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To address the issues of large anomalous triangulations, invalid interpolations, and uneven boundary interpolations in kriging interpolation, we propose research on a coal seam modeling construction method based on improved kriging interpolation. The work methodology assumes that by introducing kriging interpolation and analyzing its problems, we improve the interpolation method via a local interpolation algorithm for large anomalous triangulations, an optimization algorithm for locally redundant interpolation points, and a nonuniform boundary adaptive local interpolation algorithm. These improvements allow the interpolation method to better reflect the variability and realistic nature of coal seams. The research results indicate that applying this method to the construction of the Dananhu No. 2 open-pit mine coal seam model has improved the issue of coal seam transition stiffness, such as abnormal large-area triangulation in areas with significant elevation differences. This approach appropriately reduces the memory space usage without altering the coal seam morphology (which saves approximately 27,000 KB of memory, equivalent to the space occupied by 4 out of 21 coal seams). It has also prevented inaccuracies in boundary line positioning and transitions caused by too low a density of points on the coal seam reserve boundary line, resulting in smoother model transitions at the boundaries that better align with the actual coal seam change trends, the error rate in coal quality estimation decreased by 62.69%. This study provides data support for mining planning and reduces costs. This method can be extended to the construction of all mine models.

This paper proposes a novel coal mining method (a diagonal collapse coal mining method), which can be applied in difficult‐to‐machine conditions due to the high variations of thickness and inclination angle of the coal seam. This method excavates coal by drilling up tunnels with a diagonal angle, and the transportation of coal in the face is carried by a chute without using special transport equipment. It is significant to determine the chute angle (diagonal angle) reasonably so that the transport is smooth and the remaining pillar is minimal. The relationship of the extraction rate with the variation of the angle of the tunnel is analyzed. The analysis showed that the recovery of coal seam below 15° was much lower. The flow of coal particles through the chute was simulated in an engineering discrete element method (EDEM) environment. The simulation was carried out between 15° and 20°, and the simulation results showed that coal particles can be carried freely at an angle of the chute above 15°. The results show that this method is best suited to apply in complex coal seams varying in inclination angles above 15°, and can be applied in coal seams varying in inclination angles below 15°, but it is preferable to take into account the economic index.

Extraction of gas (coalbed methane) produces clean energy and can ensure that coal mines maintain high-efficiency production. The currently available coal seam permeability enhancing technologies and modes have certain application restrictions. Therefore, a novel mode is proposed to promote gas extraction. This mode divides complex coal seams into tectonic regions and nontectonic regions based on geological structures. Then, the characteristics of different regions are matched with the advantages of different hydraulic technologies; thus, pressure relief technologies are proposed for tectonic regions, and fracturing technologies are proposed for nontectonic regions. The permeability of coal seams will be sharply increased without leaving unfractured areas. This mode will promote the effectiveness of gas extraction, shorten the extraction time, and ensure safe and efficient production in coal mines. A field application shows that this mode has a better effect than slotted directional hydraulic fracturing technology (SDHFT). The gas concentration and pure gas flow were increased by 47.1% (up to 24.94%) and 44.6% (up to 6.13 m3/min), respectively, compared to SDHFT over 9 months. The extraction time was reduced by 4 months. This mode reduced the number of times that gas concentration exceeded government standards during coal roadway excavation, and the coal roadway excavation speed was increased by 16% (up to 158 m/month).

Due to the large number of layers and different thickness of partings, the poor caving performance of top coal (CPTC) in thick coal seam with complex structure has always been an important problem affecting the top-coal recovery rate (TCRR) in the fully mechanized caving face. Based on the theory of coal-caving ellipsoid, a mechanical model of a long cantilever structure formed by the fracture of the thick parting crossing coal-caving ellipsoid was established, and the influence mechanism of the long cantilever beam structure on CPTC was revealed. Besides, a method to distinguish the influence of multi-layer partings on CPTC was put forward, and the influence of parting thickness, position and the number of parting layers on CPTC was obtained. The results show that the critical parting thickness hg increases with the increase of axial deflection angle θ, mining thickness h and volume weight of parting γg, and hg decreases with the increase of tensile strength of the parting Rt. The main influencing factors of hg can be ordered as follows: h > θ > Rt > γg. The position of the thick parting plays a controlling role in CPTC. The fundamental measure to improve CPTC is to reduce the cantilever beam length formed by the thick parting so that top coal above the parting can be caved. Based on this, the technical scheme of hydraulic fracturing for promoting top-coal caving was proposed and applied. During the initial mining period of the working face, TCRR was effectively increased from 45.99 to 77.18%.HighlightsThe influencing factors of the critical thickness of partings affecting the caving performance of top coal include h, θ, Rt, and γg.The layer of thick parting plays a controlling role in the caving performance of top coal of coal seam with multi-layer partings.A scheme of hydraulic fracturing to reduce the cantilever beam structure formed by the fracture of partings was proposed and applied.

