矿业科学学报

Construction of digital twin system for intelligent mining in coal mines

Miao Bing, Ge Shirong, Guo Yinan, Zhou Jiaxin, Jiang Ersong

2022, 7(2): 143-153. doi: 10.19606/j.cnki.jmst.2022.02.001

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Abstract:
In order to fulfill the functions of comprehensive perception, real-time interconnection, analysis and decision making, autonomous learning, dynamic prediction and cooperative control, an overall framework of Digital Twin Smart Mining Workface was established. First, the digital twin smart mining face system was divided into 3 levels, and the functions and characteristics of each level were given.Secondly, based on the physical domain entities contained in the intelligent mining face, the data perception models of coal shearer, scraper conveyor, stage loader, crusher, hydraulic support, belt conveyor support, emulsion pump station and environment in the digital twin working face system were expounded in detail, and the collaborative constraint relationship among shearer, hydraulic support, coal flow transportation system, workface environment and equipment was analyzed in depth. Finally, the application scheme of the digital twin intelligent mining face system was designed. Based on the digital twin intelligent mining face system, the virtual-real mapping and real-time interaction between physical mine entities and digital mine twins could be realized, and the intelligent perception and cooperative control of digital twins could be performed, which provides a basis for improving the intelligent level of coal mining face.

The effect of freezing and thawing cycles on the mechanical properties and slope stability of the waste dump

Xu Wenbin, Wang Jiachen, Luan Maoxu

2022, 7(2): 154-165. doi: 10.19606/j.cnki.jmst.2022.02.002

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Abstract:
To investigate the shear strength evolution of soil-rock material in waste dump induced by freezing and thawing cycle (FTC), the shear tests are conducted by a self-developed direct shear apparatus, and the effect of FTCs on the shear strength degradation curve of soil-rock material is obtained. Furthermore, the inner microstructure of soil-rock material induced by FTC is analyzed by computer topography (CT)scanning testing.Finally, the stability of waste dump after and before freezing and thawing is compared. The results show that the shear and displacement curves of soil-rock material present strain softening during low normal loading pressure. However, the shear and displacement curve development trend changes from strain softening to strain hardening, and the shear dilatancy happens during loading process. As the FTCs increase, the strain hardening behavior becomes more obvious and the shear dilatancy effect is weakened. In addition, both the cohesion and friction angles decrease as the FTCs increase. When the number of FTC increases to 15, the decrement of cohesion and friction angle is 18.45 % and 9.42 %, respectively. The reason is mainly attributed to the dislocation and regroup of fine rock particles induced by freezing crack.The change in porosity of soil-rock material mainly happens within the initial 5 freezing and thawing cycles. The safety coefficient decrement of waste dump is approximately 7.6 % as the FTCs increase from 0 to 15. The results can provide guidance for waste dump in cold regions.

Research on classification and identification of mine microseismic signals based on deep learning method

Zhao Hongbao, Liu Rui, Liu Yihong, Zhang Yixiao, Gu Tao

2022, 7(2): 166-174. doi: 10.19606/j.cnki.jmst.2022.02.003

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Abstract:
In order to accurately identify mine microseismic signals, this paper proposes a VGG4-CNN deep learning network model suitable for identifying mine microseismic signals. The model is written in Python language and built based on the PyTorch deep learning network architecture framework. Based on the time-domain characteristics of the microseismic signals of 9 types of events such as rock fracture, blasting operations, and background noise in the mine production process, VGG4-CNN has realized the supervised learning training and classification recognition application of 3 835 sets of mine microseismic signal data. The research results show that the recognition accuracy of the VGG4-CNN neural network constructed in this paper is as high as 94 %. This model does not require denoising of the original waveform signal and is more robust than other models. The implementation can be performed by a medium-level GPU to meet engineering requirements.

Initial breaking characteristics of basic roof in trapezoidal stope of pseudo inclined working face

Zhang Shoubao, Li Qiang, Liu Zhigao, Huang Fulong, Wang Chao

2022, 7(2): 175-184. doi: 10.19606/j.cnki.jmst.2022.02.004

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Abstract:
When the stope is pseudo-inclined, the main roof of the goaf is basically non-rectangular. At this time, the fracture position and fracture rules of the goaf basic roof are different from that of the rectangular roof. To study the initial fracture characteristics of the basic roof of the pseudo-inclined stope, based on the mechanics theory of elastic thin plate. The initial failure mechanical model of right-angled trapezoidal basic roof plate structure was established, at the same time the bending formula of the right-angled trapezoidal thin plate was deduced, the fracture position and fracture rules were analyzed; at the same time According to the finite difference principle, the principal stress extreme value and position characteristics of the basic roof were analyzed, and the theoretical deduction results were verified. The results show that the internal force distribution of a right-angled trapezoidal thin plate with four sides fixed is roughly similar to that of a rectangular thin plate, but on four borders the position of the main bending moment extreme value is different from that of the rectangular thin plate. The latter are all located in the centre, while the formerly on the four sides of the thin plate moves to one side in the counterclockwise direction as a whole, and the Initial Breaking of the basic roof is inclined "O - X" type.

