Areas Of Underground Coal Mines Research Articles

Wastes in Underground Coal Mines and Their Behavior during Mine Water Level Rebound—A Review

Backfill materials of various origin and composition, abandoned machinery, oils, PCB, gallery support material and cables are the main wastes occurring in underground coal mines during the period of their abandonment. Bearing in mind that under increasing societal pressure most if not all underground coal mines are going to close sooner rather than later, it is important to understand the interactions of these waste materials with rising mine water during mine water level rebound to prevent adverse environmental effects, especially on surface and groundwater. To this end, the composition of mine water at decant points as well as the hydrogeochemical, temporal and spatial dynamics of mine water during rebound requires quantification. In the first part of this paper, an overview of waste materials in underground coal mines is presented. The second part focusses on the experiences gained in the Ruhr area, a closed underground coal mining region in western Germany, where mine water rebound has been ongoing for decades. In this regard, the mine water modeling program Boxmodell was applied during regulatory approval procedures to predict the hydrodynamics and hydrogeochemical development of the water rebound. The results of these investigations allow deep insights into the interactions of rising mine water with wastes as well as the complex chemical evolution of mine water and potentially occurring contaminants (e.g., PCB). The experiences regarding wastes in underground coal mines and the geochemical evolution of rising mine water gained in the Ruhr area can be utilized to support the planning of mine closure in currently still active underground coal mining areas worldwide.

Coal Mine Rock Burst and Coal and Gas Outburst Perception Alarm Method Based on Visible Light Imagery

To solve the current reliance of coal mine rock burst and coal and gas outburst detection on mainly manual methods and the problem wherein it is still difficult to ensure disaster warning required to meet the needs of coal mine safety production, a coal mine rock burst and coal and gas outburst perception alarm method based on visible light imagery is proposed. Real-time video images were collected by color cameras in key areas of underground coal mines; the occurrence of disasters was determined by noting when the black area of a video image increases greatly, when the average brightness is less than the set brightness threshold, and when the moving speed of an object resulting in a large increase in the black area is greater than the set speed threshold (V > 13 m/s); methane concentration characteristics were used to distinguish rock burst and coal and gas outburst accidents, and an alarm was created. A set of disaster-characteristic simulation devices was designed. A Φ315 mm white PVC pipe was used to simulate the roadway and background equipment; Φ10 mm rubber balls were used to replace crushed coal rocks; a color camera with a 2.8 mm focal length, 30 FPS, and 110° field angle was used for image acquisition. The results of our study show that the recognition effect is good, which verifies the feasibility and effectiveness of the method.

Large-Gradient Interferometric Phase Unwrapping Over Coal Mining Areas Assisted by a 2-D Elliptical Gaussian Function

Phase unwrapping (PU) is a key step in InSAR surface monitoring, which is directly related to the accuracy of the LOS displacement observations. Underground coal mining generally results in large gradient displacements, producing dense and aliasing fringes in interferograms. In this case it is challenging to accurately unwrap interferometric phases using traditional methods. This letter proposes an iterative algorithm to unwrap interferometric phases over underground coal mining areas. Firstly, differential interferogram is unwrapped by the minimum cost flow (MCF) method to obtain unwrapped phases at the edge of the mining subsidence basin. Then, a 2D elliptical Gaussian function, which could approximately describe the spatial shape of mining subsidence basin, is used to iteratively reduce the phase gradients of interferograms, so that residual wrapped phases at more pixel in subsidence basin can be unwrapped. The presented method was tested over Datong coal mine, China, based on 16 TerraSAR-X acquisitions. The result suggests that the accuracy of time-series displacements along the line-of-sight direction solved from the unwrapped phases using the new PU method is 1.1cm, indicating an improvement of 73.2% compared with that of using the traditional MCF method.

Quantitative assessment of the effect of mining subsidence on the health of native floras using remote sensing techniques

Remote sensing technique has been used in this paper to study the effect of underground coal mining subsidence on the health condition and growth pattern of the native vegetation. The study site was an underground coal mining area of Singareni Collieries Company Limited (SCCL), India. Mining was performed in 2001, and subsidence occurred in 2001–2002. Satellite imagery of the undamaged forest before the mining subsidence was compared with the affected forest after the mining subsidence. The changes in vegetation covered areas were analyzed based on digital image classification and vegetation index. The evaluation of vegetation changes was performed for the years 2000–2005 (period 1), 2005–2010 (period 2), 2010–2018 (period 3), and the entire study period of 2000–2018 (period 4), separately. It was observed that the dense vegetation area was reduced by 16.91% during period 1 (after 3–4 years of the occurrence of subsidence), while during the consecutive later periods of 2 and 3, it increased by 24.27% and 6.59%, respectively. During the entire period 4 of the study, dense vegetation was increased by 13.95%. This would be because of natural recovery and gradual stabilization of the native soil due to the absence of human interference in the long term of time. The sparse vegetation and non-vegetated area were changed by +14.22% and +2.68% during period 1, while they were changed by -15.36%, -7.91%, and -8.91%, +1.32%, during periods 2 and 3, respectively.

