Study of a low-disturbance pressure-preserving corer and its coring performance in deep coal mining conditions

With the increasing depth of coal mining,the requirements for coring devices that maintain pressure are increasing.To adapt to the special environment in deep coal seams and improve the accuracy of testing gas content,a low-disturbance pressure-preserving corer was developed.The measurement of gas content using this corer was analyzed.The coring test platform was used to complete a coring function test.A pressurized core with a diameter of 50 mm was obtained.The pressure was 0.15 MPa,which was equal to the pressure of the liquid column of the cored layer,indicating that the corer can be successfully used in a mud environment.Next,a pressure test of the corer was conducted.The results showed that under conditions of low pressure(8 MPa)and high pressure(25 MPa),the internal pressure of the corer remained stable for more than 1 h,indicating that the corer has good ability to maintain pressure.Therefore,the corer can be applied at deep coal mine sites.The results of this research can be used to promote the safe exploitation of deep coal mines and the exploitation of methane resources in coalbeds.

Evaluation of roof cutting by directionally single cracking technique in automatic roadway formation for thick coal seam mining

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery,reduce roadway excavation and improve mining safety.In this method,roof cutting is the key process for stress relief,which significantly affects the stability of the formed roadway.This paper presents a directionally single cracking(DSC)technique for roof cutting with considerations of rock properties.The mechanism of the DSC technique was investi-gated by explicit finite element analyses.The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment.On this basis,the optimized DSC technique was tested in the field.The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock,thus,achieve directionally single cracking on the roadway roof.The DsC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway.Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Advancing respirable coal mine dust source apportionment:a preliminary laboratory exploration of optical microscopy as a novel monitoring tool

Exposure to respirable coal mine dust(RCMD)can cause chronic and debilitating lung diseases.Real-time monitoring capabilities are sought which can enable a better understanding of dust components and sources.In many underground mines,RCMD includes three primary components which can be loosely associated with three major dust sources:coal dust from the coal seam itself,silicates from the surrounding rock strata,and carbonates from the inert‘rock dust’products that are applied to mitigate explosion hazards.A monitor which can reliably partition RCMD between these three components could thus allow source apportionment.And tracking silicates,specifically,could be valuable since the most serious health risks are typically associated with this component-particularly if abundant in crystalline silica.Envisioning a monitoring concept based on field microscopy,and following up on prior research using polarized light,the aim of the current study was to build and test a model to classify respirable-sized particles as either coal,silicates,or carbonates.For model development,composite dust samples were generated in the laboratory by successively depositing dust from high-purity materials onto a sticky transparent substrate,and imaging after each deposition event such that the identity of each particle was known a priori.Model testing followed a similar approach,except that real geologic materials were used as the source for each dust component.Results showed that the model had an overall accuracy of 86.5%,indicating that a field-microscopy based moni-tor could support RCMD source apportionment and silicates tracking in some coal mines.

Fuzzy inference system using genetic algorithm and pattern search for predicting roof fall rate in underground coal mines

One of the most dangerous safety hazard in underground coal mines is roof falls during retreat mining.Roof falls may cause life-threatening and non-fatal injuries to miners and impede mining and transportation operations.As a result,a reliable roof fall prediction model is essential to tackle such challenges.Different parameters that substantially impact roof falls are ill-defined and intangible,making this an uncertain and challenging research issue.The National Institute for Occupational Safety and Health assembled a national database of roof performance from 37 coal mines to explore the factors contributing to roof falls.Data acquired for 37 mines is limited due to several restrictions,which increased the likelihood of incompleteness.Fuzzy logic is a technique for coping with ambiguity,incompleteness,and uncertainty.Therefore,In this paper,the fuzzy inference method is presented,which employs a genetic algorithm to create fuzzy rules based on 109 records of roof fall data and pattern search to refine the membership functions of parameters.The performance of the deployed model is evaluated using statistical measures such as the Root-Mean-Square Error,Mean-Absolute-Error,and coefficient of determination(R_(2)).Based on these criteria,the suggested model outperforms the existing models to precisely predict roof fall rates using fewer fuzzy rules.

TECHNICAL WAYS OF MINING COAL UNDER VILIAGES IN CHINA

Thisarticle discussesthe urgency andsignificane of mining coal under villages .On reviewingthe test methodsof mining coalunder villages inChina duringthe past 40years, the article also analyses the experiences obtained therefrom. Thearticle finally puts forward technical solutionsfor coal mining under villages and also pinpoints the problems to be solved.

