Search

Data governance capability is fundamental to coal mine intelligence construction. It could accelerate the intelligent construction of coal mines and promote the digital transformation of the coal industry so as to building a modern energy system in digital China. This paper therefore discusses the theory and methods of improving data governance capability for intelligent coal mines. Specifically, this study analyzes its strategic demands of intelligent coal mine construction on data governance and offers a working definition for data governance capability for intelligent coal mines. Then an evaluative system is proposed for the evaluation of data governance capability for intelligent coal mines. Further, by drawing on capability maturity theory, this study establishes a maturity model that specifies the improvement path of data governance capability for intelligent coal mines. Finally, based on the PDCA cycle theory, this paper puts forward strategies for improving data governance capability for intelligent coal mines, in order to 1)supplement existing theories of data governance capability enhancement, and 2)provide references for future practices of data governance.

The fully mechanized mining face adopting pre-driven recovery room is prone to large roof deformation at the final mining stage, which will lead to support crushing accidents. Based on the three main roof failure forms after longwall face entered recovery room, this paper established different mechanical models for roof sag of the recovery room. By analyzing energy release and work process in roof deformation, this paper obtained the immediate roof sag of recovery room under different main roof failure forms. Taking the large roof deformation and support crushing accident of recovery room in the N14201 longwall face of Zhangjiamao Coal Mine as example for analysis, this paper analyzed the influencing factors of the models and found that the main roof break position, the thickness of key block and its overlying strata, the rotation angle of key block and the supporting intensity have significant impact on the roof sag of recovery room. The research results confirmed that the reason for the support crushing accident in N14201 longwall face of Zhangjiamao Coal Mine: the main roof is broken within 4~6 m above the protective coal pillar, and the main key stratum is broken and unstable due to the mining of upper 3-1 coal seam.

High-voltage electric pulse(HVEP)drilling has become a new and efficient rock breaking method, which is also the research focus in the field of drilling speed increase. To probe into rock breaking mechanism of high voltage electric pulse, this study establishes a two-dimensional numerical model of multi-physical field coupling electric breakdown of single pair of electrodes. The model reproduces the generation of plasma channels in homogeneous red sandstone from the coupling of current field, electric breakdown field and circuit field. This paper analyzes the effect of electrode pair angle, voltage and electrode spacing on rock electrical breakdown(that is, the formation of plasma channel in rock). The model includes the circuit structure parameters of pulse tool, the occurrence and development of electrical breakdown, and the relationship between electrical breakdown intensity and time. Results indicate that the plasma channel begins to sprout from the partial area near the top of the discharge electrode and develops towards the partial weak dielectric strength. With the voltage value of loading pulse increasing gradually, the time of electrical breakdown decreases gradually; comparatively, the equivalent failure volume of rock model increases gradually, and there is a positive correlation between them. On the precondition that the rock can be electrically broken, increasing the electrode spacing can improve the rock breaking efficiency of high voltage electric pulse. The equivalent failure volume of rock shows significant fluctuations during the gradual increase of electrode inclination angle of discharge electrode, and its extreme value mostly appears in the range of electrode inclination angle of 35°~ 55°. To further promote the industrial application of high-voltage electric pulse rock breaking, this paper proposes a three-dimensional numerical model of multi-physical field coupling dynamic electric breakdown of red sandstone based on two-dimensional model, reproducing the appearance of the fracture crater in the rock during the rock breaking process with electrode bit. At the same time, the self-designed coaxial electrode bit is selected for experiments of electric breakdown, and the laboratory experimental results of electric breakdown confirm the simulation experimental results.

