Research on determining the safe mining depth in special geological conditions of Mong Duong coal mine

The displacement and deformation of strata due to underground mining is one of the factors that negatively affect the safety of production activities. The strata displacement and deformation depend on many factors such as mining geological conditions, safe mining depths, and mining technologies. The determination of the safe depths is important for calculating the size of safety pillars to minimize mineral loss. To date, there have been many studies to determine safe mining depths under normal geological conditions. However, not much research has been conducted to determine safe mining depths with special geological conditions such as many folds, breaks, faults, and under water-bearing objects. This research introduces a method to determine the safe mining depths for the reservoir set in special geological conditions with folds and excavating several seams under water bodies. The proposed method employs the principle of the similar geological zone theory to calculate the safe mining depths. The method is applied to the Mong Duong coal mine, with three coal seams numbered 5, 6, and 7 with the depth of 210, 180, and 136 m, respectively. The results of mining depths safe obtained H5= 240m, H6 =192m, H7= 136m, respectively.

Safe Mining Assessment of Artisanal Barite Mining Activities in Nigeria

Barite, used in mud formulation, is mined in several places to support the industry. However, there is insufficient literature on the downside of mining and associated hazards, especially in the artisanal barite mining sector. This paper contains three parts. The initial section reviews major causes of mining accidents and health hazards in Nigeria. The second section examines existing but weak institutional frameworks and policies for artisanal and small-scale mining (ASM) in Nigeria. In the third part, data from questionnaires and heavy metal contamination assessment are compared with health and environmental standards to identify and characterize hazards. It was observed that 54% had health challenges traceable to illicit drugs, and 54% were ignorant about the use of safety kits. The UV-Vis, AAS, and ICP-MS analyses confirmed lead, barium, zinc, copper, and iron in the water samples. Index of geoaccumulation (Igeo) and contamination factor (CF) show that water samples are moderate to highly polluted by Pb2+, Ba2+, and highly contaminated. The chronic daily intake assessment and health quotient analysis revealed that the accumulation of lead and barium is possible and can initiate chronic diseases in humans over a long time. Certain safe mining protocols and controls are recommended.

EVALUATION OF THE STABILITY OF A TEMPORARY PILLAR WHEN MIINING ORE HORIZONS WITH BACKFILLING AND CAVING

A method is proposed for mining thick and flat ore deposits at great depths in conditions of a decline in the value of extracted mineral raw materials. It is found that safe mining with solidifying backfill and caving is achieved by determining the parameters of stable spans of rooms, in place of which artificial supports and temporary ore pillars are formed. These pillars are recovered with a lag behind room-and-pillar mining by caving of ore and enclosing rocks. It is shown that, depending on the type of geomechanical model of geomedium and orientation of the initial natural stresses acting in the rock mass relative to the mining front, the field of application of the mining system is limited by the depth and parameters of excavation. Predictive areas of possible rock failure are determined applicably to rock masses with different degree of disturbance.

Critical Height of Unfilled Zone in Underlying Gob Piles

To address problems associated with mining above gob piles in the Chinese midwest mining area, a mechanic model for a coal pillar was established based on the displacement variation method. Additionally, the effect of critical unfilled zone height in the underlying gob (UZHUG) on the coal pillar was investigated through a 3DEC numerical simulation; fieldwork was conducted with a borehole televiewer to measure the UZHUG in the Yuanbaowan Coal Mine. The results indicated that the shear stress value and distribution layout in the coal pillar were affected by the UZHUG. The larger the UZHUG, the greater the shear stress and the wider the distribution scope, moving from two sides to the middle zone. Moreover, the larger the UZHUG, the smaller the maximum bearing capacity of the coal pillar, and subsequently, the greater the horizontal deformation of the coal pillar and roof convergence. The critical UZHUG is 2 m considering coal pillar deformation and stress transfer characteristics. Field measurements have confirmed that the UZHUG of 2 m ensured safe mining in the No. 6 coal seam. However, a second round of filling is needed when achieving a UZHUG of 4.4 m. This study serves as a reference for safe mining above gob piles.

