Coal Mines In China Research Articles

Research on the Design of Roof Cutting Parameters of Non Coal Pillar Gob-side Entry Retaining Mining with Roof Cutting and Pressure Releasing

With the increasing tension of current coal resources and the increasing depth of coal mining in China, Non Coal Pillar Gob-side Entry Retaining Technology has become a preferred coal mining method in underground coal mines. In the current study of the non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing, the theory and design of roof cutting under near-level conditions have formed a certain system. However, there is a lack of systematic research on the design of the roof cutting and the connection requirement of the cutting seam and other aspects about the inclined coal seam. Therefore, choosing the concrete representative target mines as the research foundation, using mechanics analysis, geometric analysis, numerical simulation and other means, on the basis of considering the change of mining height, this paper mainly studies about the effect of coal seam inclination on roof slit depth and angle, then get the three steps of the cutting height design, the three considerations of the roof cutting angle design and the connection rate requirement of the roof cutting. At last the key roof cutting parameters of the three target mines are calculated accordingly. Based on the existing research, this paper puts forward the concept and design method of roof cutting connectivity rate. The design system of roof cutting seam parameters of non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing is further improved, and the corresponding calculation method is deduced for the design of the key parameters of the inclined coal seam and the gently inclined coal seam, and proposing the second roof cutting scheme of the upper side gob-side entry retaining.

Mechanical Effect Analysis and Comparative Site Tests on Surrounding Rock with Different Bolt Anchoring Lengths and Pre-tightening Forces

Different bolt anchoring lengths and pre-tightening forces produce different mechanical and control effects on the surrounding rock. For clarification of the effects, a numerical comparative test is conducted to analyze the stress field distribution features of surrounding rock with different bolt anchoring lengths and pre-tightening forces. A high pre-tightening force quantitative exerting device is developed for high strength bolts with a function of automatic anchor retreat. With the device, a test on site is conducted at a typical roadway of Zhaolou Coal Mine in China; this test is on the comparative plans designed with different bolt anchoring lengths and pre-tightening forces; and the controlling effect is obtained on the surrounding rock in each supporting plan through the analysis of the test. This study shows it is conducive for the bolt pre-tightening force diffusing in surrounding rocks to exert high pre-tightening force and arrange a certain length of non-anchoring section; and it is conducive to form an effective bearing structure of anchored rocks. The new device is self-developed with independent intellectual property rights; and it can meet the requirement of roadway bolt support under high stress with many advantages such as large scale quantitative of pre-tightening force exerting and being easy to operate. Increasing pre-tightening force is an effective way to improve the control effect of surrounding rock; and an appropriate reduction of the bolt anchoring length will not significantly weaken the effect of the surrounding rock control, under certain conditions. The above conclusion can provide reference and experience for the anchoring support design and construction of the underground engineering.

Time trends and future prediction of coal worker\u2019s pneumoconiosis in opencast coal mine in China based on the APC model

BackgroundThe opencast coal mine is a specific mine differing from the underground mine. There are differences in the way into the ore body, the organization of production, transport technology and other aspects. This study aimed to describe the prevalence of CWP among ex-dust miners in opencast coal mines and estimate the incidence trend of CWP by APC model in the future.MethodsAll opencast miners who had been exposed to dust for at least 1 year in opencast mines were enrolled in this study. The database included demographic details, occupational history records with the date of dust exposure, physical examination records and pneumoconiosis diagnosis records. An age-period-cohort (APC) model has been carried out in order to explore the effects of the age, period and cohort on the prevalence of CWP among ex-dust opencast miners.Results8191 opencast miners were enrolled in the study, including 259 miners with CWP and 7932 miners without CWP. The incidence density of CWP would have an increasing trend in opencast mines from 2005 to 2024. The number of possible CWP patients predicted in this period was approximately 492. Of them, 275 miners could have suffered from CWP in 2005–2014 and 217 miners would suffer from CWP in 2015–2024 among the ex-dust opencast miners.ConclusionsThe APC model had a goodness of fit in predicting the incidence trend of CWP in opencast coal mines. By this model, we predicted that 492 opencast miners could be diagnosed as CWP from 2005 to 2024. Therefore ex-dust opencast miners cannot be ignored and they should have regular physical examinations and detection for CWP.

