矿业科学学报

State of the art review of the risk assessment and early warning methods for fault-slip rockburst

Gao Ansen, Qi Chengzhi, Shan Renliang

2022, 7(6): 643-654. doi: 10.19606/j.cnki.jmst.2022.06.001

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Abstract:
Underground engineering generally needs to pass through a significant number of geological structure areas, which can easily induce fault-slip rockburst, threatening the engineering structure's stability.For revealing the mechanism of disaster causing of fault-slip rockburst, the geological structural conditions, spatiotemporal inoculation characteristics, disturbance triggering mechanism, risk assessment indicators and the early warning methods of fault-slip rockburst was systematically analyzed in this study.The results show that fault-slip rockburst mostly occurs in the geological structure area which containing the weak structural plane or bedding plane, and the hard structural surface controls the rockburst crater boundary.The fault-slip rockburst has typical spatiotemporal precursor characteristics.As a matter of fact, the acoustic emission (microseismic) monitoring parameters have a typical precursor of a "relatively quiet period" in the critical failure stage, and the infrared thermal image temperature will appear the phenomenon of short-term abnormality.The natural defect structure provides geological structure conditions for the occurrence of fault-slip rockburst, roadway tunneling provides a slip space for fault-slip rockburst, and the dynamic stress provides disturbance triggering conditions for triggering fault-slip rockburst.

Improve the quality of "dead band" audio-frequency magnetotelluric impedance data using electric field remote reference

Ma Fangyuan, Wang Hui, Cheng Jiulong, Song Baojia, Dong Yi, Chen Zhi

2022, 7(6): 655-661. doi: 10.19606/j.cnki.jmst.2022.06.002

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Abstract:
Magnetic remote-reference is the most practical noise suppression method in magnetotelluric data processing.In actual audio-frequency magnetotelluric (AMT) sounding observation, usually the "one with three" or "one with four" acquisition method is used, i.e., acquiring magnetic field of only one site and simultaneously acquiring electric field of multiple sites, without magnetic field data for remote-reference processing.The natural electro-magnetic field in the 5~1 kHz "dead band" range of signal strength is weak, resulting in the impedance in this band to have "outlies".In this paper, we found that the impedance estimated by using the local magnetic field and the local electric field as the reference in the "dead band" will be "upward" and "downward" biased respectively, while the electric field as the remote-reference channel can significantly improve the impedance quality in the "dead band".After processing the measured data of different reference distances, it is found that the effect of the electric field remote-reference processing is better than that of the local magnetic field and the local electric field.And the effect is comparable to that of magnetic field remote-reference.This has practical implications for AMT data processing.

Inversion of microtremor recordings dispersion curve based on geological unit

Zhao Hongpeng, He Dengke, Hong Yü

2022, 7(6): 662-669. doi: 10.19606/j.cnki.jmst.2022.06.003

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Abstract:
The urban microtremor exploration technology is a method that detects urban underground structures by using the weak vibration of environment.The surface wave is dominant in the microtremor recordings, and the surface wave dispersion curve can be extracted by further analysis of the fretting signal, and the shear wave velocity can be obtained by inverting the dispersion curve.There is a contradiction among the scale of stratigraphic division, the calculation cost and solution stability.The more stratigraphic division layers, the more unknown parameters in the inversion process.Too much stratigraphic division will increase the computational overhead, aggravate the uncertainty of the equation, and make the inversion results inaccurate.In order to solve this problem, this paper proposes an improved algorithm based on geological unit by drawing on previous studies.When the convergence rate of inversion is low, the two adjacent units with small s-wave velocity difference are combined and the combined stratum participates in inversion.Through the analysis of numerical simulation and measured data, the improved inversion algorithm based on geological unit can reduce the uncertainty of the equation, obtain more stable solutions and reduce the computational overhead.