Coal seam mining causes deformation, fracture and migration of overlying rock, further leading to the surface subsidence and ecological damage, which are the main manifestations of mining damage.Quantitatively characterize mining damage is the key to analyzing the stability of surrounding rock, designing mining parameters, and the premising of roadway support parameters.According to the finite element and discrete element simulation methods commonly used at this stage, this paper proposes a quantitative index(damage degree)to characterize mining damage: the proportion of zone plastic volume and the proportion of contact fracture length(number).On this basis, this study carried out the optimization of high-intensity mining parameters of the western mining area, the stability analysis of the coal pillar under the condition of mining and water immersion, and the progressive damage characteristics analysis of the roadway surrounding rock in the water-filled fault structure area by using the damage degree index.The quantitative relationship between the damage degree of the overlying rock and the mining parameters is obtained, which can realize the reasonable optimization of the mining parameters.This paper revealed the progressive damage characteristics of mining water immersion in coal pillars.We deemed that there is a danger of water seepage in the mined-out area as a water storage area under the existing coal pillar conditions.This study quantified the damage distribution characteristics of the surrounding rock in the roadway in the water-filled fault structure area, and proposed the corresponding? solution of dredging the fault through the roof aquifer, grouting reinforcement of the original fault fracture and strengthening the support.By comparing with common indicators such as the height of the water-conducting fracture zone and the width of the plastic development of the coal pillar, this research found that the damage degree indicators are more sensitive to the characterization of mining damage, and could realize continuous mining damage characterization.

The study of the transient electromagnetic detection device with small sized coil and easy installation underground will offer new insights into the real-time dynamic exploration and forecast water-bearing structure in excavation roadway.By drawing on the full-space transient electromagnetic theory, this paper adopted the three-dimensional time-domain finite element method for numerical simulation to explore the characteristics of the secondary field response obtained by small coil excitation and the transient electromagnetic response received by the magnetic core coil.This study constructed a geological-geophysical model of the water-bearing fault in front of the roadway excavation working face, studied the transient electromagnetic response characteristics of the small coil device for the water-bearing fault, and compared the effects of small coil and conventional coil in advance detection.The study shows that : ①the decay law of the induced electric potential generated by the small coil source excitation is the same as that of the induced electric potential generated by the conventional transmitting coil with time, ②the magnetic core coil can effectively improve the induced signal strength, ③the application of both the small coil device and the conventional coil device can effectively explain the distribution range of the low resistance area, ④the detection results match the verification results of the roadway excavation.Combined with the underground field test, this paper verified the applicability and effectiveness of the small coil device applied to mine transient electromagnetic method advance detection.

This paper proposed a new method for the determination of chlorine in coal by Eschka's mixture decomposition-ion chromatography so as to satisfy the needs of determining chlorine content in coal samples in large batches in coal exploration, coal production and processing industries.Specifically, this paper improved the sample pretreatment steps and determined the experimental parameters.The detection limit of the method was 0.001 7 %, the relative standard deviations of ten parallel determinations of three actual coal samples were in the range of 1.08 % ~3.92 %, the recoveries of six spiked determinations were in the range of 98 % ~104 %, and the results of the three standard coal samples were all within the guaranteed values.Results showed that the detection limit of the method was lower than that of the national standard method, and the precision and accuracy met or exceeded the national standard method.The determination of chlorine in coal by Eschka's mixture decomposition-ion chromatography has the advantages of simple operation, low cost and high determination efficiency and could be widely applied in the batch determination of a large number of samples.

In order to reduce the occurrence of safety production accidents in coal mine industry, this paper combined the definition of safety behavior and unsafe behavior, behavior safety theory and MMEM system theory to put forward the standard definition of safety state of coal mine workers' behavior.According to the behavior influencing factors, this study established the coal mine workers behavior safety state evaluation index system, including 4 first-level indicators 21 secondary indexes.The Improved-AHP method, Entropy Weight method and variance coefficient method were adopted to determine the subjective and objective weights and weight combination.Taking one mine as example for analysis, this paper chose extension comprehensive evaluation method to construct the evaluation model. Results show that: For the coal mine industry, the defined-evaluation-improvement(D-E-I)model is universal.The empirical evaluation level is Ⅳ or "relatively safe".The evaluation results are in line with reality, and the model is scientific and practical.