Soil heavy metal(loid)s and risk assessment in vicinity of a coal mining area from southwest Guizhou, China

Total concentrations of arsenic, lead, cadmium, mercury, nickel, chromium, and copper in the soils from near a coal mine area in southwest Guizhou, China, were measured to evaluate the level of contamination, and the potential ecological risks posed by the heavy metals were quantitatively estimated. Results reveal that all heavy metals/metalloid exceeded the background values for soil environmental quality of heavy metals in Guizhou area. Geo-accumulation index(I_(geo)) showed that arsenic had the highest contamination level(I_(geo)=4) among the seven heavy metals/metalloid, and the contamination levels of mercury and lead were also relatively high(I_(geo)=3). Pearson correlation and cluster analysis identified that mercury, copper and arsenic had a relationship, and their presence might be mainly related to mining activity, coal and oil combustion, and vehicle emissions. Improved Nemerow index indicated that the overall level of heavy metal contamination in the studied area ranged from moderately–heavily contaminated to heavily contaminated level. Potential ecological risk index(R_I) analysis manifested that the whole ecological risk level ranged from high degree to very high degree(325.30≤R_I≤801.02) in the studied soil samples, and the potential ecological risk factors (E_r^i) of heavy metals/metalloid were as follows: Hg > As > Cd > Pb > Cu > Ni > Cr, and the E_r^i of Hg and As reached very high risk grade.

Time-lapse geophysical technology-based study on overburden strata changes induced by modern coal mining

To study the impact of modern coal mining on overlying strata and its water bearing conditions,integrated time-lapse geophysical prospecting integrating 3D seismic,electrical and ground penetrating radar method were used.Through observing and analyzing the geophysical data variations of all stages of pre-mining,mining and post-mining as well as post-mining deposition stable period,impacts of coal mining on stratigraphic structure and its water bearing were studied and modern coal mining induced stratigraphic change pattern was summarized.The research result shows that the stratigraphic structure and the water bearing of surface layer during modern coal mining have self-healing pattern with mining time;the self-healing capability of near-surface strata is relatively strong while the roof weak;water bearing selfhealing of near-surface strata is relatively high while the roof strata adjacent to mined coal beds low.Due to integrated time-lapse geophysical prospecting technology has extra time dimension which makes up the deficiency of static analysis of conventional geophysical methods,it can better highlight the dynamic changes of modern coal mining induced overburden strata and its water bearing conditions.

Environmental issues from coal mining and their solutions

The environmental challenges from coal mining include coal mine accidents,land subsidence,damage to the water environment,mining waste disposal and air pollution.These are either environmental pollution or landscape change.A conceptual framework for solving mine environmental issues is proposed.Clean processes,or remediation measures,are designed to address environmental pollution.Restoration measures are proposed to handle landscape change.The total methane drainage from 56 Chinese high methane concentration coal mines is about 101.94 million cubic meters.Of this methane,19.32 million,35.58 million and 6.97 million cubic meters are utilized for electricity generation,civil fuel supplies and other industrial purposes,respectively.About 39% of the methane is emitted into the atmosphere.The production of coal mining wastes can be decreased 10% by reuse of mining wastes as underground fills,or by using the waste as fuel for power plants or for raw material to make bricks or other infrastructure materials.The proper use of mined land must be decided in terms of local physical and socio-economical conditions.In European countries more than 50% of previously mined lands are reclaimed as forest or grass lands.However,in China more than 70% of the mined lands are reclaimed for agricultural purposes because the large population and a shortage of farmlands make this necessary.Reconstruction of rural communities or native residential improvement is one environmental problem arising from mining.We suggest two ways to reconstruct a farmer's house in China.

Waste-filling in fully-mechanized coal mining and its application

A fully-mechanized coal mining (FMCM) technology capable of filling up the goaf with wastes (including solid wastes) is described. Industrial tests have proved that by using this technology not only can waste be re-used but also coal resources can be exploited with a higher recovery rate without removing buildings located over the working faces. Two special devices, a hydraulic support and a scraper conveyor, run side-by-side on the same working face to simultaneously realize mining and filling. These are described in detail. The tests allow analysis of rock pressure and ground subsidence when backfilling techniques are employed. These values are compared to those from mining without using backfilling techniques, under the same geological conditions. The concept of equivalent mining height is proposed based on theoretical analysis of rock pressure and ground subsidence. The upper limits of the rock pressure and ground subsidence can be estimated in backfilling mining using this concept along with traditional engineering formulae.