Aiming at the complex conditions of the first shielded bolter miner in the actual work, the mechanical model of bolter miner cutting head was established. Based on cutting mechanism of the conical pick and the cutting head, the cutting head load and torque analysis model under complex coal seam were established. The dynamic characteristics of load and torque in the process of cutting head are analyzed under three different working conditions of cutting roof-coal layers, coal-floor layers and coal seam by finite element method. The results show that when the damage variable D=1, the coal-rock completely lacks the bearing capacity, and it forms arc-shaped crushing groove on the coal-rock. The large difference of torque between roof-coal layers and the roof-coal layers in the conical pick is 112N•m, which indicates that the cutting head has the best performance with cutting the coal seam first and then cutting the rock. In the process of excavation, the load fluctuation coefficient of cutting the coal-floor layers and roof-coal layers is about 1.2 times of that of the coal seam. The results can provide a reference for the efficient cutting and performance evaluation of the bolter miner.

Multi-seam upward mining is of considerable importance to improve the resource recovery rate and realize waste-free mining. Taking the Dianping coal mine in Shanxi Province as an example, the development height and evolution process of the overburden fracture after mining of the Taiyuan Group coal seam were studied by combining theoretical analysis, field measurement, and numerical simulation to verify the feasibility of upward mining (UM) of the multi-layer soft–hard alternate complex roof of Taiyuan group coal seam in Shanxi Province, China. A new method for determining the development height of overburden fractures (DHOF) is proposed on the basis of analyzing the fracture characteristics of rock strata with different lithologies. This method first calculates the fracture of key strata and then that of key soft rock strata controlled by key strata. The above method found that the DHOF of the Dianping coal mine is 52.5 m, and the field measurement and numerical simulation results are 53 and 49.7 m, respectively. The numerical simulation study found that after the upper and lower coal seams were mined, the rock fissures between the two seams were only connected to a small extent near the open-off cut, and most of the area still impermeable. Therefore, using the proposed method in UM is feasible after simple reinforcement of the rock seam in the vicinity of the open-off cut. In addition, on-site field measurements applied the borehole resistivity method to present a dynamic all-round view of the overburden fracture development process, and monitoring results indicate the existence of an unconnected fracture zone at the top of the fracture zones. Research results provide an important theoretical and technical basis for the prediction of the development height of the overlying rock fracture zone and the feasibility of UM in the Taiyuan coalfield, Shanxi Province.

Dynamic sublevel caving technology (DSCT) proposed by the researchers is one of effective methods to solve the problems of low top coal recovery, poor drawing balance and support stability in longwall top coal caving (LTCC) with large dip angle. To investigate the reasonable number of supports in a sublevel (N) and the top coal drawing mechanisms under DSCT, this research takes Panel 7401 in Zouzhuang Coal Mine as the geological background. Firstly, the optimal threshold value of N is theoretically analyzed, and the numerical simulations of drawing experiments under different Ns are calculated. The results show that when N = 3, the top coal recovery is the highest, the number of excessive drawing top coal at the upper end is relatively small, and the drawing balance is great, which is conducive to improving the resource recovery and safety management. With increasing N, the over-development of right top coal boundary towards the upper end increases, the range of coal ridge in the lower sublevel also gradually increases, while the strong force chain area at the upper end gradually decreases, resulting in the support stability becoming worse. In addition, the displacement of top coal at the upper end gradually increases with increasing N, and the permanent loss feature of residual top coal exists in the upper sublevel. The field top coal recovery under DSCT was measured finally, obtaining that DSCT can improve the top coal recovery by about 5% and promote the stability and working efficiency of the support. The research results have great theoretical and guiding significance for the high yield and high efficiency LTCC technology for thick coal seam with large dip angle.