The purification effect of coal mine groundwater reservoir on mine water mainly lies in the water-rock coupling between the rock mass and mine water.This paper systematically reviews the research methods of water-rock coupling in coal mine underground reservoirs, and presents the characterization methods of water quality and physicochemical properties of rock samples.It employs static simulation, dynamic leaching, cycle purification simulation and other tests to explore the purification regulation of mine water in coal mine underground reservoir, uses numerical simulation to obtain the selective adsorption trend of ions in the reaction process, and combines Piper three-line diagram, Gibbs model and correlation analysis to reveal the mechanism of water-rock coupling.The purification effect and research progress of suspended solids, specific ions and organic matter in coal mine underground reservoirs are discussed.The paper shows that underground reservoir of coal mine has a certain purification effect on mine water, and the purification effect of specific ions is mainly related to filtration and adsorption.Three research directions of coal mine underground reservoir purification technology in the future are proposed: ①developing large-scale and low-cost treatment technologies for underground mine water based on water-rock coupling purification, ②developing a "three-in-one" water quality control technology for coal mine underground reservoirs coupled with multiple water treatment technologies, and ③exploring the underground storage and resource utilization technology of concentrated salt wastewater for the future studies of water-rock coupling.

The problem of overlapping mineral rights of coal and gas is common in the Ordos Basin of China.The interaction will occur when coal and gas are mined simultaneously, so it is necessary to solve the synergistic mining problem to eliminate the accident potential.Considering that there are many constraints in the simultaneous exploitation of gas and coal, this paper proposed an energy control failure model by energy abnormal release and STAMP.This model explains the applicability of information transfer cycle and the energy control failure model.Then, through the analysis of gas-coal mining process, this paper established the interaction between the energy unit, barrier unit, and disaster-bearing body, and analyzed the characteristics of energy transfer and safety barrier interaction.Finally, by analyzing 9 kinds of accidental release scenarios, this study proposed the identification behavior methods and control measures to prevent gas-coal cross-mining accidents.

Faults are an important factor inducing mine safety accidents, and it poses difficulties on the identification of faults within 5 m of drop.Taking the Liupanshui coalfield of Guizhou province as the study area, this paper investigated the coalfield strata and carried out an on-site survey.It proposed a seismic physical model and used the unique velocity ratio of 1∶1.74 to realize the construction and analysis of small faults with a burial depth of 800 m, 1 000 m and 1 200 m and a drop of 5 m, 3 m and 1 m.This paper extracted a variety of seismic properties by seismic dynamics method to analyze small faults, and obtained the sensitivity of seven seismic properties to the characteristic response of small faults, including amplitude envelope, amplitude first derivative, and amplitude second derivative, and the correlation between seismic properties and drop was established accordingly.The results show that when the small fault drop of the coal seam is less than or equal to 5 m, there is a linear relationship with the traditional amplitude attributes, and a linear relationship with the seismic properties related to phase and frequency.There is high correlation between the amplitude envelope and the amplitude imaginary part, and low correlation between the instantaneous frequency, the amplitude first derivative, the cosine instantaneous phase, the amplitude second derivative and the amplitude envelope.

Based on a large number of field investigations and the analysis of the "analogous hyperbolic" overall movement model proposed by the author, this paper further extends it to three-dimensional space, and proposes a full-space "analogous hyperboloid"three-dimensional movement model of the mining strata.There are two types of hyperboloids, "quasi-single-leaf"and "quasi-double-leaf", which can approximately describe the three-dimensional movement and surface subsidence characteristics of full-space mining strata under different lithological conditions.The "analogous single leaf hyperboloid" model is a horizontal moving boundary model of the spatial rock layer, which is implicit in the thick loose layer overlying rock; the "analogous double leaf hyperboloid" model is the vertical movement of the spatial surface subsidence and the overlying fissure arch and caving arch.The boundary models are approximately symmetrical with the "origin" in the main key layer, and are embodied in external forms such as surface subsidence under mining disturbance and arch caving of the surrounding rock in the stope. Through theoretical analysis, similar model test and 3DEC numerical simulation, this paper deduces and proves in detail the "analogous hyperboloid" model of spatially mined rock strata movement and surface subsidence under the condition of near-horizontal coal seam mining in thick loose layers.At the same time, this study analyzed the composition conditions, influencing factors and overall migration law of the co-asymptotic conical surface "analogous hyperboloid" model.Results show that under the condition of near-horizontal coal seam mining with thin bedrock and thick loose layer, the "quasi-hyperboloid" theoretical model is in good alignment with the 3DEC simulation results, indicating that the overlying rock migration and surface subsidence in space mining are "analogous hyperboloid" feature.