Mechanism and control of water seepage of vertical feeding borehole for solid materials in backflling coal mining

To solve the problem of water seepage of vertical feeding borehole for solid materials,we established the fluid-solid coupling dynamic model of groundwater flowing in rock mass adjacent to the vertical feeding borehole.Combining with the engineering geological conditions,we built a numeral model to study the influence rule of the aquifer hydraulic pressure and seepage location of feeding borehole on the amount of seepage with fnite element numerical method.The results show that the nonlinear relationship is presented among the amount of seepage,the seepage location and aquifer hydraulic pressure.The higher the aquifer hydraulic pressure is,the closer the distance between seepage location and aquifer is,and the faster the harmful levels of aquifer will grow.In practice,we calculated the allowable seepage of feeding borehole by the optimum moisture content and natural moisture content of backflling materials,and then determined the protection zone of feeding borehole,so the moisture content of backflling materials can be controlled within the scope of optimum moisture content.

Effects of overburden characteristics on dynamic failure in underground coal mining

Dynamic failures, or ‘‘bumps", remain an imperative safety concern in underground coal mining, despite significant advancements in engineering controls. The presence of spatially discrete, stiff roof units are one feature that has been linked to these events. However, an empirical stratigraphic review indicates that no significant difference exists in the relative commonality of discrete units between bumping and non-bumping deposits. Instead an apparent relationship exists between reportable bumping and the overall stiffness of the host rock. However, this initial study is too simplistic to be conclusive; to weight the relative impact of changes in a single variable, such as the thickness or location of sandstone members, it must be examined in isolation—i.e., in a setting where all other variables are held constant.Numerical modelling provides this setting, and the effects of variability in a stiff discrete member in a hypothetical longwall mining scenario are investigated within the context of three stratigraphic ‘‘types",Compliant, Intermediate and Stiff. A modelling experiment examines changes in rupture potential in stiff roof units for each stratigraphic type as discrete unit thickness and location are manipulated through a range of values. Results suggest that the stiff-to-compliant ratio of the host rock has an impact on the relative stress-inducing effects of discrete stiff members. In other words, it is necessary to consider both the thickness and the distance to the seam, within the context of the host rock, to accurately anticipate areas of elevated rupture-induced hazard; acknowledging the presence of a discrete unit within the overburden in general terms is an insufficient indicator of risk. This finding helps to refine our understanding of the role of individual stiff, strong roof members in bumping phenomena, and suggests that a holistic view of overburden lithology and site-specific numerical modelling may be necessary to improve miner safety.

Changes of Precipitation Infiltration Recharge in the Circumstances of Coal Mining Subsidence in the Shen-Dong Coal Field,China

Coal mining subsidence is a universal environmental-geological problem in mining areas. By selecting the Shen-Dong coal mining subsidence area as the research field, this paper studies the changes in precipitation infiltration recharge in the circumstances of coal mining subsidence by means of field geological investigation and laboratory simulation experiments, which is expected to provide a scientific basis for eco-environmental restoration in the mining area. The results indicate that at the unstable stage of subsidence, three types of subsidence in the Shen-Dong mining area have positive effects on the precipitation infiltration recharge, and the type of full-thickness bedrock subsidence has the greatest influence. In the stable stage of subsidence, the precipitation infiltration process after long- term drought and the moisture migration in the aeration zone undergo three different stages： evaporation-infiltration before precipitation, infiltration-upward infiltration-infiltration during precipitation and evaporation-infiltration after precipitation. During a heavy rainfall infiltration process, the wetting front movement in fine sand, coarse sand and dualistic structure of fine-coarse sand consists of two stages： the stage of wetting front movement during precipitation, in which the wetting front movement distance has linear relationship with the depth, and the stage of wetting front movement after precipitation, in which the wetting front movement distance has the power function relationship with the depth. The wetting front movement velocity is influenced by the rainfall amount and the lithology in the aeration zone. However, as the depth increases, the movement velocity will decay exponentially.