Spatial estimate of ecological and environmental damage in an underground coal mining area on the Loess Plateau: Implications for planning restoration interventions

Estimation of the ecological and environmental damage is viewed as an essential tool for effective decision-making in ecological restoration, especially involving high-intensity coal mining and high ecological vulnerability on the Loess Plateau, China. Using the Datong mining area on the Loess Plateau as a case study, we propose an integrated spatial estimation based on surface subsidence prediction, geographic information system, and field survey. The implications for regional ecological restoration are analyzed. Based on this inspection, the magnitude of ecological and environmental damage depended on a combination of risk factors, other than a single factor or evaluation target. Still, the geological hazard was the primary impact factor, especially surface subsidence as a result of underground mining. The results suggest that areas of severe, moderate, and slight damage accounted for 9.87%, 80.09%, and 10.04%, respectively. The methodology used was effective in determining the ecological and environmental damage that is consistent with the spatial distribution of subsidence. The proposed integrated estimation provides targeted measures for active, progressive, and passive interventions to improve and renovate the post-reclamation mining ecosystem and ensure sustainable planning in underground mining areas.

Identification of geomorphological hazards in an underground coal mining area based on an improved region merging watershed algorithm

To improve the automaticity for identifying geomorphological hazards in underground coal mining areas. An improved region merging watershed segmentation (Lab-RMWS) algorithm was proposed based on the Lab color space. It is generated by combining the classical watershed segmentation algorithm with the region merging algorithm. Additionally, the program was also developed in the VC++.net environment. To demonstrate its universality, a total of three experiments were performed using the Chinese GF-2 (Experiment I), Pleiades image (Experiment II), and QuickBird image (Experiment III). The results were comparatively analyzed with the interactive Self-Organization Data analysis (ISODATA), the maximum-likelihood classification (MLC), and the Luv color space based RMWS (Luv-RMWS). The results showed that the running time for the Lab-RMWS algorithm were, respectively, 112.83 s, 218.41 s, and 93.17 s for the target extraction, which could also achieve an integration of image segmentation and region merging. In comparison with the ISODATA and MLC methods, the time was reduced by more than 1 h, and the time efficiency was significantly improved. In the three experiments, the Lab-RMWS had the highest overall accuracy and kappa coefficient for the three experiments, with the values of 98.21% and 92.21%, 98.53% and 95.47%, and 97.59% and 89.18%, respectively. In general, Lab-RMWS had the best segmentation effect by considering the visual observation and evaluation indices. It is obvious that the proposed Lab-RMWS can be effectively used to identify the geomorphological hazards in underground coal mining areas.

Experience with the issue of seismic surveying over basalts

In some of Australia?s underground coal mining areas, near-surface basalt layers create problems for seismic reflection surveying. Affected mines have less confidence in their geological conditions and mine safety and productivity may be compromised. In order to gain insights and obtain potential solutions to this important problem, we have investigated seismic reflection and borehole vertical seismic profiling data from surveys at the North Goonyella Mine and the Moranbah South coal mine lease, which are both located in the Bowen Basin of Queensland. At North Goonyella, seismic velocities determined from the VSP survey indicate that the basalt is not fresh and up-going reflections from layers below the basalt are clearly seen. For the seismic reflection survey, advanced seismic data processing techniques such as pre-stack depth migration were able to improve the continuity of the coal seam reflections across the zone affected by the basalt. No special acquisition parameters were required. At Moranbah South, the problem with the basalts proved to be intractable. The basalts are hard and fresh, their total thickness is up 40 m, their width reaches 360 m and unconsolidated sediments lie between individual flows. The target coal seams are at depths less than 310 m and neither long-offset data acquisition nor prestack depth migration were able to produce satisfactory results. In general, the main issues for seismic surveying in basalt covered areas are (i) the generation of complex downgoing and up-going wavefields which are due to the strong impedance contrasts between the basalt and the surrounding strata, and (ii) the generation of incoherent scattered waves from inhomogeneities within the basalts and their rough margins. We have studied and confirmed these seismic phenomena through computer modelling.