Numerical simulation on the effect of drilling engineering factors on coal fines output in coalbed methane horizontal wells: a case study of Liulin block

Wei Yingchun, Wang Yadong, Zhang Jin, Wang Anmin, Meng Tao

2022, 7(6): 670-679. doi: 10.19606/j.cnki.jmst.2022.06.004

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Abstract:
The coal fines output is the key factor restricting the development of coalbed methane.Factors affecting coal fines output include static factors and dynamic factors.Drilling engineering is one of the important dynamic factors affecting coal fines output.Taking Liulin coalbed methane block as an example, this study established 2D and 3D models by ANSYS software from the perspective of the wellbore stability, and simulated the force and deformation of the borehole wall under different drilling orientations, drilling fluid density, wellbore size, and wellbore inclination.The influence of factors in drilling engineering on the coal fines production was analyzed for the coalbed methane horizontal well.Results show that borehole size and inclination on coal fines production exert greater effect than borehole orientation and drilling fluid density.When the borehole orientation is along the direction of the maximum horizontal in-situ stress, it demonstrates the biggest difference in the equivalent stress around the borehole, and the most obvious stress concentration.Excessive density drilling fluid will lead to tensile failure of the wellbore.In the process of horizontal well drilling, the larger the radius of the wellbore and the larger the inclination of the well, the easier it is to generate coal fines.In order to reduce the generation of coal fines caused by drilling factors, it is suggested that when drilling horizontal wells in the study area, the borehole orientation should be along the direction of the minimum horizontal in-situ stress, the horizontal section should be drilled with clear water, and the inclination of the horizontal section should be consistent with the inclination of the coal seam.The research results provide a theoretical basis for the control measures of coal fines.

Segmentation of micro-cracks in fractured coal based on convolutional neural network

Zheng Jiangtao, Qi Zihao, Liu Jiacun, Ma Deming, Jü Yang

2022, 7(6): 680-688. doi: 10.19606/j.cnki.jmst.2022.06.005

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Abstract:
The extension, penetration and expansion of coal and rock fracture structure caused by deep mining are the key factors that cause coal and rock damage.Therefore, the accurate characterization of the fracture structure is one of the core elements for understanding the coal and rock failure mechanism and developing coal and gas green co-mining.In this study, the Waifu2x convolutional neural network model was used to process the fractured coal and rock CT images to obtain CT images with higher resolution.And put forward the "seven-step processing method of fissure coal and rock labeling", which improves the efficiency of labeling, and uses image enhancement technology to expand the training set, which meets the model's requirements for the quantity and quality of the training set.The trained U-Net convolutional neural network is used for image segmentation to extract the fracture information in the coal and rock.Through comparison, it is found that the fracture connectivity, opening and distribution obtained by this method are closer to the real CT images, and the four quantitative indicators of the extracted fractures are better than other extraction methods.This study can provide a research foundation for the physical and mechanical behavior and mechanism analysis of fractured coal.

Preliminary investigation on the deformation characteristics of lignite during dehydration process

Song Yanqi, Ma Hongfa, Zheng Junjie, Yang Minjian, Shen Fuxin, Shao Zhixin

2022, 7(6): 689-699. doi: 10.19606/j.cnki.jmst.2022.06.006

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Abstract:
In this paper, the water loss test was carried out to investigate the influence of lignite dehydration on the stability of coal-rock combination slope in open-pit mine.Firstly, the variation laws of water content, deformation, porosity and crack evolution of rock samples were obtained; secondly, the cracking fractal characteristics of sample's end face were analyzed; thirdly, the progressive damage characteristics of dehydrated lignite were studied; finally, based on the principle of capillarity, the law and mechanism of crack propagation for lignite were analyzed.The results show that under the condition of dehydration process, the water loss rate of rock samples presents an increasing trend of "first steep and then slow", and finally approaches or exceeds 10 %.The axial and circumferential deformation increases gradually for lignite samples, and the final strain increases to 0.012 3 and 0.020 3, respectively; meanwhile, the volumetric strain increases to 0.052 8 and has the similar growth trend to the water loss rate.The water loss volume of rock sample is much larger than that of shrinkage volume, and the porosity shows an increasing trend of "steep first and then slow".The lateral cracks of the rock sample develop gradually, and the propagation positions gradually change from upper end to bottom end, and finally to the middle of the rock; meanwhile, the axial cracks initiate and expand.The cracking characteristics of sample's end face are significant, and the fractal dimension of crack distribution shows a linear growth trend, which reveals that there is a transformation process from homogeneity to heterogeneity.The damage variable increases nonlinearly with the water loss rate, and finally increases to 0.066 5;meanwhile, the whole growth process can be divided into linear growth stage, deceleration growth stage, and accelerated growth stage.It is worth noting that the increase of matrix suction controlled by capillary action in the process of pore water loss can be account for the axial and circumferential shrinkage deformation of rock samples, and the initiation and propagation of vertical cracks.