Surface-based radon detection to identify spontaneous combustion areas in small abandoned coal mine gobs: Case study of a small coal mine in China

Abstract In China, small coal mines refer to non-state-run coal mines with an annual production of less than 300,000 tons. The mining recovery rate of these small Chinese coal mines is low, and large amounts of coal remain in the gob. The mining seams of small coal mines are shallow, which induces extensive fissures between the gob and ground and provides easy pathways for air leakage. Consequently, long-term air leakage and oxygen supplies can result in spontaneous coal combustion in the gob, forming fire areas for many years. Determination of spontaneous combustion areas in the gob of small coal mines is difficult because fire sources are hidden underground and the geological data and roadway layout are poorly documented. Surface-based radon detection provides a fast, accurate, and low-cost method to identify spontaneous combustion areas in the gob of small coal mines. This study focuses on a small abandoned coal mine in Shanxi Province, China, using surface-based radon detection. Three abnormal temperature areas (A, B, C) and a potential abnormal temperature area (D) were identified. Drilling was subsequently performed to measure the temperature distribution in these areas. The results show that spontaneous combustion areas in small abandoned coal mine gobs can be successfully identified.

Research on reliability of scraper chain drive system

In the production practice, the key parts of scraper conveyor have a short life span and a high failure rate, which seriously restricts the production efficiency of coal mines in China. In order to ensure the high efficient and safe mining of coal resources, it is urgent to study the reliability of heavy scraper conveyor. With the development of deep and large coal mine in our country, the reliability of scraper conveyor is more and more high. In this paper, the structure of scraper chain transmission system is analyzed firstly, and then simulates the service age and reliability of the scraper chain system. Finally, it is concluded that when the scraper chain system transports different materials, the order of oscillation of the system reliability from long to short is lignite, coking coal, anthracite and gangue, and when entering the final plateau stage, the order of reliability from high to low is also lignite, coking coal, anthracite and gangue.

Asymmetrical Support Technology for Dynamic Pressure Roadway: A Case Study from Guotun Coal Mine in China

To form a kind of support technology that was universally applicable to all kinds of dynamic pressure roadways, This paper proposes asymmetrical support technology for dynamic pressure roadway. Firstly, the asymmetry characteristics of surrounding rock structure and stress distribution in dynamic pressure roadway were analyzed. The mechanism of asymmetric support technology for dynamic pressure roadway was preliminarily explored. Taking the 1303 dynamic pressure roadway in Guotun Coal Mine as the engineering background, the coal pillar width and support parameter were determined by numerical simulation and theoretical analysis. In the asymmetric support scheme, the roof bolts and the side bolts are respectively Φ20 × 2200 and Φ20 × 2000 mm, the spacing-discharge distance of roof bolts, coal pillar side bolts and coal body side bolts are respectively 800 × 900, 600 × 900 and 800 × 900 mm. Through field observation, the overall deformation of roadway surrounding rock supported by the asymmetric support scheme was not large and the deformation of the roof, coal pillar side and coal body side were basically equal. So, this asymmetric support technology can effectively control the deformation of surrounding rock in dynamic pressure roadway.

Prediction of coal-bearing strata characteristics using multi-component seismic data—a case study of Guqiao coalmine in China

The longwall mining method has been widely used in underground mining of coal seams. For longwall mining, the stability of coal-seam roofs and hardness of coal rocks in coal-bearing strata are particularly important. High-precision multi-component seismic exploration technology can obtain more parameters for characterizing coalbed reservoirs than conventional methods, and it is gradually replacing conventional P-wave technology in coalfield exploration. We have obtained multi-component seismic data from the central mining area of Guqiao Coal Mine, in the Huainan area, China. Using constraints from logging information, and seismic data, joint PP- and PS-wave inversion and interpretation have been performed. The coal seam 13-1, located in a Permian formation, was studied to determine the lithology of the coal-seam roof and floor, evaluate the stability of the coal-seam roof, and determine the hardness of coal rocks in coal seam 13-1. The distribution characteristics of lithology, roof stability, and hardness of coal rocks in coal seam 13-1 were also investigated. To achieve this, we used P- to S-wave velocity ratios to identify the lithology, evaluated the roof stability with parameters LambdaRho and MuRho, and used Young’s modulus to evaluate the hardness of the coal rocks. Our predicted results are in good agreement with the interpretative results from logging information, which shows the accuracy of our method. The joint PP- and PS-wave inversion and interpretation used in this paper can obtain more accurate information for evaluating coalbed reservoirs than conventional methods, which are valuable in assessing mine safety.