Study on estimation method of methane permeability in coal

Li Wenrui, Zhao Yaoyao, Wang Dengke, Liu Peng

2022, 7(2): 185-192. doi: 10.19606/j.cnki.jmst.2022.02.005

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Abstract:
The gas flow path in coal body is mainly composed of slits and pores, which is a typical dual gas flow path structure. Generally, in order to quantify the apparent permeability of gas transport in different scale flow paths, mathematical models of permeability are established using the pore or slit structure of single flow path. With the development of microstructure characterization technology, the characterization of slits and pores in real coal is more accurate, and the permeability model based on single flow path is obviously not accurate enough. Therefore, in this paper, the micron scale gas flow path is simplified into two geometric forms of slit and pore. High-precision CT technology is used to obtain the volume proportion of pore and slit structure in the total gas flow path, namely pore porosity and slit porosity. Then, the parameters are substituted into the statistical distribution model of permeability, and the overall apparent permeability with slits and pores is obtained. Finally, the calculation results of apparent permeability of single flow path pores-based model, slits-based model and the dual flow path pore-slit-based model are compared and analyzed. The results show that the slit-based apparent permeability model overestimates the actual apparent permeability, but the pore-based apparent permeability model underestimates it, and the mixed pore-slit-based permeability is in between. From the mean value of relative deviation of apparent permeability calculated for single gas path structure and dual gas path structure, the mean value of relative deviation of pore-based apparent permeability is no more than 50 %, which is closer to that of the real dual flow path pore-slit-based apparent permeability.

A statistical model of size effect on concrete tensile and compressive strength

Wang Zhibin, Yang Liyun, Qian Guian, Li Qintao, Xu Huidong

2022, 7(2): 193-199. doi: 10.19606/j.cnki.jmst.2022.02.006

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Abstract:
In order to study the relationship between the tensile and compressive strength of the concrete commonly used in engineering and the size of specimen, a statistical model of the size effect on concrete strength was established based on the generalized weakest chain formula proposed by Lei recently, assuming that the distribution of the internal defects in concrete follows the uniform distribution or the Poisson distribution. It realizes the prediction of the strength of small-scale concrete specimens to the strength of full-scale members under the condition of a given failure probability. The analysis of concrete strength data from the three published cases shows that: Under the assumption of uniform distribution of defects, the statistical method of size effect can well reflect the relationship between the tensile strength and size of ordinary concrete and RPC.The internal defect distribution of RPC concrete is closer to a uniform distribution, and the relationship between its compressive strength and size can also be described by the statistical method of size effect.

Analysis of roof bearing characteristics and coal pillar stability of cemented backfill field

Xu Bin, Li Yongliang, Lu Bin, Li Jin

2022, 7(2): 200-209. doi: 10.19606/j.cnki.jmst.2022.02.007

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Abstract:
In order to study the bearing characteristics of the roof and the coal pillar stability of continuous mining and continuous filling cemented filling field, a numerical analysis model based on FLAC^3D is established to analyse the alternate bearing characteristics of the roof, study the conversion law of the primary and secondary bearing structures of the roof, and reveal the stress release and deformation law of the coal pillar. Based on the difference of the constraint conditions on both sides of the coal pillar, a mechanical model of the stress distribution of the coal pillar is established, and the influence law of the stress concentration coefficient, temporary support strength, burial depth and other factors on the ultimate bearing width of the coal pillar is obtained.By establishing the numerical analysis and simulation of the synergistic bearing of coal pillar and filler, the influence of the width of filler on the bearing characteristics of coal pillar is revealed. The study shows that: the bearing structure of the mine roof changes with the advancement of the working face, and the coal pillar is the main bearing structure during the co-bearing stage of the coal pillar and the filling body, and the filling body gradually transitions to the main bearing structure as the coal pillar is gradually extracted; the width of the stress equilibrium zone of the coal pillar is inversely proportional to the strength of the temporary support, and is positively proportional to the burial depth of the working face and the stress concentration coefficient, increasing the strength of the temporary support can significantly reduce the fragmentation zone of the critical surface. The increase in the width of the filling body can effectively control the stability of the coal pillar, and its main function is to reduce the force on the coal pillar while playing a role in restraining the lateral deformation of the coal pillar. In Haoyuan coal mine, by increasing the strength and filling rate of the filling body and enhancing the restraining effect of the filling body on the coal pillar, the stability of the coal pillar is effectively guaranteed, which provides a reference for the control of coal pillar deformation under similar conditions.

