Datong Coalfield Research Articles

A novel geophysical method for fractures mapping and risk zones identification in a coalmine, Northeast, China

A novel approach for mapping induced fractures and associated lineaments has been introduced based on microseismic data, and thus their contribution towards identification, and prediction of the risk zones which may lead to a collapse or rockburst in a coal mine. By taking Tashan Coal Mine (TCM) in Datong coalfield of China as an example, the real-time microseismic data was acquired for a period of 7 months. The microseismic data was processed using standard processing schemes followed by source location and parameters estimation. The proposed approach utilizes microseismic events, trace them to map the induced fractures, and based on their network to interpret associated lineaments. Based on the configuration, geometry, and network, thousands of fractures were identified which vary in length. Regional lineaments have been interpreted based on the orientation of these fractures. The fractures and lineaments distribution were further correlated with computed microseismic energy distribution. The spatial distribution of microseismic energy helped in identification of a geological discontinuity (fault) that clearly separates the study area into northern and southern parts. The reactivation of this fault may pose significant threats to mass stability, life, and property. The northern half is characterized by more and short length fractures while southern by prolonged and fewer fractures. The upper northern half is dominated by high energy (≥50, 000 J), while the lower part is characterized by variable energy pattern (22,000 to 40, 000 J). It is inferred from the energy-lineaments correlation figure, the northern half describes relatively stronger rock type in comparison to the southern part suggesting different rock deformational behavior. The fractures and lineaments converging towards a single point define risk zones where future collapse or rockburst can be expected. This identification of risk zones provides a strong basis for the real-time prediction of future catastrophic hazards in the coal mines. This study may benefit global underground engineering researchers for hazards prediction and establishing of the early warning systems.

Distribution Characteristics and Formation Mechanism of Surface Crack Induced by Extrathick Near Horizontal Seam Mining: An Example from the Datong Coal Field, China

Under the mining condition of extrathick coal seam, the overburden moves violently, the surface is destroyed seriously, and the discontinuous deformation such as cracks is fully developed. Taking Datong mining area as an example, this paper studies and analyzes the development characteristics and generation mechanism of surface cracks in loose layer covered area and bedrock exposed area by means of field measurement and similar model experiment. In the bedrock exposed area, there is no main crack. The width, length, number, and step drop of surface cracks are relatively small. There are many cracks with the same scale and distributed evenly and parallel. However, in the loose covered area, the main cracks are mainly located above the open-off cut and the stoppage line side that is deviated from the working face. There are many secondary cracks around the main crack, with a large crack density and a few cracks in the outer edge of the main crack. Through research, it is found that three mining faces belong to the typical three-zone mining mode and the main fracture is consistent with the O-ring fracture distribution theory. This research’s results can provide theoretical and technical support for the follow-up land remediation and ecological restoration.

Application of Transient Electromagnetic Methods to the Safety Surveying of Coal Mines Production in the Datong Coalfield, China

There were a lot of water hazard accidents in coal mines, due to the lacking of effective methods for the coalfield surveying. The transient electromagnetic approach is one of such methods and was applied to examine the safety surveying of coal mine in the Datong coal mines during last two decades. Although there had been many successful cases of using the methods to the surveying of gobs water, meanwhile there were some difficulties to accurately detect and measure the size and location of gob water points, which still need to refine the advance of transient electromagnetic method.

Mineralogy, Geochemistry, and Genesis of Kaolinitic Claystone Deposits in the Datong Coalfield, Northern China