The Influence of the Backfilling Roadway Driving Sequence on the Rockburst Risk of a Coal Pillar Based on an Energy Density Criterion

The rockburst hazard has always been an important issue affecting the safety production of coal mines in China. The unreasonable sequencing of roadway driving can lead to the dynamic instability of coal pillars, which subsequently causes rockburst accidents in roadway backfilling mining engineering and poses a serious threat to the safety of the mines. Roadway backfilling mining technology is an effective approach with which to mine corner residual coal resources under buildings, railways, and rivers. An energy density criterion is established and programmed with FISH language using numerical analysis software for the rockburst risk evaluation of coal pillars. On this basis, a numerical simulation model is established based on four scheme types, namely, the sequential mining, one-roadway interval mining, two-roadway interval mining, and three-roadway interval mining schemes. The influence of the backfilling roadway driving sequence on coal pillar stability is investigated, and the change law of vertical stress and energy density factor of coal pillars in different driving sequences in roadway backfilling mining technology are analyzed. According to the research results, the maximum energy density factor value of 21,172 J/m4 for coal pillars in one-roadway interval mining is the lowest among the different schemes. Therefore, the one-roadway interval mining scheme is the optimal choice in roadway backfilling mining technology. The results can be treated as an important basis for the prevention and treatment of coal pillar instability and rockburst in roadway backfilling mining technology.

Microscopic Failure Mechanism Analysis of Sandstone Under Triaxial Compression

Mineral composition and microstructure changes under loading greatly influence the macroscopic mechanical strength of rocks. In this study, the chemical and mineral composition of sandstone from a coal mine in China were analyzed with energy dispersive spectrometry and X-ray diffraction. Triaxial compression tests of three sandstone samples with different compositions were carried out by using a servo-controlled rock mechanics testing system to obtain macroscopic failure characteristics and complete stress–strain curves. Fracture morphologies of the sandstone samples were observed by scanning electron microscopy (SEM), and the fracture origins, defects, grain size, pore structure and distribution, microfracture characteristics and grain boundaries were determined. Finally, the fracture mechanism of the rocks was analyzed, and the microstructure and fracture characteristics of three samples were obtained. The results showed that the stress–strain curve of samples under triaxial compression can be divided into four stages: microfractures compressed-closed, elastic deformation, plastic-failure and post-failure. Under triaxial compression, shear failure occurred in the samples, and the slip occurred along the plane of maximum shear stress. The SEM results showed grooves and steps on the fracture surface, where the debris was piled up in angular and granular shapes. Higher quartz and feldspar content is positively correlated with sample strength. There were some microcracks in the fracture surface of the clastic sandstone with higher hydrophilic clay minerals, which indicates the fracture was easily extended during the shear process. Thus, tensile fractures are more likely to be generated along the bedding plane, resulting in the low strength of clastic sandstone.

A process mining approach to improve emergency rescue processes of fatal gas explosion accidents in Chinese coal mines

Gas explosion has always been one of the major accident types in the coal mines of China, and reliable emergency rescue process is one of the key guarantees to minimize accident losses. As an emerging discipline to discover bottlenecks and position deviations of processes, process mining is widely used to improve various business processes in recent years. Nevertheless, scarcely does any research apply it to the field of coal mine emergency rescue to our knowledge. In this study, we apply the technique of process mining to domain of gas explosion accident emergency rescue in coal mines. 50 considerable and major gas explosion accidents, which occurred from the second half of 2006–2014 in Chinese coal mines, are selected as log data. The aspects of control-flow perspective, case perspective, helicopter view, organizational dimension and performance perspective are analyzed by process mining. In terms of control-flow perspective, the emergency rescue model is extracted by the inductive miner in ProM, correspondingly, conformance checking and comparison with real-life model have shown the validity of our work. Research also shows that the average length of cases is 23.72 events, and 60% of the cases are under the average length; 56% of the gas explosion accident emergency rescue processes last less than two days; emergency rescue headquarters, barmaster and medical staff share the highest centrality in social network of rescue; the rescue performance is more affected by accident grade, compared with the factors of accident site, region of coal mine and coal mine ownership.