Temperature effect on mode Ⅰ fracture behavior of tight sandstone

Chen Lichao, Lü Shuaifeng, Zhang Diankun

2022, 7(6): 700-709. doi: 10.19606/j.cnki.jmst.2022.06.007

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Abstract:
The fracture complexity of tight sandstone could work to improve the efficiency of tight gas reservoir fracturing.In this paper, three-point bending loading tests was used to characterize the fracture behavior, mechanical properties, fracture path and fracture energy characteristics of tight sandstone at room temperature(RT)and low temperature(LT)of liquid nitrogen(LN₂), and to interpret the pre-fracture mechanism of tight sandstone at LN₂.The results show that: 1)The fracture load and fracture toughness of the tight sandstone treated with LN₂ are significantly lower than those at RT, while the parameters of the samples under parallel bedding slightly increased, which may be related to the enhancement of the bedding plane by LN₂.2)After low temperature treatment with LN₂, the complexity of fracture propagation paths increases, the number of fracture increases, and the fracture bifurcation and convergence occurs.The fracture complexity of sandstone is low at RT, and the effect of LN₂ precracking on the fracture complexity of tight sandstone is significant.3)After LN₂ pre-splitting, the fracture energy of tight sandstone decreases significantly, with a maximum decrease of 46.98 %.4)It is found that the fracture paths of tight sandstone mainly develops along the mineral grain boundary and forms intergranular fracture at RT, and the rock transformation degree is low.However, the complex fracture forms are formed by intergranular fracture, transgranular fracture and intergranular fracture, and the formation of transgranular fracture and complex fracture network are promoted under low temperature.The results of this study suggest that low-temperature during fracturing of tight sandstone reservoir can effectively reduce the fracturing pressure, realize the toughening-brittle transformation of rock and improve fracture complexity.

Temporal and spatial distribution and prevention of dust in mining area based on digital fractal principle

Zhao Hongbao, Liu Shaoqiang, Kang Qinrong, Li Yue, Jiang Dongmei, Wu Tong

2022, 7(6): 710-719. doi: 10.19606/j.cnki.jmst.2022.06.008

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Abstract:
In order to reduce the harm of dust dispersion in open-pit coal mine to the mining environment and the damage of personnel and equipment, this paper carried out the research on dust migration, distribution and treatment in open-pit coal mine by taking Hequ open-pit coal mine as the engineering background.The results show that: ①by means of on-site monitoring, this study analyzes the changes of dust concentration in different areas, and further determines the main dust producing areas of open-pit coal mine; ②The fractal dimension is introduced into the migration and distribution of dust, and the relationship between dust particle size, wind speed and fractal dimension is studied; ③A clean, efficient and low-cost chemical dust inhibitor was developed by studying the ratio of chemical dust inhibitor based on polymer materials.The chemical dust inhibitor has a good capture effect on dust particles and can form a film after spraying to prevent secondary dust.

Research on stability control of roadway intersections with nested variable cross-section in deep mine

Wu Yiyi, Xie Shengrong, Zhang Yü

2022, 7(6): 720-729. doi: 10.19606/j.cnki.jmst.2022.06.009

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Abstract:
In deep mines, it is pretty important to maintain the stability of surrounding rock of development roadway with long service life.However, there are often some problems, such as large deformation and support failure in the deep soft rock environment, because of the close connection of the two intersection points in shaft bottom.This study draws on the surrounding rock control of intersection group of nested variable cross-section roadway in a coal mine as the engineering background.Through field investigation and geological survey, it clarifies the properties of 3.9 m close nested connection structure, variable cross-section and large cross-section, as well as the characteristics of large-scale layer crossing.It also analyzes the reasons for the failure of its original support scheme under the deep rheological surrounding rock.For this reason, the refined numerical modeling is carried out, and results indicate that the stress of the main roadway at the side of the triangular rock pillar has a stress subarea of "reduction-superposition-recovery" along the axial direction.The smaller the intersection angle of the two roadways, the longer the axial distance of the region, and the larger the peak value and range of the abutment pressure.With the increasing of cross-section, the stress concentration range of surrounding rock increases in both horizontal and vertical directions.The plastic zone is overlapped multiple times in the connecting section, and its width is increased more than twice.At the same time, there is an obvious discontinuity in the crossing layer, and the range of the variable cross-section roadway section and the connecting section are rapidly expanded.Therefore, this paper put forward a sectional reinforcement control scheme based on hollow grouting anchor cable, and through on-site observation and monitoring, the reinforcement support effectively ensures the stability of the surrounding rock of the deep well intersection group.