AbstractGray-black kaolinitic claystones of industrial value are abundant in Upper Carboniferous–Lower Permian coal-bearing strata of the Datong Coalfield of northern China. The main types are tonsteins and cryptocrystalline kaolinitic claystones, distinguished by the thinness and greater crystallinity of kaolinite in the former and by the presence of detrital illite and authigenic pyrite in the latter. In order to determine the formation history of these two types of kaolinitic claystone, the petrological, mineralogical, and geochemical characteristics of borehole samples from the Upper Carboniferous Taiyuan Formation which comprises siliciclastics and coal seams deposited in a coastal environment, were analyzed. In addition to kaolinite, the claystones contain subordinate illite, quartz, pyrite, anatase, feldspar, siderite, and calcite. The tonsteins and cryptocrystalline kaolinitic claystones have different sources, as shown by petrographic data, elemental ratios, and chondrite-normalized rare earth element (REE) patterns. The volcanic origin of the tonsteins is revealed by an abundance of volcanic quartz and vitric fragments as well as Al2O3/TiO2, Zr/Hf, and Nb/Ta ratios consistent with a felsic igneous source. Their REE fraction was derived from feldspars or micas of the parent rocks, and the fraction decreased with alteration of these minerals to kaolinite. The sedimentary origin of the cryptocrystalline kaolinitic claystones is revealed by an abundance of detrital quartz and illite grains derived from either granite or sedimentary upper crust, and by the total REE contents (ΣREE) and (La/Yb)N values which are consistent with granitic material. Their depositional environment was in a transitional (coastal) setting (as shown by intermediate Sr/Ba ratios) hosting an open acidic hydrologic system (as shown by high chemical index of alteration (CIA) values indicative of intensive chemical weathering) that was suboxic to anoxic (as shown by high U/Th ratios and trace-metal enrichment factors). The present chemistry of these claystones was thus controlled by a combination of parent rock type and diagenetic alteration.

Geochemistry of Carboniferous–Permian Coal from the Wujiawan Mine, Datong Coalfield, Northern China: Modes of Occurrence, Origin of Valuable Trace Elements, and Potential Industrial Utilization

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 μg/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al2O3/TiO2 and the figure of Zr/TiO2 vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 μg/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield.

Characteristics of an Altered Diabase Dike in a Coal Seam: A Case Study from the Datong Coalfield, Shanxi, China

Carboniferous–Permian coal seams in the Datong coalfield are intruded by Mesozoic magmatic dikes and sills. Our observations indicate that these dikes and sills have been seriously altered and have lost their original characteristics. Although this phenomenon has been mentioned in some studies, there is a lack of detailed research on the alteration mechanism. To fill this research gap, six dike samples were collected in this study to analyze their alteration characteristics and mechanisms. Petrographic analysis, scanning electron microscopy, and X-ray diffraction were used to determine the mineralogy of the altered igneous samples. The results suggest that the mineral alteration is associated with severe carbonation and clavization. The carbonation of mafic minerals is due to the release of CO2 generated from the coking of high volatile bituminous coals that may have occurred during the intrusive event. However, labradorite did not react with CO2. The water activity in the coal seam was enhanced by the dikes, and mafic minerals were converted into mixtures of chlorite and smectite group minerals. The water activity is especially high at the edges of the dike. Albite and clay minerals were formed due to the albitization of labradorite. Based on these effects, the dike can be divided into weak alteration, carbonation, and clavization bands. The alteration processes in the coal seam are described in detail in this work, and potential formation mechanisms are suggested.

Geochemical characteristics of No. 6 coal from Nanyangpo Mine, Datong coalfield, north China: Emphasis on the influence of hydrothermal solutions

This paper discusses the volcanic influence on the mineralogical and elemental geochemistry of No. 6 coal from Nanyangpo Mine in the Datong coalfield, north China. Sixteen samples (14 coal and 2 partings) were analyzed by different geochemical methods. The results revealed that the No. 6 coal is a medium–high volatility, highly calorific, bituminous coal with a low-ash and medium-sulfur content. The minerals mainly consisted of kaolinite, calcite, dolomite, and pyrite. In addition, traces of apatite, sphalerite, and anatase were also found. Calcite, dolomite, and pyrite in the coal samples were mainly derived from epigenetic hydrothermal solutions, whereas kaolinite and apatite originated from volcanic ash. Harmful trace elements including Pb, Cu, Mo, Tl, and Hg in the No. 6 coal samples were higher than those of common global coals. These harmful elements mainly occurred in sulfide minerals, which were probably influenced by hydrothermal inputs.

Automatic Coal and Gangue Segmentation Using U-Net Based Fully Convolutional Networks

Sorting gangue from raw coal is an essential concern in coal mining engineering. Prior to separation, the location and shape of the gangue should be extracted from the raw coal image. Several approaches regarding automatic detection of gangue have been proposed to date; however, none of them is satisfying. Therefore, this paper aims to conduct gangue segmentation using a U-shape fully convolutional neural network (U-Net). The proposed network is trained to segment gangue from raw coal images collected under complex environmental conditions. The probability map outputted by the network was used to obtain the location and shape information of gangue. The proposed solution was trained on a dataset consisting of 54 shortwave infrared (SWIR) raw coal images collected from Datong Coalfield. The performance of the network was tested with six never seen images, achieving an average area under the receiver operating characteristics (AUROC) value of 0.96. The resulting intersection over union (IoU) was on average equal to 0.86. The results show the potential of using deep learning methods to perform gangue segmentation under various conditions.