Comprehensive technical support for safe mining in ultra-close coal seams: A case study

In order to mine the coal seam under super-thick hard roof, improve the utilization rate of resources and prolong the remaining service life of the mine, a case study of the Gaozhuang Coal Mine in the Zaozhuang Mining Area has been performed in this paper. Based on the specific mining geological conditions of ultra-close coal seams (#3up and #3low coal seams), their joint systematic analysis has been performed, with the focus made in the following three aspects: (i) prevention of rock burst under super-thick hard roof, (ii) deformation control of surrounding rock of roadways in the lower coal seam, and (iii) fire prevention in the goaf of working face. Given the strong bursting tendency observed in upper coal seam and lower coal seam, the technology of preventing rock burst under super-thick hard roof was proposed, which involved setting of narrow section coal pillars to protect roadways and interleaving layout of working faces. The specific supporting scheme of surrounding rock of roadways in the #3low1101 working face was determined, and the grouting reinforcement method of local fractured zones through Marithan was further proposed, to ensure the deformation control of surrounding rock of roadways in lower coal seams. The proposed fire prevention technology envisaged goaf grouting and spraying to plug leaks, which reduced the hazard of spontaneous combustion of residual coals in mined ultra-close coal seams. The technical and economic improvements with a direct economic benefit of 5.55 million yuan were achieved by the application of the proposed comprehensive technical support. The research results obtained provide a theoretical guidance and technical support of safe mining strategies of close coal seams in other mining areas.

THEORY AND PRACTICE OF DETERMINING THE CATEGORY HAZARD OF COAL MINES BY THE GAS FACTOR

A comparative analysis of the theoretical and practical definition of the category hazard of coal mines by gas factor based on experimental data obtained in real conditions of mining gas-bearing coal seams is presented. The mine's hazard category by gas factor is determined in accordance with the current regulatory document. The processing of experimental data obtained in field studies leads to contradictions in the requirements for the safe mining of gas-bearing coal seams. The necessity of changing the regulatory framework for predicting methane release and establishing the category hazard of mines by gas factor is substantiated, as well as the theoretical part of the research is experimentally confirmed and practical proposals are given to improve the requirements of regulatory documents for the safe mining of gas-bearing coal seams. The gas release from seven possible sources, the exposed surface of the working face, the undermined adjacent seams and their enclosing rocks, the overworked adjacent seams and enclosing rocks, the worked-out space of the stopped lavas, are accepted for consideration. The studies have shown that by removal the bottom from cut and the area of the mined-out space of the operated section and the wing of the mine field, taking into account the stopped longwalls, it is possible to predict the processes of rock displacement that determine the absolute gas release from the undermined sources.

ASSESSMENT OF FORECAST ACCURACY DANGEROUS PROPERTIES OF COAL LAYERS BY THE DEGREE OF METAMORPHISM OF SOLID FOSSIL COALS

In the normative base of Ukraine for the safe mining of coal seams, only five indicators of the degree of metamorphism are used to predict the manifestation of their hazardous properties during mining operations: mass release of volatile substances during thermal decomposition of coal without air (Vdaf) access to characterize coal; volumetric yield of volatile substances daf V V to establish the distinctive properties of anthracites; logarithm of electrical resistivity (lg); the thickness of the plastic layer (y) and the grade of coal (M) for predicting the outburst hazard of seams. When developing regulatory documents, it was assumed that these criteria for assessing the degree of coal metamorphism remain constant within one mine field. Their values, as mining operations show, are influenced by the location of the coal sampling site in relation to the distance from relatively large geological disturbances or the boundaries of the gas weathering zone. In most cases, the boundaries of mine fields are usually relatively large geological faults. The proximity of the locations of coal sampling points to them influences the obtained results of evaluating the properties of mine layers. Аdjusting indicators (Vdaf, daf V V , lg, y ,M) for individual mines on the possible impact of geological disturbances, the depth of the mining robot and the distance from the zone of gas weathering, according to the requirements of regulatory documents. For this reason, it is of scientific and practical interest to establish the possible ranges of change in the indicators of the degree of metamorphism of coal within the same mine layer. The results of research in this direction are relevant, as they are necessary to improve the regulatory framework for the safe mining of coal mines. A possible change within a separate mine field was considered using the example of the indicator Vdaf as the most studied at present. According to a specially developed methodology, the analysis involved data on 2193 mines from different coal basins. Most of them belong to the mines of the Donetsk basin (1773). The rest of the basins account for information on 460 mine layers, including data on 46 mine layers for the Lvov-Volyn basin.