A fuzzy comprehensive evaluation methodology for rock burst forecasting using microseismic monitoring

Rock bursts have become one of the most severe risks in underground coal mining and its forecasting is an important component in the safety management. Subsurface microseismic (MS) monitoring is considered potentially as a powerful tool for rock burst forecasting. In this study, a methodology for rock burst forecasting involving the use of a fuzzy comprehensive evaluation model was developed, which allows for a more quantitative evaluation of the likelihood for the occurrence of a rock burst incident. In the fuzzy model, the membership function was built using Gaussian shape combined with the exponential distribution function from the reliability theory. The weight of each index was determined utilising the performance metric F score from the confusion matrix. The comprehensive forecasting result was obtained by integrating the maximum membership degree principle (MMDP) and the variable fuzzy pattern recognition (VFPR). This methodology has been applied to a coal mine in China to forecast rock bursts. To select MS indices for rock burst forecasting using the fuzzy evaluation model, laboratory acoustic emission (AE) measurements of coal samples collected from the mine were performed. The model parameters were first calibrated using historical MS data over a period of four months, during which six rock burst incidents were observed. This calibrated model was able to forecast the occurrence of a subsequent rock burst incident in the mine.

Rock burst risk in an island longwall coal face by stress field

In many coal mines in China, skip-mining and the corner coal pillar will lead to the formation of an island longwall coal face (ILCF), which will induce a series of problems. Rock bursts pose a severe threat to miners and safe production in coal mines. Here, we used a mechanical model, theoretical calculations, seismic computed tomography, and energy density to explore the stress field distribution in an ILCF to obtain some pre-warning parameters. Based on elastic thin-plate theory, three cases of rock strata of ILCF were analysed to explore various stress fields (case 1: solid coal, case 2: two-sided goaf, and case 3: four-sided goaf). The stress reaches the peak value at the points of “a = b” in case 1, “a = 0.7b” in case 2, and “a = 1.4b” in case 3, respectively, which indicates high rock burst risk. In the case study, the test methods of seismic computed tomography and energy density were used on four ILCFs in Zhaolou Coal Mine (ILCFs 11301, 1307, 1305, and 1306). The stress field can be reflected by the three parameters: velocity distribution, velocity gradient, and stress concentration factor; and the energy density can indirectly reflect the accumulated damage of coal and rock mass and test two parameters of velocity distribution and stress concentration factor, which verifies the stress field in ILCFs, and assesses their rock burst risk.

Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China

Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China

Geomechanical Model Test and Energy Mechanism Analysis of Zonal Disintegration in Deep Surrounding Rock

With the decreasing of shallow resources, underground roadways of resources exploitation have reached into deep rock mass with high geostress. A series of new failure phenomena such as zonal disintegration phenomenon were discovered in deep surrounding rock, which is completely different from shallow caverns. To reveal the formation mechanism of zonal disintegration, the geomechanical model test and energy mechanism analysis of zonal disintegration were carried out respectively. Taking the deep roadway of Dingji coal mine in China’s Huainan coal mine as engineering background, a 3D geomechanical model test was carried out relying on the high stress 3D loading test system. The zonal disintegration phenomenon was observed, and the oscillation law of displacement was measured. Based on the strain gradient theory and continuum damage mechanics, the elastoplastic damage model was established. An energy failure criterion was proposed by principle of energy dissipation and release. The ODE45 function in Matlab software was used to solve the displacements and stresses of excavated model roadway. The analytical solutions the and the geomechanical model test were basically consistent. The applicability of theoretical model and energy failure criterion were confirmed to explain the mechanism of zonal disintegration and it can be used to provide theoretical support for the failure and supporting design of surrounding rock in deep underground engineering.

Experimental analysis on the optimal proportion of paste filler for a coal mine in China

Experimental analysis on the optimal proportion of paste filler for a coal mine in China

A Study of Positioning Approach of Underground Blasting Based on LS-DYNA Virtual Platform

The illegal exploitation of coal mine in China has been a threat to the national economy and the security of people's lives. It is necessary to efficiently monitor the illegal mining of coal, guarantee the safety of exploiters and restrain these unlawful activities. In order to determine the location of the blasting center, the theories of earthquake positioning were applied to get the location of underground blasting in this paper. The feasibility of these theories was testified by simulating the explosions on LS-DYNA virtual platform, and the optimal distribution method of test systems was obtained by comparing the results of different placement methods. Experimental results show that Multi-point circumferential distributed placement is most suitable for determining blasting center.