Strata movement and shield pressure analysis at Tongxin longwall top coal caving working face with extra-thick coal seam

Roof strata movement and shield pressure are two important factors that affect the production and efficiency of longwall top coal caving (LTCC) method in extra-thick coal seams. The performances of these two aspects can be very different from one mine to another depending on the roof strata conditions. In this paper, the geological conditions of the LTCC 8202 panel at Tongxin Coal Mine of Datong Coal Field are investigated. Low working face pressure was observed in the 8202 panel when mining the 20.6-m-thick carboniferous coal seam. This paper examines the causes of low mining–induced pressure at the LTCC 8202 working face, with both numerical simulations and in situ measurements. A finite element-discrete element software called CDEM is used for two-dimensional modelling of the #3–5 coal seam extraction at the LTCC 8202 working face. The numerical model simulates progressive collapse of the roof strata and computes shield pressure and convergence of the shield legs as the coal face advances. It is shown that the numerical model reproduces the periodical weighting phenomenon observed at the working face, which is created by the successive formation of composite cantilever beams in the lower hard rock layers, while voussoir beams form in the upper hard rock layers. As the upper roof voussoir beams interlock, they will tend to support part of the overlying strata, which ultimately lessens the pressure on the shield. A simple analytical model is developed to calculate the shield pressure under the composite cantilever beam structure. Finally, comparison of numerical simulation and analytical model results with measured shield pressure data from the field shows good agreement.

Influence of lamprophyre sills on coal metamorphism, coalbed gas composition and coalbed gas occurrence in the Tongxin Minefield, Datong Coalfield, China

Magmatic intrusions in coal-bearing strata can significantly change the physical and chemical properties of the intruded coal. Lamprophyre intrusions are extensive in coal seams 3–5 and 8 of the Carboniferous-Permian coal-bearing strata in the southeastern and southwestern regions of the Tongxin Minefield, Datong Coalfield, China. They appear primarily as sills of varying magnitudes, with thicknesses ranging from 0.15 to 23.51 m. In this area, coals can be classified as unaffected (normal geothermal gradient) and intrusion-affected. Unaffected coals are of high-volatile bituminous rank, with values of maximum vitrinite reflectance ranging from 0.7 to 0.9%, whereas intrusion-affected coals have values of maximum vitrinite reflectance ranging from 0.9 to 7.2%. A marked decrease in the degree of coalification can be observed with increasing distance from the lamprophyre intrusions. Near the intrusion-coal contacts, high-volatile bituminous coals have been thermally altered to form natural coke. The carbonate contents in intrusion-affected coals (0.2–46.1%) are significantly higher than those of the unaffected coal (0–2.0%). The coalbed gases of coal seams 3–5 and 8 are highly variable in both their molecular compositions and overall gas contents. Their CO2 volumes vary from 0.01 to 6.55 m3/t (daf); higher CO2 values are found in the coals affected by intrusions, and roughly decrease with increasing distance from the lamprophyre igneous intrusions toward the central region of the minefield. These variations in gas compositions are mainly related to magmatic activity. The coalbed gas contents in coal seams 3–5 and 8 range from 1.48 to 16.43 m3/t (on a dry, ash-free basis). The positive correlation observed between gas content and the ratio of CO2/CH4 + CO2 occurs only in intrusion-affected coals. Lamprophyre intrusions have negative effects on CH4 content in the study area. Since CO2 has a higher adsorption capacity than CH4, C2H6, and N2, the injection of gaseous CO2 derived from magmatic intrusions can effectively displace CH4-rich reservoir gas. In addition, there is a positive correlation between ash content and gas content on a dry, ash-free basis. Ash content is positively correlated with the ratio of CO2/CH4 + CO2 occurring only in intrusion-affected coals. Massive secondary carbonates that filled in the cleats act as small-scale impermeable seals, which provide a sealing effect both on gas contents and gas compositions during uplift.