Exploitation technology of pressure relief coalbed methane in vertical surface wells in the Huainan coal mining area

Exploitation technology of pressure relief coalbed methane in vertical surface wells is a new method for exploration of gas and coalbed methane exploitation in mining areas with high concentrations of gas, where tectonic coal developed. Studies on vertical surface well technology in the Huainan Coal Mining area play a role in demonstration in the use of clean, new energy resources, preventing and reducing coal mine gas accidents and protecting the environment. Based on the practice of gas drainage engineering of pressure relief coalbed methane in vertical surface wells and combined with relative geological and exploration en- gineering theories, the design principles of design and structure of wells of pressure relief coalbed methane in vertical surface wells are studied. The effects of extraction and their causes are discussed and the impact of geological conditions on gas production of the vertical surface wells are analyzed. The results indicate that in mining areas with high concentrations of gas, where tectonic coal developed, a success rate of pressure relief coalbed methane in surface vertical well is high and single well production usually great. But deformation due to coal exploitation could damage boreholes and cause breaks in the connection between aquifers and bore-holes, which could induce a decrease, even a complete halt in gas production of a single well. The design of well site location and wellbore configuration are the key for technology. The development of the geological conditions for coalbed methane have a significant effect on gas production of coalbed methane wells.

Quantitative evaluation of soil erosion of land subsided by coal mining using RUSLE

Based on a RUSLE model, we identified the key factors of the impact on soil erosion induced by coal min- ing subsidence. We designed a method for predicting/.S factors of a mining subsidence basin, using ana- lytical GIS spatial technology. Using the Huainan mining area as an example, we calculated the modulus of erosion, its volume and classified the grade of soil erosion for both the original area and the subsidence basin. The results show that the maximum modulus of erosion and the volume of erosion of the subsi- dence basin without water logging would increase by 78% and 23% respectively compared with the ori- ginal situation. The edge of the subsidence basin, where the land subsidence was uneven, is subject to the greatest acceleration in soil erosion. In the situation of water logging after subsidence, the maximum modulus of erosion would decrease if the accumulated slope length were reduced. This maximum mod- ulus around the water logged area within the subsidence basin is equal to that without water logging, while the total volume of erosion decreases. Therefore, mining subsidence aggravates soil erosion espe- cially at the edge of basins where water and soil conservation measures should be taken.

Case study on the extraction of land cover information from the SAR image of a coal mining area

In this study,analyses are conducted on the information features of a construction site,a cornfield and subsidence seeper land in a coal mining area with a synthetic aperture radar (SAR) image of medium resolution. Based on features of land cover of the coal mining area,on texture feature extraction and a selection method of a gray-level co-occurrence matrix (GLCM) of the SAR image,we propose in this study that the optimum window size for computing the GLCM is an appropriate sized window that can effectively distinguish different types of land cover. Next,a band combination was carried out over the text feature images and the band-filtered SAR image to secure a new multi-band image. After the transformation of the new image with principal component analysis,a classification is conducted selectively on three principal component bands with the most information. Finally,through training and experimenting with the samples,a better three-layered BP neural network was established to classify the SAR image. The results show that,assisted by texture information,the neural network classification improved the accuracy of SAR image classification by 14.6%,compared with a classification by maximum likelihood estimation without texture information.

Role of the different planting age of seabuckthorn forests to soil amelioration in coal mining subsidence land

To investigate the effects of seabuckthorn(Hippophae rhamnoides)on soil amelioration,using the space replacement method,soil physical and chemical indexes as well as the microorganism quantity and soil enzyme activities were analyzed.The results showed that:the soil bulk density of surface soil decreased and soil porosity and field capacity increased after afforestation with seabuckthorn.The plant was found to effectively reduce the soil pH,increase the soil conductivity,soil organic matters and available nutrients.Soil microorganism quantity,soil enzyme activities were both higher in 0-20 cm layer than in 20-40 cm layer.With the increase years of remediation with seabuckthorn,the quantity of soil microorganism and enzyme activities were increasing to a higher level 5 to 8 years later.Our study indicates that seabuckthorn can effectively improve soil physical and chemical properties,increase the quantity of soil microorganisms and enzyme activities,which is of great significance for the ecosystem restoration in mining areas.

Optimum location of surface wells for remote pressure relief coalbed methane drainage in mining areas

Based on engineering tests in the Huainan coal mining area,we studied alternative well location to improve the performance of surface wells for remote pressure relief of coalbed methane in mining areas.The key factors,affecting location and well gas production were analyzed by simulation tests for similar material.The exploitation results indicate that wells located in various positions on panels could achieve relatively better gas production in regions with thin Cenozoic layers,low mining heights and slow rate of longwall advancement,but their periods of gas production lasted less than 230 days,as opposed to wells in regions with thick Cenozoic layers,greater mining heights and fast rates of longwall advancement.Wells near panel margins achieved relatively better gas production and lasted longer than centerline wells.The rules of development of mining fractures in strata over panels control gas production of surface wells.Mining fractures located in areas determined by lines of compaction and the effect of mining are well developed and can be maintained for long periods of time.Placing the well at the end of panels and on the updip return airway side of panels,determined by lines of compaction and the effect of mining,would result in surface wells for remote pressure relief CBM obtaining their longest gas production periods and highest cumulative gas production.