If the shearer is cutting coal using the "memory cutting" technique, a manual demonstration is required.The memory cutting technology has higher requirements on the reserving conditions of coal seams.When the coal seam fluctuates greatly, frequent manual demonstrations are required.The "memory cutting" technology only optimizes the cutting path of the coal seam roof for the next cutting.Along the advancing direction of the shearer, it is impossible to accurately plan and control the pitching angle of the shearer according to the reserving conditions of the coal seam.Based on the concept of shearer self-adaptive intelligent cutting, this paper designs the operation mode of the shearer intelligent cutting system in the fully mechanized working face.In this model, the high-precision three-dimensional geological model of the working face is first constructed by using the highly accurate geophysical data of the coal seam, and then the future cutting path of the shearer is planned by using the model.At the same time, the high-precision three-dimensional geological model is dynamically corrected by using the latest geological data of the working face during the mining process.In this paper, the high-precision three-dimensional dynamic geological model is coupled with the shearer mining planning algorithm.According to the model, a shearer mining control baseline planning algorithm that can adapt to the changes of the coal seam is proposed, which realizes the pitching control of the shearer in the advancing direction and the cutting control in the pulling direction, as well as the efficient cooperation between the update of the geological model, the planning of the mining baseline and the adjustment of the shearer drum.The calculation service interface of the drum adjustment parameters in the intelligent cutting system and the communication protocol between the intelligent cutting system is designed.Addtionally, the shearer control system is considered.This realizes the precise control of the shearer drum based on the planning cutting path.The intelligent cutting system of fully mechanized working face is applied to guide the production of shearers.The practice shows that the shearer intelligent cutting system is suitable for coal seams with various degrees of floor inclination.The cutting line of the shearer can better fit the roof and floor lines of the coal seam, which can save resources and improve production efficiency.

In order to find out the key causes of changes in spontaneous combustion characteristics of igneous intrusive coal seams, this paper took the Daxing Coal Mine in Tiefa Coalfield as example for analysis, which was widely invaded by igneous and had serious coal spontaneous combustion disasters.Metamorphic coal and unaffected primary coal were collected from the study area.Specifically, this paper studied the patterns of heat production and temperature rise, gas production rules, and microscopic structure parameters of coal samples by synchronous thermal analyzer and coal spontaneous combustion characteristic measuring device.The experimental results show that the igneous intrusion caused the mutation in the spontaneous combustion characteristics of the coal.Compared with the primary coal, there was significantly higher oxidation heat release of the metamorphic coal at the low temperature stage.Also, the crossing point temperature of metamorphic coal was reduced by 13.2 ℃, and it entered the stage of oxidation and weight gain earlier than the primary coal.When the environment temperature exceeded 90 ℃, the oxidation heat generation and reaction rate of metamorphic coal increased rapidly, which showed higher oxygen consumption rate and faster generation rate of oxidative gas products such as CO and CO2.This demonstrated higher oxidation activity of metamorphic coal than that of primary coal.The analytic results of physicochemical microstructure showed that the high temperature and pressure of igneous intrusion changed the pore structure of coal, which reduced the pore volume and specific surface area of micropores/mesopores in metamorphic coal, and the pore volume of macropores was three times higher than that of primary coal.The average pore size and porosity increased significantly, which was conducive to the transport, migration and adsorption reaction of oxygen molecules in the coal structure.At the same time, igneous intrusion reduced the oxygen-containing functional groups of metamorphic coal, and the content of aliphatic hydrocarbons with higher activity increased from 27.98 % to 29.07 %, which enhanced the oxidative activity of metamorphic coal.Moreover, igneous intrusion caused problems such as increased air leakage, long oxidation time of left coal, and wide oxidation zone during the mining, eventually leading to severe coal spontaneous combustion disasters.