In situ investigations into mining-induced hard main roof fracture in longwall mining: A case study

To better control strata behavior, it is necessary to understand the mining-induced hard main roof movement and fracture in longwall mining. In situ investigations were carried out on the 78,121 working face at the Jiangjiawan Coal Mine, Datong Coalfield, China. The longwall-mining-induced hard main roof movement and fracture were investigated by using digital panoramic imaging and a single-position extensometer. Then, geometric computational models were developed to estimate some parameters to describe the hard main roof fracture. Field observations indicate that after the mining of the 78,121 working face, the hard main roof was broken not only near the coalface regions but also near the side of the longwall panel. In accordance with in situ surveys and geometric computational models, the lateral fracture span, strike fracture span and final rotation angle of the broken main roof of the 78,121 working face were 15.56 m~23.97 m, 16 m~24 m, and 4.02°, respectively. In addition, field measurements found that the periodic roof weighting interval is equal to the strike fracture span and the lateral fracture span. This method provides a possible way to provide advance estimates of the above two parameters.

Concentrations and modes of occurrence of some potentially valuable and toxic elements in the No. 5 coal from the Yanzishan Mine, Datong Coalfield, Shanxi Province, China

In this study, the mineralogical compositions, concentrations and occurrence modes of the elements in the No.5 coal from the Yanzishan Mine were investigated, using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDS). The No. 5 coal is characterized by high ash yield content (mean 32.30%) and low sulfur content (mean 0.47%). The minerals are mainly composed of kaolinite, quartz and pyrite, with a small proportion of illite, apatite, siderite, sphalerite and Ti-oxide. Compared with the Chinese coals, the No. 5 coal has much higher percentages of SiO2 (mean 16.22%) and Al2O3 (mean 14.57%) than other major oxides. Compared with the world hard coals and Chinese coals, the No. 5 coal is enriched in some potentially valuable (Al2O3, Li, Ge, Zr, and Hf) and toxic (Be, As, Se, Cd, and Pb) elements. Lithium and Hf are mainly associated with clay minerals; Be, Se, and Zr mainly have both inorganically and organically affinities; As mainly occurs as a sulfide form in pyrite; Cd is incorporated in clay minerals; and Pb has an affinity for both clay minerals and organic sulfur. All the coal samples are characterized by weakly positive or no pronounced Eu anomalies, indicating that the rare earth elements and yttrium (REY) likewise originated from granite of the Yinshan Oldland together with injection of the low temperature hydrothermal fluids.

The impact of key strata movement on ground pressure behaviour in the Datong coalfield

In-situ investigations are the most direct and authentic approach for determining the law of strata movement. In this study, in-situ investigation was carried out to determine the law of fracture and movement of a key stratum. Four-point surface extensometer (FPSE) inside overlying strata and borehole camera observation were used in the overlying strata of a fully mechanized caving face of a super-thick coal seam in the Datong coalfield. The time–space correspondence between the fracture and movement of the key stratum and ground pressure in stopes was established in combination with observations of the ground pressure of the working face. Results show that the primary key stratum of the overlying strata is the main controlling stratum and its fracture and movement are the underlying cause of strong ground pressure behaviours, such as rib spalling, roof fall, and support crushing. The findings suggest that the primary key stratum can be weakened, and the energy release can be decreased by hydraulic fracturing, deep hole blasting, and other measures, thus relieving ground pressure behaviour. The research method of establishing the time–space correspondence between fracture and movement of the key stratum and ground pressure behaviours based on in-situ investigation can provide guidance for mining engineering schemes, such as exploring master control strata with strong ground pressure behaviour under similar conditions and determining a reasonable capacity for the support.

Field investigation of fractures evolution in overlying strata caused by extraction of the jurassic and carboniferous coal seams and its application: Case study

In multiple seam coal mining, the fractures induced by the mining of the lower coal seam may propagate to the goaf of the upper coal seam that is mined earlier. The fracture connection leads to the leakage of hazardous gas. To fully understand the gas leakage due to fracture evolution, the electromagnetic-based measurement system and the borehole televiewer were adopted in the panel No.8100 in Tongxin coal mine, Datong Coalfield, China. The coal seam thickness is 15 m and it was mined by top-coal caving method. The resistivity and fracture pattern in distinct zones of rock stratum were detected, and the correlation between them was explained clearly. We found that the fracture evolves in two stages as the panel working face advances, i.e., fracture propagation and fracture re-closure. The maximum height of fracture propagation is 150 m, in which the height of the caved and the fractured zones are 80 m and 70 m, respectively. These fractures start to be compacted and are re-closed at the distance of 80 m behind the working face. The extraction of the panel No.8100 results in the formation of a gas-bearing zone (GBZ) with separations and shear fractures rather than connecting the goafs of the carboniferous coal seam (CCS) and the jurassic coal seam (JCS). The GBZ is located in a region from 80 m to 150 m above the goaf and 80 m behind the working face. Based on the above findings, effective gas drainage approach is proposed to reduce the concentrations of the hazardous gases consisted of CH4 and CO. After gas drainage, the maximum concentrations of CH4 and CO drop to 0.5% and 16.63 ppm, with reductions of 53.7% and 33.9% respectively.