Ma Zhiqi, Yang Xiaobin, Liu Tenghui, Li Zhihui

2022, 7(6): 730-737. doi: 10.19606/j.cnki.jmst.2022.06.010

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In order to study the deformation behavior of sand granular material accumulation during settlement, this study carried out the triaxial compression creep test by step loading, and obtained three groups of creep deformation-time curves of glass beads with different particle sizes (0.6~0.8 mm, 1.0~1.5 mm, 2.0~2.5 mm).The four element Burgers model was selected to fit and analyze the test curve, from which the parameters of creep characterization of glass beads were obtained.The discrete element numerical model was established to verify the parameters of the Burgers model.Results show that the creep characteristics of glass beads under triaxial compression can be described by the Burgers model.The four parameters E_k、E_m、η_k、η_mof the Burgers model have negative correlation with particle size and axial pressure.The macro Burgers model parameters obtained from the test are transformed into the micro Burgers model parameters in the particle flow program.The simulation results are in good agreement with the test results.The comparison results verify that the particle flow Burgers model is suitable for the experimental study of rock particle creep.

Research progress of surfactantaqueous solution inhibiting the desorption of gas in coal

Zhang Xuejie, Chen Mingyi, Zhang Tonghao, Song Zhilei, Zhang Lei, Tian Fuchao

2022, 7(6): 738-751. doi: 10.19606/j.cnki.jmst.2022.06.011

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Abstract:
With the increase of burial depth of coal seam, the gas pressure and gas content of coal seam tend to rise, resulting in the serious problem of gas concentration exceeding the limit.Generally, adding surfactant aqueous solution is an important technical means to reduce coal seam gas emission.In this paper, the application of surfactant aqueous solution in the prevention and control of coal mine gas disaster is analyzed by the literature survey method.The results are as follow: ① based on the consideration of safety and gentleness effects, the descending order of the optimization of surfactants is amphoteric and biological, non-ionic, anionic and cationic, and most non-ionic and amphoteric surfactants have good compound performance.② In the test concentration range, except for biological surfactants, an inflection point for the variations of surface tension and contact angle with solution concentration can be observed for other types of surfactant aqueous solutions, and the corresponding critical micelle concentration (CMC) is 0.1 %.Moreover, the descending order of the wettability effects of these surfactants is anionic, non-ionic, amphoteric, cationic and biological.③ The addition of surfactant aqueous solution can significantly inhibit the desorption-diffusion capacity of gas in coal, which is closely related to the wetting spreading effect and blocking effect of aqueous solution.

Visualization analysis of current research situation in field of deep coal mining

Zeng Jingwei, Jing Guoxun, Zhu Qifeng

2022, 7(6): 752-762. doi: 10.19606/j.cnki.jmst.2022.06.012

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Abstract:
In order to fully understand the current research situation in field of deep coal mining, took the relevant literature of web of science database from 2003 to 2021 as a sample, this paper made an in-depth analysis on the number of papers issued, research institutions, countries, authors, literature citations, keywords and disciplines.The results showed that China's research level is at the forefront of the world in terms of the number of papers issued, research institutions and national levels; Chinese scholars pay high attention to this field in terms of the author; highly cited documents are mostly engineering and technical studies in terms of literature citation; from the perspective of keyword development and evolution, the keywords in this field mainly focus on model, rock, numerical simulation, mechanism and stress, model and numerical simulation will be the important research methods in this field in the future.From the perspective of discipline development and evolution, disciplines in this field mainly focus on engineering, geology, multidisciplinary geoscience, energy and fuel, environmental science and ecology, sustainable development will become the hot research directions in the future.