With the increase of coal mining depth, the stress environment of the surrounding rock of the roadway deteriorates, therefore it becomes a prominent problem for the large deformation of the surrounding rock and the breaking of the bolt and cable, which seriously affects the safety of deep mine production.To solve such problems, this paper focuses on the advantages and disadvantages of bolt and cable support.Based on the interaction mechanism between Anchor Cable with C-shaped tube(ACC)and surrounding rock, this paper proposed a new ACC support technology.ACC optimizes the stress state by improving the structure of the free section of the anchor cable.It can not only enhance the anchor cable's axial bearing capacity but also prevent the free section of the anchor cable from breaking due to lateral action.It can avoid the problem of instability of surrounding rock.Through the shear test, it is found that the maximum shear load of the ACC is more than 1.27 times that of the ordinary anchor cable, and the average maximum shear displacement is 1.16 times that of the ordinary anchor cable, which indicates that the ACC has good shear resistance and shear direction extension properties.Based on the engineering case of the roadway of Jiulong Mine, this study analyzes the deformation and failure characteristics of the roadway under the original support scheme through on-site monitoring and borehole detection, and has successfully applied the ACC in the deep large-deformation roadway.The field monitoring results show that the new technology of ACC can effectively control the large deformation of surrounding rock.The results of this study can provide reference for similar deep mine support.

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.

In view of the problems posed by low pozzolanic activity and large water requirement of normal consistency in the direct light calcinating of electronic fluorine-containing sludge as cement admixture, this paper uses coal gangue as a supplementary silicon and aluminum source of electronic fluorine-containing sludge to mix electronic fluorine-containing sludge and coal gangue and then to prepare cement admixture by light calcinating. This paper studied the effect of cement admixture prepared by light calcinating electronic fluorine-containing mixed with sludge coal gangue on cement properties through strength activity index, mechanical properties of cement, water requirement of normal consistency, setting time, particle size, X-ray diffraction and scanning electron microscopy. The results show that compared with direct light calcinating of electronic fluorine-containing sludge to prepare cement admixture, light calcinating of electronic fluorine-containing sludge mixed with coal gangue can improve the particle gradation of cement and reduce the water requirement of normal consistency of cement. It can significantly improve the activity of cement admixture and the strength of ordinary portland cement. Significantly extending the initial setting time and shorten the final setting time of cement.

Due to the exploitation of mineral resources in the deep underground space, it is more and more important to study the variation trend of deep in-situ stress field. In recent years the researches have updated many in-situ stress data. It is necessary to improve the existing estimation methods on this account. Based on the basic theory of elasticity and spherical shell model, this paper studied the effect of gravitational body force varying with depth and internal pressure, and obtained the theoretical formula of macro in-situ stress distribution; Employing the latest and widely distributed measured data, this paper fitted the crustal physical parameters in the theoretical formula, and obtained the fitting formula of vertical in-situ stress and average horizontal in-situ stress varying with depth. The results show that: the distribution of crustal stresses with depth is no longer linear on the macroscopic scale of the Earth; however, within the current depth range of human activities, basically the average in-situ stresses vary linearly with depth, which is closest to the results of the Dinnick hypothesis at γ=22 kN/m3 and λ=0.9; with the increase of depth, the average lateral pressure coefficient gradually approaches 1, which is closer to the measured data than the envelope proposed by Brown and Hoek; the high pressure in the crust will cause horizontal tensile stress, but the compressive stress generated by gravity is higher and therefore the vertical and horizontal in-situ stress in the whole crust are compressive stress. The research results provide a theoretical prediction model for the estimation of crustal stress distribution trend, especially in deep underground space.

