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Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shallow and close-distance buried coal seam group is greatly affected by mining, and the phenomenon of multiple dimensions of air leakage and interconnection of channels is common in the coal mining face. Under the action of positive or negative pressure ventilation, a larger air leakage pressure difference is easily formed at both ends of the air leakage channel, resulting in an increasing air leakage volume in working face, the extension of the "three zones" in goaf, and the increasing risk of spontaneous combustion. This paper took Jitujing 12 coal in Daliuta Coal mine, a typical positive pressure ventilation mine, as the research object. It was concluded that the influencing factors of air leakage in shallow coal seam were as follows: air leakage channel formed by mining fissure, air leakage pressure difference formed by positive pressure ventilation, the ventilation mode and the natural wind pressure effect. The air leakage status and mode of the 12203 fully mechanized caving face under mining were investigated. It was concluded that the air leakage of the working face was mainly manifested as: surface collapse crack air leakage, face cutting, lanes and goaf air leakage in working face. Based on this, a comprehensive, multi-coverage and three-dimensional air leakage control technology was proposed. This technology was based on optimization of ventilation system, supported by grouting and spraying technologies in coal and rock fissure of roadway, coal pillar leakage risk control technology, and goaf end leakage risk control technology of working face, strengthened by local positive pressure leakage risk control technology, hydraulic flushing seam plugging technology and filling hole plugging technology, and based on the concept of foundation optimization, middle support and end treatment. The actual application was conducted in the 12203 caving face, and the air leakage volume reduced from 55-70 m3/min to 6-20 m3/min at the initial mining period, with a comprehensive reduction of 80.3%, which proved that this technology can effectively control air leakage, and provide technical reference for air leakage control in similar mine.

In order to study the overburden failure characteristics and surface subsidence law of shallow buried coal seam under the condition of double coal seam mining, based on the geological conditions of typical shallow buried coal seam in Yushenfu Mining Area, the numerical simulation method was used to analyze the overburden failure and surface subsidence characteristics under six different working conditions, and the physical similarity simulation experiment was used to verify. The results show that the failure mode of shallow buried coal seam is full-thickness cutting, and the mining-induced failure in the water-resisting layer in the retained coal pillar mining presents the “mud cover effect”. When the coal pillar is not retained, the two sides of the goaf form the development zone of separated cracks, and the cracks develop about 45° above the two sides of the goaf. The surface subsidence is stepped when the coal seam is mined. With the advance of the working face, the surface subsidence center moves forward continuously, and the influence of the weight of the aquifer on the surface subsidence is gradually reduced. The thickness of the coal seam is positively correlated with the surface subsidence value. There is stress concentration in the process of coal seam mining. The vertical stress in the overlying strata appears stress concentration area, stress relief area and stress concentration area successively along the direction of coal seam mining.

Aiming at the fact that the water-conducting fissures in the overlying rock may cut through aquifers and induce water inrush disasters by repeated mining of shallow-buried and short-distance coal seams in Shennan Mining Area, this paper adopts the methods of similarity simulation, numerical simulation and field drilling measurement to study the short-distance 1-2 coal and 2-2 coal mining overlying rock water-conducting fracture zone development law. When the 1-2 coal is fully mined, the height of the overlying fissure zone is about 50 m, and it is not connected with the upper quaternary loose pore water and the Jurassic weathered bedrock confined water; when the 1-2 coal and 2-2 coal are in repeated mining, the theoretical prediction of the water-conducting fault zone is about 136 m, the development height of the overburden fault zone is about 140 m according to the physical and numerical simulation, and the height of the water-conducting fault zone measured by the field borehole is about 135 m. The three are very consistent, and the fault zone is connected with the confined water of Jurassic weathered bedrock. The measures of dredging confined water from mining roadway to weathered bedrock of Jurassic at 300 m in advance working face are proposed. The field practice shows that no accident of water inrush and sand collapse occurs in the process of coal mining.

A comprehensive study was undertaken at Jiaozi coal mine to investigate the development regularity of ground fissures in shallow buried coal seam mining with Karst landform, shedding light on the development type, geographical distribution, dynamic development process, and failure mechanism of these ground fissures by employing field monitoring, numerical simulation, and theoretical analysis. The findings demonstrate that ground fissure development has an obvious feature of subregion, and its geographical distribution is significantly affected by topography. Tensile type, open type, and stepped type are three different categories of ground fissure. Ground fissures emerge dynamically as the panel advances, and they typically develop with a distance of less than periodic weighting step distance in advance of panel advancing position. Ground fissures present the dynamic development feature, temporary fissure has the ability of self-healing. The dynamic development process of ground fissure with closed-distance coal seam repeated mining is expounded, and the development scale is a dynamic development stage of "closure → expansion → stabilized" on the basis of the original development scale. From the perspective of topsoil deformation, the computation model considering two points movement vectors towards two directions of the gob and the ground surface is established, the development criterion considering the critical deformation value of topsoil is obtained. The mechanical model of hinged structure of inclined body is proposed to clarify the ground fissure development, and the interaction between slope activity and ground fissure development is expounded. These research results fulfill the gap of ground fissures about development regularity and formation mechanism, and can contribute to ground fissure prevention and treatment with Karst landform. [ABSTRACT FROM AUTHOR]