On stability and synergistic effect of nano-bubbles in micro-silica flotation

Li Jun, Sun Jianxiang, Xu Zesheng, Li Xiaodong, Zhao Jiajia, Liu Jia

2022, 7(6): 763-769. doi: 10.19606/j.cnki.jmst.2022.06.013

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In order to solve the purification problem of microsilica powder and improve the flotation recovery, this study introduced nano-bubbles into the flotation of micro-silicon powder, and analyzed the effect of nano-bubbles on flotation purification of microsilica powder.Nanoparticle Tracking Analysis (NTA) was used to determine the stability of nano-bubbles and the effect of sodium oleate on their stability.Results show that with the same amount of collector, the recovery of SiO₂ can be improved by introducing nano-bubbles into the flotation of micro-silica powder; When the amount of collector was 1.5 g/L, the recovery of SiO₂ reached the maximum of 70.2 %; Sodium oleate can improve the stability and dispersion of nano-bubbles in water; Nanobubbles can improve flotation recovery since there is a synergistic effect between nano bubbles and ordinary flotation bubbles produced in flotation.

Migration and enrichment of arsenic during coal washing

Xie Weiwei, Zhou Lingmei, Zheng Hao

2022, 7(6): 770-781. doi: 10.19606/j.cnki.jmst.2022.06.014

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During the processing and utilization of coal resources, some heavy metal elements will be enriched in the environment, which is harmful to the environment and the human body.In this study, low-ash, high-sulfur coal samples and high-ash, low-sulfur coal samples from Inner Mongolia were selected for float-and-sink test and flotation, and were analyzed by inductively coupled plasma mass spectrometer (ICP-MS), X-ray diffraction analysis, X-ray fluorescence analysis, and scanning electron microscopy energy spectrum analysis.Infrared spectroscopy and other test methods were used to study the occurrence form of heavy metal arsenic in coal and its migration and enrichment law during the processing.The experimental results show that the two coal samples demonstrates the highest proportion of arsenic present in the aluminosilicate bound state, reaching more than 50 %, but the types of aluminosilicate minerals are not the same, and the occurrence of arsenic has obvious differences.Flotation results show that arsenic in low-ash and high-sulfur coal sample is mainly associated with minerals and concentrated in the denser part, while high-ash and low-sulfur coal is mainly concentrated in the part with lower density and higher organic content; there are also differences in the migration law of arsenic in flotation.During the flotation, the arsenic in low-ash and high-sulfur coal migrates to the tailings, while the arsenic in the high-ash and low-sulfur coal migrates to the clean coal.The above findings show that it is feasible to remove arsenic from low-ash and high-sulfur coal sample by flotation but the effect is not so good for high-ash and low-sulfur coal sample, indicating that the removal of arsenic must consider the impact of coal type.

Optimization of fluorine mine water treatment and fluorine removal mechanism using response surface methodology

Zhang Liping, An Yiyun, Wu Eryong, Yao Ruihan, Zhao Xiaoxi, Yuan Hexia, Yang Yixuan, Song Jingxi

2022, 7(6): 782-792. doi: 10.19606/j.cnki.jmst.2022.06.015

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Abstract:
Surface water or groundwater flowing through fluorine-rich rocks can easily lead to excessive fluorine in water.Excessive fluoride in water can cause endemic fluorosis, damage of the ecological environment and restrict comprehensive utilization of water resources.In this study, based on a highly effective fluoride removal agent developed by the research group earlier, the box-Behnken method of response surface analysis was applied to design fluoride removal experiments where the influences of pH value, dosage of defluoridation reagent and fast stirring time on fluoride removal effect were optimized.This paper used X-Photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Fourier transform infrared spectrum (FT-IR) to characterize the defluoridation reagent and the sludge produced after treatment, and discussed the mechanism of fluoride ion removal.The experimental results showed that F^-could be reduced from the initial 20 mg/L to 0.453 mg /L under the optimal conditions of fluoride removal (pH value 6.11, dosage 4.15 mL, fast stirring time 10.90 min), which was basically consistent with the predicted value 0.445 mg /L of the model.The defluoridation reagent was mainly through the formation of Fe, Al, Si and O polynuclear polyhydroxyl complex, fluorine-ion exchange with hydroxyl and replace hydroxyl, then fluorine-ion was fixed in the polynuclear polyhydroxyl complex.Meanwhile, fluoride forms a tetrahedral structure of aluminum, silicon and oxygen, and locks fluorine ions in the tetrahedral structure to achieve fluoride removal.Compared with the current main treatment process using hydroxyapatite adsorption, the defluoridation reagent in this study has the advantages of simple treatment process, stable treatment effect and low treatment cost.

2022 Vol. 7, No. 6