Based on the fracture mechanics theory of the isotropic Hoek-Brown strength criterion, this paper established the initiation conditions of the bifurcated microcrack along bedding which begins with the meso-fracture mechanism of laminated rocks. Then the author substituted the critical angle which indicates that the initial crack most likely causes the fracture of the rock into above established conditions and derived the anisotropy expression of the parameter m1 for the weak plane of bedding leading to the crack deflection. Through introducing the correction coefficient for the mixed fracture of the rock along the bedding and the matrix, this paper obtained the anisotropic modified model of Hoek-Brown strength criterion. Compared with the established anisotropic Hoek-Brown model and shale triaxial test results, the validity of the model was proved. The modified model inherits the fracture mechanics analysis of the isotropic Hoek-Brown strength criterion for the selection of rock failure characteristic quantity, and reflects the microscopic failure mechanism of the rock, also considers the effect of bedding anisotropy. The parameters in the modified criterion have a clear physical meaning. The parameter m in the model is related to the angle of the bedding plane, the tensile strength, compressive strength and friction coefficient of bedding and matrix. The change in the friction coefficient of the bedding plane will cause the position of the minimum value of m and the rock strength characteristics changed.

Rock heterogeneity (such as mineral inclusions, micro-cracks, micro-voids and other microstructures) significantly affects its nonlinear mechanical behavior and failure process. This paper utilizes the Fast Fourier transform-based(FFT) numerical method which does not require meshing of complex microstructure but directly obtains the microstructure of heterogeneous materials through the pixels of the image. In addition, the method can be naturally combined with digital image processing (DIP). An actual-microstructure-based FFT method is thereby developed to simulate the elastoplastic behavior of the heterogeneous rocks under external load. The influence of microstructure on the nonlinear behavior is discussed as well as the internal relationship between the microstructure and the macroscopic mechanical properties. The results show that the real-microstructure-based FFT method can well predict the nonlinear behavior before and after the peak strength of the rocks under different depths and confining pressures. The shape, size and distribution of microstructure directly determine the distribution of stress field in clay rock. The actual-microstructure-based FFT method proposed in this paper can reasonably consider the rock heterogeneity, and provides an important tool for studying the influence of the rock microstructure characteristics on the nonlinear mechanical behavior.

In order to obtain the fracture development characteristics of the working face with extra-large mining height under the condition of thick overburden and medium mining depth in mining areas in China's western regions, this paper adopted a comparative study by combining empirical equations, numerical simulation and field measurement in the panel 12401 of the Shangwan coal mine.The results show that the empirical equations drawn from data from the typical geological conditions of mining areas in eastern and western China are difficult to apply to this panel with extra-large mining height, thick overburden and medium buried depth.The prediction values of the empirical equations based on data from the geological condition in the western mining regions are generally higher, which are significantly smaller in the eastern mining regions.The value predicted by the numerical simulation based on the damage constitutive model is closer to the measured value than those derived from using empirical equations, with a relative error of less than 5 %.The paper obtained the characteristics of the water-conducting fracture zone development: due to the existence of soft and hard rock in the overburden, the water-conducting fracture zone develops upward as a step, and the shape changes from "arch"(three-dimensional "shell") to "saddle"(three-dimensional "basin shape") with the variation of mining degree.

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.

The subsidence prediction method is very important for predicting the negative impact induced by coal mining.Probability integral method is an important method for mining subsidence prediction, but for irregular working face mining, its prediction accuracy needs to be improved.Aiming at this problem, the Green formula was used in this paper to transform the formula of the probability integration method, and convert the integration of the working face to the line integration of the boundary of the mining area; the boundary of working face was simplified and divided into multiple straight line segments, and each straight line segment was integrated separately; the prediction of the movement and deformation of any point on the surface and the surface subsidence basin was completed through superposition calculation; finally, an application study was carried out based on a certain example, which verified effectiveness of the method in this paper.Compared with the result of the probability integration method, the prediction accuracy of the line integral proposed in this paper was improved by 23 %.