Geochemical and Mineralogical Characteristics of the Middle Jurassic Coals from the Tongjialiang Mine in the Northern Datong Coalfield, Shanxi Province, China

There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDS). No.12 coal is a low-medium volatile bituminous coal and is characterized by low ash yield content, low moisture content, and ultra-low sulfur content. Compared with Chinese coals, the Tongjialiang coals have slightly higher average percentages of MgO and P2O5, and lower average percentages of the other major oxides, including SiO2, TiO2, Al2O3, Fe2O3, CaO, MnO, Na2O, and K2O. Compared with the World hard coals, Be, Cr, Co, Ni, Ge, Sn, Ta, and W are slightly enriched in the Tongjialiang coals. The concentrations of Li, F, Sc, V, Cu, Ga, Se, Sr, Zr, Nb, Hf, Pb, Th, and U are close to the average values of the world’s hard coals. The minerals in No.12 coal mainly include quartz, kaolinite, siderite, and ankerite, along with smaller amounts of pyrite, illite, calcite, and rutile. The formation of syngenetic siderite in No.12 coal is related to the weathering of biotite in the gneiss of the Yinshan Upland. The modes of occurrence of ankerite indicate that the coals may be affected by the injection of low temperature hydrothermal fluids. It is noteworthy that a portion of epigenetic ankerite may be a product of metasomatism between syngenetic siderite and the epigenetic Fe-Mg-Ca rich hydrothermal fluids. The ratios of Al2O3/TiO2, REY (rare earth elements and yittrium) enrichment patterns, the modes of occurrence of siderite and ankerite, as well as the enriched lithophile and siderophile elements indicate that the No.12 coal may have originated from the Yinshan Upland and may also have been influenced by low temperature hydrothermal fluids that might have circulated in the coal basin.

Numerical Investigation into Evolution of Crack and Stress in Residual Coal Pillars under the Influence of Longwall Mining of the Adjacent Underlying Coal Seam

Longwall mining of the adjacent coal seam with the presence of residual coal pillars overlying the seam can result in abnormal strata pressure and severe overburden failure, which poses a significant threat to mining safety. The threat is mainly manifested in the form of intense coal or rock burst and hazardous interconnection between gobs. This study employed the universal distinct element code (UDEC) to investigate the microscopic failure mechanism of the overlying residual coal pillars under the influence of longwall mining of an adjacent underlying coal seam in Yuanbaowan coal mine, China. Using the Voronoi method, we innovatively visualized the evolution of cracks in residual pillars, revealed the mechanism behind the failure of pillars, and explored the evolution and distribution of abutment stress. Also, strata movement characteristics during underlying panel extraction have been surveyed. Based on the modeling results, effective measures are proposed to ensure safe mining under residual coal pillars. This study might provide a certain reference for safe extraction of multiple seams in Datong Coalfield, China, and also in the central and western Appalachian Basin, United States, where many mining activities are carried out under residual pillars.

Mineralogical and Geochemical Characteristics of Trace Elements in the Yongdingzhuang Mine, Datong Coalfield, Shanxi Province, China