Characterizing the spatial variability of soil particle size distribution in an underground coal mining area: An approach combining multi-fractal theory and geostatistics

Long-term underground coal mining activities results in severe surface deformation and land subsidence, altering soil physical properties significantly. Soil particle size distribution (PSD) is a fundamental physical attribute affecting many other soil properties. Therefore, understanding the variability of PSD is crucial to conduct targeted land rehabilitation. In present study, a novel method combining multi-fractal theory and geostatistics was advanced to characterize the spatial variability of soil PSD in a coal-mined subsidence area. Three independent field plots, i.e., one unmined plot (UMP), one subsided plots (SUP), and one reclaimed plot (RCP), in NO.3 Pingshuo Anjialing underground coal-mine in Shanxi province of China, were selected to perform this study. Four multi-fractal attributes of PSD of individual soil samples, i.e., D(0), D(1), Δα(q) and Δf(α), in three plots were calculated, and geo-statistics was employed to quantify the spatial variability of multi-fractal attributes of PSD. This combining method showed some advantages in characterizing the variability of soil PSD compared to single multi-fractal, single geo-statistics or traditional statistics, and it can characterize the spatial variability of overall PSD characteristics in detail, quantifying the spatial variability of soil PSD range, PSD concentration degree, PSD non-uniformity, and PSD non-symmetry. The soil PSD range, PSD concentration degree, PSD non-uniformity and PSD non-symmetry in this underground coal mining area didn't present a high spatial variability. Combining multi-fractal theory and geostatistics is an effective method to characterize the spatial variability of soil PSD in underground coal-mine area, and this method is universal and can be popularized and applied in other unmined areas.

Zoning method for environmental engineering geological patterns in underground coal mining areas

Environmental engineering geological patterns (EEGPs) are used to express the trend and intensity of eco-geological environment caused by mining in underground coal mining areas, a complex process controlled by multiple factors. A new zoning method for EEGPs was developed based on the variable-weight theory (VWT), where the weights of factors vary with their value. The method was applied to the Yushenfu mining area, Shaanxi, China. First, the mechanism of the EEGPs caused by mining was elucidated, and four types of EEGPs were proposed. Subsequently, 13 key control factors were selected from mining conditions, lithosphere, hydrosphere, ecosphere, and climatic conditions; their thematic maps were constructed using ArcGIS software and remote-sensing technologies. Then, a stimulation-punishment variable-weight model derived from the partition of basic evaluation unit of study area, construction of partition state-variable-weight vector, and determination of variable-weight interval was built to calculate the variable weights of each factor. On this basis, a zoning mathematical model of EEGPs was established, and the zoning results were analyzed. For comparison, the traditional constant-weight theory (CWT) was also applied to divide the EEGPs. Finally, the zoning results obtained using VWT and CWT were compared. The verification of field investigation indicates that VWT is more accurate and reliable than CWT. The zoning results are consistent with the actual situations and the key of planning design for the rational development of coal resources and protection of eco-geological environment.

Assessment and analysis of strata movement with special reference to rock burst mechanism in island longwall panel

This study presents a novel approach using theoretical analysis to assess the risk of rock burst of an island longwall panel that accounts for the coupled behavior of stress distribution and overlying strata movement. The height of destressed zone (HDZ) above the mined panel was first determined based on the strain energy balance in an underground coal mining area. HDZ plays a vital role in accurately determining the amount of different loads being transferred towards the front abutment and panel sides. Subsequently, based on the load transfer mechanisms, a series of formulae were derived for the average static and dynamic stresses in the island pillar through theoretical analysis. Finally, the model was applied to determining the side abutment stress distribution of LW 3112 in the Chaoyang Coal Mine and the results of ground subsidence monitoring were used to verify the predicted model. It can be concluded that the proposed computational model can be successfully applied to determining the safety of mining in island longwall panels.

A new prediction model for mining subsidence deformation: the arc tangent function model

Ground subsidence in underground coal mining areas causes environmental damage and creates hazards on the ground surface, which is long-term, widely distributed, and can lead to large-scale geological disasters. Achieving a high-precision method to predict mining subsidence deformation is very important for assessing environmental damage and countermeasures. In this paper, based on the “S”-type settlement curves of the monitoring points in the collapsed pit and the failure mechanism of rock strata on the goaf, the arc tangent function model was proposed and applied to the Taihe coal mine in Fushun, Liaoning Province, China. Using the Levenberg–Marquardt algorithm for nonlinear curve fitting of the data, the parameters of the model are obtained, and extending it in time, the prediction function will be obtained. Using different monitoring data to validate the model shows that the accuracy of the medium- and short-term forecasting is very good. With continuous updating of the monitoring data, the forecasting achieves higher accuracy and the function of dynamic track forecasting is achieved. A very high correlation coefficient was obtained (0.996) using all the available data from the monitoring point for the best-fit curve. This prediction model provides a reference for the evaluation and treatment of ground subsidence in the Taihe coal mining area.