When shield machine is driving for a long distance, it is often forced to stop due to obstacles or excessive wear of tools, which is one of the main risks of shield construction. In order to summarize the research progress of shield opening technology in urban metro, the paper systematically summarizes the two technical ideas of normal pressure opening and pressurized opening, and summarizes the principle, risk factors and principles of shield opening under two technical conditions. Combined with typical engineering examples, the application scope, key technology, advantages and disadvantages of conventional compressed air and saturated gas method with pressure opening technology are analyzed and summarized. The engineering application of atmospheric pressure opening technology and atmospheric pressure cutter disc tool changing technology for soil grouting and freezing reinforcement is summarized. Finally, combined with the current research progress and the development trend of large diameter underwater shield in China, the paper analyzes the technical challenges faced by the shield opening in the future, discusses the direction of further research, and provides a reference for the development of shield opening technology in China.

Knowledge graph is an indispensable part of cognitive intelligence research.Aiming at the problem that the traditional analysis method of stope mine pressure hazard events has insufficient expression of the stress time and space evolution process and the relationship between hazard evolution and risk prevention and control in the coal mining process, this paper proposes a knowledge graph representation method that based on the entire life cycle of stope for mining pressure hazard events.Firstly, from the perspective of geological disasters, the dynamic characteristics of stress and distribution in stope were analyzed.The dynamic correlation of various nodes in mine pressure geological disasters was established, and a knowledge graph representation method for mine pressure geological disasters considering spatiotemporal processes was proposed.Secondly, from the perspective of accidents, the evolution of hazard and the process of risk prevention and control in mine pressure accidents were analyzed.The evolution of hazard and preventive measures were integrated into the knowledge graph representation model.Finally, Neo4j was used to build the knowledge graph of mine pressure hazard events.The results indicate that the knowledge graph constructed based on this representation method not only depicts the spatiotemporal evolution processes of different objects in disaster events but also describes the coupling evolution process of hazards and corresponding risk prevention and control measures.This provides an intelligent research pathway for the prevention and control of mining pressure hazards in intelligent mining.

Using aeolian sand(AS)for backfilling can realize local material extraction and turn waste into treasurethe, and realize coordination of green mining and AS control.The AS filling mining is mainly applied to the backfilling of goaf under Highway, backfilling mining of coal mine and metal mine.Grouting and sand injection in the goaf, solid backfilling mining, high water backfilling mining and cemented backfilling mining are developed.Long wall backfilling mining, strip backfilling mining and roadway backfilling mining are adopted.The research on the properties of cemented AS backfilling materials focused on slurry fluidity and backfill strength.In this paper, the rheological properties of cemented AS slurry with different proportions and curing times are analyzed, and cemented AS backfills are toughened by using polypropylene fiber.The results showed that the rheological parameters of cemented AS slurry increased with the curing time, and the addition of fiber significantly improved the brittleness characteristics of cemented AS backfills.

Mine filling and tunnel spraying projects pose high requirements on the rheological properties of cement-based materials.The types, conditions of fine sands and the exposed environment have significant effects on the rheological properties.In this light, this paper uses coal gangue sand instead of quartz sand as the fine aggregate of cement-based material and investigates the effect of temperature and aggregate prewetting on the rheological properties of mortar and its mechanism.Results show that the shear stress-shear rate relationship of coal gangue mortar conforms to the characteristics of Herschel-Bulkley(H-B)model, with higher rheological index(higher than 1)and higher consistency than that of quartz sand mortar.The apparent viscosity of coal gangue mortar decreases with increasing temperature, but the effect of aggregate prewetting is not significant.The yield stress of coal gangue mortar at 30 ℃ is 2.99 Pa, 1.45 times higher than that at 10 ℃, and 2.13 times higher after prewetting.The thixotropic ring area of coal gangue mortar is higher than that of quartz sand mortar, and the thixotropic ring area of pre-wetting coal gangue mortar is 398.4 Pa/s, while that of dry coal gangue mortar is 283.3 Pa/s.The obtained results are expected to provide evidence for the rational utilization of coal gangue sand and the design and preparation of rheological materials served in complex environment.