Caustics experimental study on the interaction between moving cracks and voids under impact loading

Luo Haohao, Zhang Yuantong, Zuo Jinjing, Li Chengxiao, Li Weiyu

2022, 7(2): 210-216. doi: 10.19606/j.cnki.jmst.2022.02.008

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Abstract:
In order to study the fracture characteristics of semi-disc specimens with circular defects under different impact speeds, Hopkinson rod is used to dynamically load the semi-disc specimen, and the fracture process of the semi-disc specimen is observed by the dynamic caustics test system, Through the combination of the two test systems, the fracture characteristics of the semi-disc specimens are studied, the research results show that: before the crack initiation, the focal speckle radius jumps, which is caused by the repeated loading of the incident rod. With the increase of the impact velocity, the peak stress intensity factor of the crack passing through the circular defect increases, and the propagation speed of the crack passing through the circular defect also increases significantly, which shows that the impact velocity contributes to the crack propagation. With the increase of the radius of the circular defect, the stress intensity factor of the second crack initiation at the circular defect becomes larger.

Utility tunnel disaster impact assessment and disaster reduction analysis based on graph theory and AHP

Zhang Zhaoran, Yu Tianfu, Xiang Fangbei, Liu Guoqing, Xia Yuxin

2022, 7(2): 217-224. doi: 10.19606/j.cnki.jmst.2022.02.009

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Abstract:
There are a variety of municipal pipelines in the underground utility tunnel, and once an accident occurs, the property loss and social impact will be huge. Disaster prevention and reduction can be achieved by accurately evaluating the impact value of disasters in the operation stage of utility tunnel and quantitatively analyzing the impact range and degree of disasters. This paper analyzes the evolution process of the internal and external disaster-causing factors and the disaster evolution path in the operation stage, and establishes a disaster evaluation model based on graph theory and AHP method. Taking Tongzhou section A utility tunnel project as the background, the model was used to obtain the impact values of each disaster in the utility tunnel and determine the disaster chain that needs to be managed. The research shows that the major factors affecting the disaster value of Tongzhou section A utility tunnel are explosions, earthquakes, quality problems and design problems. A chain-broken disaster reduction in terms of hazard factors, disaster-pregnant environment and disaster-bearing bodies is proposed. The research results can provide reference for disaster prevention and reduction of utility tunnel.

Research on early warning of mining high voltage cable internal-caused fire based on thermal circuit

Wang Yanwen, Zhang Xuran, Gao Yan, Wang Yinsheng

2022, 7(2): 225-232. doi: 10.19606/j.cnki.jmst.2022.02.010

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Abstract:
The abnormal increase in the temperature of the cable core is an extremely early phenomenon observed during a mining cable internal-caused fire; therefore, the cable internal-caused fire warning system relies on the prompt and accurate measurement of the cable core temperature. The paper proposed a thermal circuit model to calculate the core temperature from the surface temperature of the outer sheath of the cable. The steady-state thermal circuit model is suitable for calculating the temperature when the cable is working normally and the current is stable, whereas the transient thermal circuit model is suitable for calculating the temperature when the cable is faulty. The calculation error of the model is analyzed through the internal-caused fire experiment of the mine cable, and the feasibility of the model algorithm is verified. The results show that the values obtained using the thermal circuit model are in good agreement with the experimental values, and the relative error is less than 10 %, which can be considered to be the criterion for providing early warning in case of a mining cable internal-caused fire.