Application of the spatial data mining module in analysis of mining ground deformation factors

Spatial data mining methods for example those based on artificial neural networks (ANN) allow extraction of information from databases and detection of otherwise hidden patterns occurring in these data and in consequence acquiring new knowledge on the analysed phenomena or processes. One of these techniques is the multivariate statistical analysis, which facilitates identification of patterns otherwise difficult to observe. In the paper an attempt of applying self-organising maps (SOM) to explore and analyse spatial data related to studies of ground subsidence associated with underground mining has been described. The study has been carried out on a selected part of a former underground coal mining area in SW Poland with the aim to analyse the influence of particular ground deformation factors on the observed subsidence and the relationships between these factors. The research concerned the uppermost coal panels and the following factors: mining system, time of mining activity and inclination, thickness and depth below the ground of the exploited coal panels. It has been found that the exploratory spatial data analysis can be used to identify relationships in multidimensional data related to mining induced ground subsidence. The proposed approach may be found useful in identification of areas threatened by mining related subsidence and in creating scenarios of developing deformation zones and therefore aid spatial development of mining grounds.

Dynamic subsidence simulation and topsoil removal strategy in high groundwater table and underground coal mining area: a case study in Shandong Province

Coal mining in high groundwater table areas causes many environmental issues. In China, such regions have three unique and significant characteristics, (1) multiple coal seams; (2) thick coal seams and (3) high groundwater, which lead to mine subsidence ponds. In the past, reclamation of disturbed land was carried out after subsidence stabilised. Such reclamation is a low-percentage of reclaimed farmland, and has high reclamation cost, difficult construction conditions, because of relatively flat terrain and the shortage of backfilling materials in flat topography. Therefore, salvaging the topsoil before it is submerged in water and reusing it while subsidence becomes stable would be a good way to improve the reclamation efficiency. This paper considers a longwall panel in Shandong province as a case study. Dynamic mining subsidence was simulated using mining subsidence prediction software. To illustrate subsidence development and its effects on farmland, the ground was first divided into cell size of 40 m along with pre-mining topography. The mining subsidence and water logging time for each cell were then calculated. Based on the simulations, the topsoil removal time, scope and depth of topsoil was determined. The salvaged topsoil could be reused subsequently, which would provide enough filling material to raise the percentage of reclaimed farmland, and reduce reclamation costs. The research benefits the development of concurrent mining and reclamation technology in underground mining sites, and promotes the synchronisation of exploitations and treatments.

An indicative method for determination of the most hazardous changes in slopes of the subsidence basins in underground coal mining area in Ostrava (Czech Republic)

Considering growing population and decreasing mineral resource reserves, the issue of undermining has been and shall remain very topical. This study aims to identify the mutual connections between mined out panels of a deposit and the final manifestations on the ground surface related to deep black coal mining. On the grounds of the identified connections, the study describes a method to simplify a common evaluation of undermined areas according to building site categories. Within the study, a demarcation of the areas was conducted in two localities in Czech Republic influenced by the effects of undermining in the Upper-Silesian Basin. In the allotment of the CSM Mine, an area unsuitable for founding structures was defined from the centre of the worked out workings to the distance of 175 m from the panel's edge, for which the corresponding break angle is 78.3°. Similarly, in the allotment of the Paskov Mine, an area unsuitable for founding structures was determined to the distance of 500 m from the panel's edge, for which the corresponding break angle is 50.2°. This demarcation may be implemented prior to deposit mining being aware of several physical-mechanical parameters of rocks in the deposit's overburden. Having mined out a particular section of a deposit, it is recommended to verify the values of break angle using the method described herein. The study may be applied as a relatively fast and effective method to evaluate future land use for planning.