IMPROVEMENT OF THE TECHNOLOGY OF DEVELOPMENT OF RESERVES OF THE EMISSION-HAZARDOUS FORMATION OF THE КРII STRATUM IN THE CONDITIONS OF THE EUROCHEM USOLSKIY POTASH MINE

This article presents the results of the authors' research on the construction of a pre-diction map with the division of an explosive potassium formation of the KPII stratum into haz-ardous and non-hazardous areas in the conditions of the mine field of the EuroChem Usolskiy potash mine, it is discovered that the decision rules developed for the other potash mines of the Verkhnekamskoye potash deposit are fundamentally unsuitable for the site concerned and re-quire revision, options of improvement the decision rule are proposed. Recommendations for safe mining operations, implicating a change of the existing mining technology, are presented at the end of the article.

STATISTICAL MODELS OF THE CLASSIFICATION INDICATOR OF THE DEGREE OF COAL METAMORPHISM FOR THE FORECAST OF DANGEROUS PROPERTIES OF COAL BEDS

Purpose: Based on statistical models of volatile matter yield during thermal decomposition of coal without air access (Vdaf) to establish probable relative errors of its measurement of absolute values which would allow to use the indicator with predetermined accuracy Vdaf as the primary classification criterion metamorphism of coal beds for the prediction of dangerous properties when led mining. Methods. It is used to create several sets of Vdaf values that have some features that are essential for their characteristics, followed by analysis of the statistical characteristics of these sets with the establishment of differences or similarities between statistical models. Results. Six sets of coal beds, which have different features of their creation according to the Vdaf criterion. There were from 114 to 412 variants in each set. As a general conditionally accepted set of 2091 coal beds of different coal deposits. For all (7) sets tested, the hypothesis of a normal distribution of variants according to Pearson’s criterion χ2 was tested. One part of the sets tested was close to the normal distribution of random variables, and the other did not correspond to the normal law. It is established that one of the reasons for the inconsistency of parts of the population with the normal law is the various errors in determining Vdaf depending on the absolute value of this indicator. In addition, individual samples from the conditionally general population have the same nature of the distribution of relative frequencies: with an increase in Vdaf to 10%, they decrease; in the range from 10 to 40% slightly increase; when Vdaf > 40% – again there is a decrease. Based on the close correlation dependences of the relative standard deviations of the volatile matter yield from the averaging curves, the validity of the possible use of Vdaf in engineering calculations of the forecast of dangerous properties of shafts only at its values more than 15-20% is proved. The possible influence of the distance of the coal sampling site to the boundaries of gas weathering zones and geological disturbances, and the high dependence of coal (more than 20%) on the additional error of Vdaf determination was also established. The established possible error values do not guarantee high accuracy of forecasting the dangerous properties of coal beds when using Vdaf as the main indicator of the degree of metamorphism. Improving the regulatory framework for safe mining of coal seams requires justification and application of other indicators of the degree of coal metamorphism. Scientific novelty: For the first time on the basis of statistical models, ambiguous possible errors in determining the yield of volatile substances during thermal decomposition of coal without air access and the inexpediency of its use to predict the hazardous properties of coal beds in mining. Practical significance. The necessity of using other indicators of the degree of metamorphism to improve the regulatory framework for safe mining of coal beds, which directly reflect the content and properties of coal in the process of geological transformations, has been proved.