Corrosion mechanism of ZTAp-Fe material used in coal transportation equipment

Fan Lei, Fan Xingshuai, Zhang Xiancheng, Hu Chun, Ren Qinghai

2022, 7(2): 233-239. doi: 10.19606/j.cnki.jmst.2022.02.011

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Abstract:
Due to the harsh underground environment, underground coal transportation equipment made of traditional steel materials has a relatively low service life. Through electrochemical test, scanning electron microscope observation, energy spectrum analysis and other tests, the law of corrosion resistance, microstructure and element distribution of ZTAp reinforced iron matrix composites prepared by powder metallurgy is explored, the corrosion resistance mechanism of ZTAp-Fe material is revealed. The results show that ZTAp and the iron matrix are in good bonding state in the ZTAp-Fe materials, and the interface is non-metallurgical bonding. With the introduction of 20 % ZTAp in the iron matrix alloy, the corrosion rate decreased from 0.909 28 mm/a to 0.365 14 mm/a, and the resistance of charge transfer (R_ct)increases from 775.6 Ω·cm² to 1025.3 Ω·cm². The corrosion resistance of ZTAp is better than that of iron matrix. The formation of corrosion products at the interface effectively inhibits the corrosive medium from further corroding the interface between ZTAp and the iron matrix. ZTAp reinforced iron matrix composites can effectively increase the service life of coal transportation equipment.

Effect of gypsum on early hydration of amorphous C₁₂A₇ and its mechanism

Tang Guanbao, Wang Dongmin

2022, 7(2): 240-246. doi: 10.19606/j.cnki.jmst.2022.02.012

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Abstract:
In order to promote the efficient application of amorphous C₁₂A₇ in early strength and rapid setting engineering materials, and understand the interaction mechanism between gypsum and amorphous C₁₂A₇, the influence of gypsum on the early hydration of amorphous C₁₂A₇ was studied by X-ray diffraction, scanning electron microscopy and isothermal calorimetry. The results show that proper dosage of gypsum can retard the hydration of amorphous C₁₂A₇, with the increasing dosage of gypsum, the time of the first exothermic peak is retarded, the second exothermic peak of hydration is reduced, and the duration of exothermic peak is prolonged; After 24 hours hydration, the accumulate heat of hydration of the sample with 50 % gypsum are the highest. In the experiment, ettringite and AH₃ gel are the main hydration products. The content of gypsum and hydration ages can change the morphology of ettringite, and affect the compressive strength of the sample. At the same age, with the increase of the dosage of gypsum, the compressive strength of the hydrated pastes increases from 33 % to 50 % and then decreases from 50 % to 64 %. Amorphous C₁₂A₇ with 50 % gypsum system has the highest strength at day 1, day 3 and day 7.

Biodegradation characteristics of phenol and quinoline by Alcaligenes faecalis and its immobilization application

Zhao Qiancheng, Su Kaiwen, Qiu Ziliang, Wang Qingyu, Yu Caihong

2022, 7(2): 247-256. doi: 10.19606/j.cnki.jmst.2022.02.013

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Abstract:
The strains that can only degrade phenol or quinoline are limited in practical application. It is more practical to select the tolerant strains which can degrade the compound pollutants. A phenol-quinoline degrading strain KD1 was isolated from activated sludge in a coke-plant wastewater treatment system. KD1 was identified as Alcaligenes faecalis on the basis of morphological characteristics, physiological and biochemical characteristics and the analysis of its 16S rDNA sequence. The optimal degradation conditions showed that strain KD1 had good pH applicability, and the optimal conditions were as follow: inoculation volume 10 %, rotation rate 150 r/min, culture temperature 30 ℃, initial pH value 7.0 respectively. Nitrogen source can affect the degradation of phenol by strain KD1, while strain KD1 can synergistically degrade phenol and quinoline under co-substrate. The degradation reaction of phenol and quinoline can be described with zero order kinetic equation within 700 mg/L phenol and 400 mg/L respectively. The growth kinetics of Strain KD1 could be described with Haldanes inhibition model, and the inhibition concentrations of it were 293 mg/L and 229 mg/L, respectively. The new immobilized carrier prepared by embedding and adsorption can improve the degradation efficiency of co-substrate pollutants.

Analysis of the problems of smart mine construction based on the layer-level-chain reference model

Tan Zhanglu, Wu Qi

2022, 7(2): 257-266. doi: 10.19606/j.cnki.jmst.2022.02.014

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Abstract:
After the process of coal mine informatization has gone through the two stages of construction of digital mines and perception mines, it is currently moving towards a smart mine featuring thorough perception, deep interconnection and intelligent applications. This article, based on the international development background of "Industry 4.0", in accordance with the guidelines and policies of "Made in China 2025", using the industrialization reference models of Germany, the United States, and Japan as references, and combining the characteristics of the coal industryproposes a reference model for smart mine construction in line with national conditions from the perspective of top-level design. The model clarifies the basic elements and relationships involved in the construction of smart mines from the three dimensions of activity level, organization level, and value chain. Based on the reference model, the existing problems and status quo of smart mines are analysed and the directions that should be focused on in the future construction is pointed out.

2022 Vol. 7, No. 2