Coal seams were buried extremely shallowly in the trench slope area, which is prone to inducing surface cracks, seriously threatening the surface environment and mine safety production. The development of surface mining cracks varies at different locations in the trench slope area. In this research, we aimed to study the dynamic characteristics and laws of surface crack widths at different mining locations in the trench slope area and reveal the evolution mechanism of surface crack widths. Taking the 125,203 working face in Anshan Coal Mine in Shaanxi Province, China, as the geological prototype, we analyzed the full-cycle dynamic change law and planar distribution law of the surface crack widths in the trench slope area by combining the unmanned aerial vehicle remote sensing technology and field actual measurements and revealed the dynamic evolution mechanism of surface mining cracks in the trench area. The research results showed that the dynamic changes of surface crack widths varied at different locations of the slope. The surface crack width in the downslope area increased first and then stabilized with the advance of the working surface; the crack width at the bottom of the trench shows the dynamic change characteristic of increasing–decreasing–slightly increasing–stabilizing with the continuous advance of the working surface. The surface crack width in the upslope area showed the dynamic change of increasing–decreasing–stabilizing with the continuous advance of the working surface. Influenced by the surface morphology, the development mechanisms of surface mining cracks were different. The research results can provide practical guidance for selecting the best treatment time for surface cracks in different areas. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Taking the fire-threatened mines in the shallow buried coal seam of the Jurassic coalfield in northern Shaanxi Province as the research object, the high-resolution UAV visible light and thermal infrared dual-light low-altitude remote sensing, handheld infrared thermal imager, wind speed measuring instrument, spherical bladder sampler, bundle tube detection and sampling, gas chromatography, borehole temperature measurement, borehole peeping and other technical means are used to comprehensively carry out rapid exploration of hidden disaster factors in the sky, ground, hole and underground comprehensive mining work surface, closed wall, roadway and other potential air leakage channels. We systematically summarize the types and characteristics of hidden disaster factors in ground, hole and underground air leakage channels of shallow buried coal seam in Jurassic coal field in northern Shaanxi province, construct a four-in-one “sky-ground-hole-well” rapid investigation technology system for hidden disaster factors in shallow buried coal seam coal mine air leakage channels, and apply the technical system to the fire-threatened Dequan Coal Mine for the exploration, quickly determine the type of air leakage channel, spatial distribution characteristics, combine with the fire prevention project to achieve the rapid extinguishing of the fire area and the overall rapid control of the temperature of the hidden high temperature area of the coal mine to ensure the safe, green and efficient mining of the mine.

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the problem of the damage development process of overburden cracks and the prevention of floods in the working face with rich water layer under the influence of the main mining coal seam under the influence of the shallow buried thick loose layer. Taking the 31409 working face of Jinjie Coal Mine as the engineering background, and adopting the analysis method combining theoretical calculation and field measurement, it is obtained that the theoretical height of the overburden water-conducting fracture is 30.9 m to 53.9 m, and hydrological monitoring result indicates that the fissure zone during the mining process only penetrates the base rock aquifer and can not affect the stability of the loose aquifer. Water-rushing model is dominated by bedrock fissures and weathered fissures filled with water, and the groundwater level changes are characterized by “dynamic consumption & lateral replenishment”. The 3DEC software was used to establish a calculation model for the overburden disturbance calculation in the subsurface mining face, which showed that the evolution of the overburden water-transmitting fissures presents three zones: moving fissure area, fixed fissure development area and fissure development dynamic growth area. Based on the hydrogeological characteristics of aquifers near the coal seam, multiple layers, large thickness, high water head, etc., the “three-in-one” flood prevention and control technology has been implemented for the drainage hole layout method, the “zoning and grading” working face water inflow prediction method and the construction of special drainage measures. It effectively alleviates the water inrush hazard of underhand mining face under the rich water layer.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to solve the issues of uncertain overburden failure height and water loss at the Daliuta coal mine, the collapse characteristics of overburden and the development height of water-conducting fractured zone were studied by using physical modeling, FLAC 3D numerical simulation, and field observation, which were used to verify each other. In order to quantitatively analyze the distribution characteristics of fracture rate of overlying rock mass in goaf, the overburden collapse image was binarized. The results showed that: (1) the failure characteristics of overburden in goaf obtained by the three research methods were roughly consistent, and the reliability of the results was high. The overburden failure height of No. 5−2 coal with large mining height was 137.32–153 m, which was 20.8–23.2 times the mining height. (2) The repeated mining of No. 5−2 coal intensified the further failure of the disturbed rock mass in the No. 2−2 coal goaf. (3) In the horizontal direction of the goaf, the fracture rate of rock mass was distributed in the shape of "saddle". In the longitudinal direction of the goaf, the rock mass fracture rate decreased in a logarithmic function with the increase of the height from the mining coal seam. Overall, the conclusions are of engineering significance for accurately adopting water resources protection mining technology and reducing mine water inrush disasters. [ABSTRACT FROM AUTHOR]