.5 MPa was employed to assess the speed of achieving sorption equilibrium at different pressures. The studies of CH4 accumulation kinetics were performed on various grain classes of the tested coals. Both the sorption capacity of coal and the diffusion coefficient proved to be highly sensitive to the experimental methodology. Critical measurement parameters in terms of determining the diffusion coefficient concerning the assumptions of the Crank model were indicated. The influence of the equivalent radius of coal grain on the process kinetics was demonstrated. The stepwise pressure increase factor was examined in the context of minimising the impact of sorption isotherm non-linearity on the results. The importance of the width of the grain class of coals was determined to reduce their maceral inhomogeneities. These factors are the most common reason that makes it difficult to quantitatively compare diffusion coefficient values.

Review of Research on the Impact of Changes Resulting from the Hard Coal Mining Sector in Poland on the GDP Value

Energy transition is one of the main objectives of the European Union. Significant changes will mainly affect countries in which significant modifications will have to be made to their energy sources. The process will involve high investment in infrastructure and additional costs of the transformation, such as reduced production (which may affect the GDP value) in the economic sectors involved in the process. The aim of this article is to provide the energy transition community, namely the national economy in general and those involved in planning for structural change in particular, with the key lessons and challenges in researching the impact of production changes in the mining sector. This article also shows the relevance of the mining sector in the economy. Within this area, particular attention is given to the following issues: the impact of economic sectors on the country’s GDP (gross domestic product); the identification of key sectors of the economy using the input–output method; the contribution of coal mining and the mining industry to Poland’s GDP; an analysis of changes in the structure of Poland’s economy using the input–output method; and the use of the input–output method in the context of changing/reducing the supply of economic sectors.

Nutrient uptake efficiency and stoichiometry for different plant functional groups on spoil heap after hard coal mining in Upper Silesia, Poland

Various plant functional groups (PFGs) used in the reclamation of post-mining heaps may differ in their nutrient uptake efficiency and thus in their effect on the ecosystem development. The effect of PFGs may be additionally modified by the applied reclamation measures such as e.g. topsoiling. In this study we compared the nutrient uptake efficiencies and plant stoichiometry for two PFGs (grasses and forbs) growing on the sites reclaimed by applying topsoil (TS) and unreclaimed sites on carboniferous bare rock (BR) in hard coal spoil heap in Upper Silesia (southern Poland). Basic soil parameters, including pH, texture, soil organic carbon, and nutrients (N, P, K, Ca, and Mg), were measured, and the aboveground plant biomass and nutrient content in plant tissue were determined. Forbs were characterized by a larger biomass and higher nutrient concentrations (except for P) than grasses. The TS treatment supported higher concentrations of N and P in plant tissues but not to the level ensuring more significant primary biomass production. The nutrient concentration and elemental stoichiometry in plant tissue indicated that N was the primary limiting element. However, the major growth limitation for N-fixing forbs was from P. Forbs were much more efficient in nutrient uptake than grasses, independent of the reclamation treatment. Therefore, they stimulate nutrient cycling in the restored ecosystems more than grasses.

Remote detection and monitoring of post-mining heat island

Underground hard coal mining activity in southern Poland has lasted more than 200 years. Among many factors related to mining and influencing the natural environment, the longest-active are coal waste heaps and tailings ponds. Several hundred objects are inventoried in Lower and Upper Silesia, of which 109 are located in the Lower Silesian Coal Basin (LSCB). These remnants of mining activity are built of gangue, waste coal, and coal silt (post-mining wastes). They cause environmental hazards, i.e., soil, air, groundwater, and surface water pollution in the storage area. They also tend to combust spontaneously, emitting enormous amounts of greenhouse gases into the atmosphere and increasing their neighborhood’s air, soil, and water temperature. Indigenous fires occur more than 20 years after the end of the waste disposal phase. The post-mining heat island (PMHI) phenomena, related to thermal activity development of the post-coal mining heaps and tailings ponds, is still under-recognition and research. Therefore, our study aims to improve and develop a methodology for remote detection and monitoring of heat islands resulting from coal mining operations to track the thermal activity of heaps and tailings ponds in LSCB from mines closure to 2023. The study used open satellite data from the Landsat program to identify and track post-mining heat islands over 23 years within the former mining area and verify the results within the borders of the inventoried heaps and tailings ponds. As a result, geospatial analysis on a time scale was carried out to identify post-mining hot spots. The self-heating intensity index (SHII) and the air temperature thermal indicator (ATTI) were calculated for identified and confirmed objects. SHII ranged between 0.00 and 10.07, and ATTI, on the other hand, varied from −12.68 to 25.18. Moreover, maps of the thermal activity of selected heaps were developed, the characteristics of the self-combustion phenomena were identified, and the remote detection of PMHI and its monitoring methodology was developed. The provided method can be used in the future to regularly monitor coal mining areas to prevent and identify hazardous hot spots and verify the maturity stage of the self-combustion processes.

Post-mining deformations in the area affected by the former “Siersza” Hard Coal Mine in Trzebinia (southern Poland)

Post-mining deformations in the area affected by the former “Siersza” Hard Coal Mine in Trzebinia (southern Poland)