Efficient gas extraction is important for reducing coal mine gas accidents and protecting the environment. A prerequisite for achieving efficient gas drainage is to clarify the evolution rules of mining fractures and the development characteristics of gas migration channels. In this study, aiming at the rock structure of coal seam composite roof, the evolution rules of gas migration channel in the mining process of the composite roof are analyzed, the multifractal characteristics of mining fracture development are discussed, and the most effective construction layer of high-level boreholes is quantitatively characterized. It has been found that the development process of gas migration channels can be divided into four distinct stages. During the mining of the working face, the Δ α that characterizes the uneven distribution of mining fractures in the multifractal spectrum shows a trend of increasing first and then decreasing and then stabilizing, and the Δ f α that characterizes the size difference of fractures in the multifractal spectrum shows a trend of decreasing as a whole, while the quotient of Δ α and Δ f α on the open-off cut side, and the working face side shows an increasing trend. Furthermore, the range of gas transition flow channel area in the composite roof is 9–17 times of mining height, the permeability in this range is concentrated in 6.92E-09 ~ 4.43E-07 m 2 . Notably, the hard rock strata within the range of 9–13 times of mining height are the best gas drainage levels. These results provide theoretical and technical support for gas drainage in coal mines.

The objective is to generate thermal energy from basic segments of the energy-chemical complex formed on the basis of borehole underground coal gasification with determination of its operation modes. The set engineering tasks were performed using, analytical studies, bench studies and field studies represented in research projects, patents, and feasibility studies concerning construction and scientific support while equipment operating of a pilot mine gasifier under the conditions of solid fuel seam gasification in the context of excessive fissuring of rock mass enclosing the gasifier. Studies of thermal and power indices of the station for coal gasification were carried out with the help of Information Program \"MTB BUCG\" (\"Material and Thermal Balance of Borehole Underground Coal Gasification\") developed by the researchers of the Department of Underground Mining and the Department of Chemistry (State Higher Educational Institution \"National Mining University\"). Besides, the Program was piloted using industrial gasifier at experimental mine \"Barbara\" (Katowice, Poland). Basic indices of coal gasification station depending upon a type of forced-draft mixture for an underground gasifier were determined. Studies concerning the efficiency of thermal energy generation were carried out using rocks enclosing the underground gasifier and generator gases being the basic heat generating segments of the energy-chemical complex for coal gasification being formed on the territories of operating coal mines or mines at the stage of their closure. Prospects of gasification and thermal energy generation using rock disposals of coal mines have been estimated. Modes of internal heat provision of heat-generating segments of the energy-chemical complex have been determined. Dependencies of heat-exchange distribution within roof rocks in the process of coal seam gasification depending upon the length of a reaction channel, zones of thermochemical reactions in it and methods of heat exchange have been obtained. Dependence of payback period of cogeneration plant in terms of underground coal gasification on electrical energy and gasification product (generator gas) has been determined. Graph of thermal energy generation in terms of different operation modes of basic segments of energy-chemical complex has been constructed. Technological scheme of a thermal utilizer has been developed. The plant provides possibility of thermal energy utilization in the process of coal gasification within the seam occurrence. Basic modes of thermal energy generation at the coal gasification station being a heat-generating segment of the energy-chemical complex have been determined.

The present research focuses on the mechanical properties and stress evolution of gas-bearing soft coal seams during drilling, which are affected by a multitude of complex factors such as high ground stress, gas pressure, and pre-existing fractures. In this study, a combination of PFC2D (Particle Flow Code in 2 Dimensions) numerical simulation and theoretical analysis is employed to investigate the borehole mechanics and fracture evolution characteristics under diverse complex conditions and to determine the factors influencing different forms of borehole failure in soft coal seams. The principal outcomes are as follows: (1) At a horizontal displacement of 0.1 m from the borehole orifice of the soft coal seam, a stress peak value of 13.9 MPa is attained; the peak value of the coal body contact force is 15.8 MPa; the peak value of the displacement is 0.008 m; and the porosity of the coal body around the borehole ranges from 0.14 to 0.35. (2) With an increase in the number of pre-existing fractures, the inclination progressively aligns with that of the pre-existing fractures. Maximum values of contact force (5.13–51.9 MPa), stress (3.19–37.2 MPa), shape dimension, and fracture angle (140–150°) are achieved under the highest lateral pressure coefficient and gas pressure (1.5 MPa). (3) The borehole energy is directly proportional to the number of pre-existing fractures, the lateral pressure coefficient, and gas pressure. The number of pre-existing fractures has the most significant impact on the damage degree, followed by the lateral pressure coefficient and then the gas pressure. (4) Two types of failure are identified: fracture-dominated failure, which is controlled by the geometric distribution of pre-existing fractures, and stress-dominated failure, wherein the failure zone gradually extends both upward and downward with an increasing lateral pressure coefficient.