Fifteen samples of No. 4 coal from the Yongdingzhuang Mine in Datong Coalfield were tested for their elemental compositions, modes of occurrence, and mineralogical compositions, using X-ray powder diffraction, X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, and scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The samples have low sulfur content (0.63%). The major minerals are kaolinite and quartz, followed by pyrite and anatase. Compared with averages for the Chinese coals, the percentages of SiO2 (15.11%), TiO2 (0.7%), and Al2O3 (10.39%) are much higher. In No. 4 coals, Li (62.81 μg/g), Be (6.94 μg/g), Zr (235 μg/g), Ga (17.04 μg/g), F (165.53 μg/g), Tl (1.93 μg/g), and Hg (0.34 μg/g) are some potentially valuable and toxic trace elements with higher concentrations than Chinese coals and World hard coals. Lithium and F mainly have kaolinite associations. With the exception of kaolinite, Li, and F also partly occur in anatase, gorceixite and goyazite. Beryllium largely occurs in anatase; gallium is mainly associated with kaolinite and to a lesser extent, with gorceixite and goyazite; zirconium is associated with kaolinite, gorceixite and goyazite; and thallium and Hg occur in in pyrite. Potentially valuable elements (including Al, Li, Ga, and Zr) might be recovered as value-added byproducts from coal ash. Toxic elements (e.g., Be, F, Tl, and Hg) might have potential adverse effects to the environment and human health during coal processing. In addition, the distribution patterns of rare earth elements and yttrium (REY) indicate that the REY in No. 4 coals originated from the granite of Yinshan Oldland, and natural waters or hydrothermal solutions that may circulate in coal basins.

Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

Longwall chock support failures seriously restrain the safety and high-efficiency of mining of extra thick coal seams, as well as causing a great waste of coal resources. During longwall top-coal caving (LTCC), the influential effect of the properties and the movement regulation of top-coal on strata behavior cannot be ignored, since the top-coal is the medium through which the load of the overlying strata is transferred to the chock supports. Taking Datong coalfield as an example, the mechanism of a chock support failure in the LTCC face was investigated. Research findings indicated that the hard top-coal and insufficient chock support capacity were primary reasons for chock support failure accidents. On account of the field-measured results, a new method to determine support capacity was proposed, which fully took the impact of the top-coal strength into consideration. The calculation revealed that the required support capacity had exceeded the existing production maximum, at about 22,000 KN. Since it was unrealistic to simply increase chock support capacity, other approaches, according to the theoretical analysis, were proposed, such as lowering the integrity and strength of the top-coal, and upgrading its crushing effect to weaken the support load effectively during the weighting period, which reduces the likelihood of chock support accidents occurring. Based on this, hydraulic fracturing for hard top-coal and optimization of the caving process (chock supports raised up and down repeatedly by manual operation before moving forward) were presented. The proposed solutions were successfully applied in LTCC-west8101 for subsequent mining and achieved substantial benefits. The above research provides valuable references and ideas for the control of strata behavior to ensure safe and highly efficient mining in extremely thick and hard coal seams with the LTCC method.

Using high-resolution UAV-borne thermal infrared imagery to detect coal fires in Majiliang mine, Datong coalfield, Northern China

ABSTRACTUnderground coal fires occur normally under inaccessible dangerous steep hills. As a light-weight and cost-effective equipment, unmanned aerial vehicles (UAVs)-based thermal infrared (TIR) imaging technique provides a choice to safely, timely and accurately map characteristics of coal fires which is difficult to realize using the conventional technologies. The colour images captured by UAV are used to generate a map of land cover types and estimate emissivity of ground features. TIR images are adopted to retrieve land surface temperature (LST) and thus generate orthophotos, which will be further used to recognize coal fire areas. The retrieved LST at night is validated with reference LST, and the results show yielding Root Mean Square Error (RMSE) is less than 1.03 K. The accuracy rate of identified coal fire areas at night time reaches as high as 92.78%, which is higher than that of daytime on 2nd October, 2016 and 5th October, 2016. In this research, the application of UAV-borne thermal imaging demonstrates a great potential to precisely and rapidly describe features of coal fires.

Analysis of internal pore structure of coal by micro-computed tomography and mercury injection

Micro-computed tomography (CT) technology and mercury injection were applied to study the internal pore structure of coal samples from the Gaojia kiln (Datong coal field) and Fulong bay coal mine. The results show that significant differences exist between different samples. The pore connectivity study shows that the number of maximum connective pore groups in coal samples 1, 2, and 3 is small. They are dispersed and confined to a small area with small permeability probability and low permeability. The maximum connective pore group percentage of coal sample 4 is higher, the porosity is larger, the permeability probability is higher and the permeability is better. By comparing the results obtained from micro-computed tomography and mercury injection studies, it can be concluded that the pore structure of coal consists mainly of open seepage pores. The volume of coal sample 4 accounted for the largest percentage of the total pore volume (up to 90%), whereas that of the closed pores is lower. Large amounts of methane gas can be extracted by predrilling during coal mining in Fulong bay and Gaojia kiln. This extraction may reduce the occurrence of safety accidents in coal mines. [Received: May 2, 2014; Accepted: December 3, 2014]