Methane–air detonation experiments at NIOSH Lake Lynn Laboratory

The methane–air detonation experiments are performed to characterize high pressure explosion processes that may occur in sealed areas of underground coal mines. The detonation tube used for these studies is 73 m long, 105 cm internal diameter, and closed at one end. The test gas is 97.5% methane with about 1.5% ethane, and the methane–air test mixtures varied between 4% and 19% methane by volume. Detonations were successfully initiated for mixtures containing between 5.3% and 15.5% methane. The detonations propagated with an average velocity between 1512 and 1863 m/s. Average overpressures recorded behind the first shock pressure peak varied between 1.2 and 1.7 MPa. The measured detonation velocities and pressures are close to their corresponding theoretical Chapman-Jouguet (CJ) detonation velocity (DCJ) and detonation pressure (PCJ). Outside of these detonability limits, failed detonations produced decaying detached shocks and flames propagating with velocities of approximately 1/2 DCJ. Cell patterns on smokefoils during detonations were very irregular and showed secondary cell structures inside primary cells. The measured width of primary cells varied between 20 cm near the stoichiometry and 105 cm (tube diameter) near the limits. The largest detonation cell (105 cm wide and 170 cm long) was recorded for the mixture containing 15.3% methane.

Investigation of Dust Levels in Different Areas of Underground Coal Mines

Dust concentration levels in underground coal mines are of primary importance and have to be controlled to prevent pulmonary disease in miners. Different mining areas are exposed to different dust levels and to minimize the probability of occupational respiratory disease of coal miners, it is necessary to evaluate dust concentration in the different working areas. This study aimed to evaluate dust concentration levels in different areas of underground coal mines. Data obtained from the measurements in 1978–2006 were evaluated with the analysis of variance (ANOVA) and the Tukey-Kramer procedure. It was concluded that production areas had higher dust concentration levels; thus, production workers may have respiratory disorders related to exposure to coal dust in their work environment.

A Method for Estimating the Probability of Lightning Causing a Methane Ignition in an Underground Mine

During the past decade, several methane/air explosions in abandoned or sealed areas of underground coal mines have been attributed to lightning. Previously published work by the authors showed, through computer simulations, that currents from lightning could propagate down steel-cased boreholes and ignite explosive methane/air mixtures. The presented work expands on the model and describes a methodology based on IEEE Standard 1410-2004 to estimate the probability of an ignition. The methodology provides a means to better estimate the likelihood that an ignition could occur underground and, more importantly, allows the calculation of what-if scenarios to investigate the effectiveness of engineering controls to reduce the hazard. The computer software used for calculating fields and potentials is also verified by comparing computed results with an independently developed theoretical model of electromagnetic field propagation through a conductive medium.

Corona-Discharge-Initiated Mine Explosions

Strong circumstantial evidence suggests that lightning has initiated methane explosions in abandoned and sealed areas of underground coal mines. The Mine Safety and Health Administration (MSHA) investigated several of these occurrences within recent years. The investigated explosions occurred at significant depths, ranging from 700 ft to 1200 ft. Data from the national lightning detection network indicated a strong correlation between the times and locations of the explosions with those of specific lightning strikes. This paper proposes that corona discharge from a steel borehole casing is the most likely mechanism responsible for these ignitions. A recently investigated mine explosion and fire at a depth greater than 1000 ft was selected for this study. Computer simulations were performed, using data collected at the mine site. CDEGS/spl trade/ software from Safe Engineering Services & Technologies, Ltd (SES) and MaxwellSV/spl trade/ from Ansoft Corporation were used for the simulations.

Lightning propagation through the Earth and its potential for methane ignitions in abandoned areas of underground coal mines

Strong circumstantial evidence suggests that lightning has initiated methane explosions in abandoned and sealed areas of underground coal mines. The US Mine Safety and Health Administration investigated several of these occurrences within recent years. The investigated explosions occurred at significant depths ranging from 500 to 1200 ft. Data from the National Lightning Detection Network indicate a definite correlation between the times and locations of the explosions with those of specific lightning strikes. This paper addresses the question, "Can lightning cause potential differences capable of igniting methane-and-air mixtures at overburden depths at which underground coal mining occurs?" A mine depth of 600 ft was selected for this initial study. Computer simulations were performed, with and without the presence of a metal-cased borehole extending from the surface to the mine level. CDEGS software from Safe Engineering Services & Technologies, Ltd. was used for the simulations.

Development of a fire-resistant cardboard compressible block for use in stopping construction in underground mines

An engineering study was undertaken to develop a cost-effective compressible block for use in stopping construction in areas of underground coal mines exposed to convergent ground and roof conditions. A cardboard block consisting of 1.25-cm hexagonal cells with a nominal 0.4-mm face coating of intumescent paint was judged to be a viable solution to this problem and met the important performance characteristics of high fire resistance at low pressure differentials, low flame spread, resistance to air leakage, and relatively low compressive strength. These units may not perform well in areas of high humidity (above 90%). A special block, treated with 18% by weight of phenolic resin, displayed excellent resistance to moisture and adequate fire-resistance characteristics. It may be considered an attractive alternative to untreated blocks for use in mines experiencing high humidity (above 90%).