Impact of coal mining on groundwater of Luohe Formation in Binchang mining area

Groundwater of Luohe Formation is the main water source for industrial and agricultural and residential use in Binchang mining area,which is one of the key elements to water conservation coal mining.However,few studies are available to document the enrichment characteristics and influence of underground coal mining on groundwater for the Luohe Formation.This study evaluates the changes of groundwater levels and spring flow caused by mining activities to explore the influence mechanism of coal mining on groundwater by comparatively analysing existing mining data and survey data combined with a series of mapping methods.The results show that the aquifer of Luohe Formation are gradually thinning south-eastwards,disappeared at the mining boundary.In the vertical direction,the lithological structure is distinct,due to alternative sedimentation of meandering river facies and braided river facies.According to the yielding property,the aquifer is divided into three sections,namely,strong water-rich section,medium water-rich section,and weak water-rich section,which are located in northwest and central part,southwest,and the rest part of the mining area,respectively.Mining of Tingnan Coal Mine since 2004 has caused a 3.16 to 194.87 meters drop in groundwater level of Luohe Formation.Until 2015,70.10%of the mining area undergoes a groundwater level drop larger than 10.00 meters.Another influence of underground mining is that the total flow from 34 springs in 8 southern coal mines of the area has decreased by 286.48 L/s with a rate of decrease at 46.95%from 2007 to 2017.The areas that groundwater level falls or spring flow declines are manly located in the mine gob areas.Results also indicate that the ratio of the height of water conducted fracture zone to the mining height in Binchang mining area is between 16.85 and 27.92.This may increase ground water flow in vertical direction,causing a water level in the aquifer system to drop and ultimately decreasing the flow from the springs.The research results will provide data and theoretical support for the protection of groundwater resources and water conservation coal mining of Luohe Formation in Binchang mining area.

Deformation and failure of a high-steep slope induced by multi-layer coal mining

During underground mining,accurate revelation on the deformation and failure mechanisms of a high-steep slope under multi-layer mining conditions facilitates the prevention and control of geological disasters in mines.Numerical simulation based on discrete element theory can be used to explore the characteristics and mechanism of action of deformation and failure of a slope under complex geological and multi-layer mining conditions.By utilising PFC2 D(particle flow code) software,the deformation and failure characteristics of a high-steep slope in Faer Coal Mine in Guizhou Province,China were investigated.Additionally,the mechanism of influence of different numbers of mining layers on the deformation and failure of the high and steep slope was elucidated.The result showed that after the goaf passed by the slope toe,multi-layer mining aggravated the subsidence and deformation of the slope toe:the slope toppled forward as it sank.The toppling of the slope changed the slope structures:the strata in the front of the slope were transformed from anti-dip to down-dip features.Extruded by collapsedtoppled rock mass,the slope toe and the rock mass located in the lower part of the slope toe generally exhibited a locking effect on the slope.Multi-layer mining degraded the overall stability of the slope,in that the total displacement of the slope was much greater than the total mining thickness of the coal seams.Based on the aforementioned research,ideas for preventing and controlling geological disasters during mining operations under a high-steep slope were proposed.

Predicting the height of water-flow fractured zone during coal mining under the Xiaolangdi Reservoir

It is very important to determine the extent of the fractured zone through which water can flow before coal mining under the water bodies.This paper deals with methods to obtain information about overburden rock failure and the development of the fractured zone while coal mining in Xin'an Coal Mine.The risk of water inrush in this mine is great because 40%of the mining area is under the Xiaolangdi reservoir.Numerical simulations combined with geophysical methods were used in this paper to obtain the development law of the fractured zone under different mining conditions.The comprehensive geophysical method described in this paper has been demonstrated to accurately predict the height of the water-flow fractured zone.Results from the new model, which created from the results of numerical simulations and field measurements,were successfully used for making decisions in the Xin'an Coal Mine when mining under the Xiaolangdi Reservoir.Industrial scale experiments at the number 11201,14141 and 14191 working faces were safely carried out.These achievements provide a successful background for the evaluation and application of coal mining under large reservoirs.