Extraction of the remnant coal pillar in regular and irregular shapes: A case study

With the increasing coal mining rate, many coal mines in China are facing the coal resource exhaustion problem. This paper presents a case study on extracting a coal pillar which was left in a longwall retreat mine, Wangzhuang mine, in China. The left coal pillars usually have boundaries of regular and irregular shapes, which result in complex stress distributions within the coal pillar. It is of great importance to study the stress distributions and to determine the roadway layout prior to extracting the left coal pillar. This study numerically analyzes the stress distributions in the left coal pillar, based on which the roadway layout and support techniques are proposed. The roadway stability were well maintained throughout the mining process and the mining safety and productivity were ensured. The left coal pillar in Wangzhuang mine was successfully extracted. This case study would be helpful for extracting the left coal pillar in the longwall retreat mines.

Prevention and control techniques & methods for water disasters at coal mines in China

Prevention and control techniques & methods for water disasters at coal mines in China

Nanoscale Pore Structure Characterization and Permeability of Mudrocks and Fine-Grained Sandstones in Coal Reservoirs by Scanning Electron Microscopy, Mercury Intrusion Porosimetry, and Low-Field Nuclear Magnetic Resonance

Porosity and permeability of two typical sedimentary rocks in coal bearing strata of underground coal mines in China, i.e., mudrocks and fine-grained sandstones, were comprehensively investigated by multiple experimental methods. Measured porosity averages of the helium gas porosity (φg), MIP porosity (φMIP), water porosity (φw), and NMR porosity (φNMR) of the twelve investigated rock samples range from 1.78 to 16.50% and the measured gas permeabilities (Kg) range from 0.0003 to 2.4133 mD. Meanwhile, pore types, pore morphologies, and pore size distributions (PSD) were determined by focused ion beam scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and low-field nuclear magnetic resonance (NMR). FIB-SEM image analyses showed that the mineral matrix pores including interparticle (interP) and intraparticle (intraP) pores with varied morphologies are the dominant pore types of the investigated rock samples while very few organic matter (OM) pores were observed. Results of the MIP and the full water-saturated NMR measurements showed that the PSD curves of the mudrock samples mostly present a unimodal pattern and nanopores with pore diameter less than 0.1 μm are their predominant pore type, while the PSD curves of the fine-grained sandstone samples are featured by a bimodal distribution. Furthermore, comparison of the full water-saturated and irreducible-water-saturated NMR measurements indicated that pores in the mudrocks are solely adsorption pores (normally pore size < 0.1 μm) whereas apart from a fraction of adsorption pores, a large part of the pores in the sandstone sample with relatively high porosity are seepage pores (normally pore size > 0.1 μm). Moreover, the PSD curves of NMR quantitatively converted from the NMR T2 spectra by T2Pc and weighted arithmetic mean (WAM) methods are in good agreement with the PSD curves of MIP. Finally, the applicability of three classic permeability estimation models based on MIP and NMR data to the investigated rock samples was evaluated.

Characterization and Remediation of Karst Collapse Columns for Mining Safety and Environmental Protection: A Case Study in Renlou Coal Mine, China

Karst collapse columns are unique collapse structures in karst terranes. Coal mining in China has exposed numerous such features of tens of meters in diameter and hundreds of meters in height. Hydraulically conductive collapses functioned as groundwater pathways between underground workings and aquifers, resulting in water inrushes during coal mining. Over the last 60 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment. Determination of locations and hydrogeological characteristics of the karst collapse columns are essential in preventing water inrush incidents through them. Advanced geophysical prospecting, directional drilling, aquifer testing and accompanied dye tracing are effective approaches to detecting and characterizing these structures. Five geophysical techniques consisting of both surface and underground geophysical surveys and directional drilling of three exploratory boreholes up to 986 m deep identified a concealed collapse feature of more than 135 m high in Renlou Coal Mine, China. The roof of the collapse feature was at approximately 785 m deep, and there was an open void of 1.5 - 2 m high at the top. Geotechnical properties, results from packer testing and tracer testing, monitoring of potentiometric pressures, and geochemical fingerprinting suggested that this collapse column was hydraulically conductive and still actively developing. Water in the confined thin-bedded limestone and Ordovician limestone aquifer that either overlies or underlie coal seams could flow into the underground working areas if this feature were not identified in advance but encountered during mining. A grouting program was designed and implemented to construct a water plug in the collapse that effectively cut off the hydraulic connections from the aquifers to the underground workings. Successful construction of the water plug in the collapse was confirmed by performance monitoring of the aquifers.