China's intelligent mine construction is still in the early stage of development, which is seriously constrained by data trust problems such as low credibility of mine data, lack of trust mechanism in the data sharing process and the risk of data security and privacy leakage.To this end, this paper proposes an intelligent mine data trust model by drawing on the holistic approach to national security.Specifically, this study 1) offered a working definition of this model and proposed its underlying conceptions; 2) designed its technical architecture and analyzed the core technologies involved; 3) proposed the implementation strategies of the intelligent mine data trust model based on blockchain technology.This may lay the foundation for blockchain technology to empower intelligent mines and comprehensively enhance its efficiency and productivity, thus promoting the high-quality development of the coal industry.

This paper, taking the Chinese and English literature of mine safety and digital mine safety management from 1999 to 2019 as the research object, using Citespace visualization software as the research tool, systematically sorted out and analyzed the highly cited literature from the number of documents, research topics, major scholars and research institutions, keywords and keyword centrality. The results show that: papers on mine safety from the perspective of digital mines account for about 20 % of the research papers in the field of mine safety, and show an upward trend year by year, indicating that the related research of digital mines in the field of safety management has always been a hot spot in this field; Most cited Chinese documents are theoretical methods or management studies, while highly cited foreign documents are mostly engineering and technical studies, indicating that there are certain differences between Chinese and foreign academic journals. 61.9 % of the authors of foreign literature are from China, which shows that Chinese scholars have made a great contribution to the research in this field. It also shows that Chinese scholars have taken theoretical method research, management research, and engineering technology research into account at the same time. Current research at home and abroad has a high degree of concentration, strong research intensity, and strong forward-looking nature. It has basically realized the combination of emerging technologies and the safety management of digital mines, which provides the necessary theoretical support for the application and development of digital mines in mine safety management.

In order to prevent major acid drainage pollution accidents, this study aims to improve the accuracy of acid production potential evaluation of mine rocks in the prediction of acid drainage. Specifically, this paper introduced existing calculation methods of acid-producing potential, and then determined the acid-producing mineral contents in some sulfur minerals and coal gangue samples by three-step sequential extraction method, which is then compared with the traditional method of calculating the maximum acid-producing potential by measuring total sulfur. Results show that: 1) the acid-producing potential of coal gangue is dependent on the mass percentage content of each acid-producing sulfur and the corresponding unit acid value; 2) except for sample SC, the acid-producing potential calculated by acid-producing sulfur content is lower than(with different degrees) the acid-producing potential predicted by total sulfur. The sulfur in the sample SC is mainly arsenopyrite sulfur, which has a higher acid value per unit than pyrite sulfur, resulting in a higher acid potential calculated by SC sample than predicted by total sulfur; 3) the three-step sequential extraction is suitable for samples with iron and copper sulfides as the main sulfur minerals; 4) when other sulfide components increase and blank samples are unevenly mixed, the results will be disturbed to some extent. This research provides evidences to justify the evaluation of accurate acid production potential of coal gangue in mining area.

The highly-efficient treatment of coal mine water with low energy consumption contributes to much safer and more efficient coal mining. At present, mine water processing at underground is still limited for its small treatment water yield, large land coverage and high operation cost in ground treatment, high drainage costs when mine water is discharged into the surface water system. In this light, this study puts forward the "deep ground-underground-surface ground" linkage system for mine water treatment and utilization. The treated mine water is partially used for mining production and residential usage, while the rest is subject to deep reinjection or drainage. This paper first introduces the operational mechanism behind this system, and then evaluates its validity in terms of water quality, water quantity, hydrogeology, underground structure, and feasibility of recharge engineering. This study then reviews existing mine water treatment methods for varying water qualities and the "underground-surface" joint treatment system; Also, a summary is drawn regarding the selection of aquifer for reinjection purposes, reinjection construction operations, reinjection tests, simulation of reinjection water quality, and analysis of reinjection safety.

This study attempts to enhance the separation efficiency of dense media cyclone for raw coal feed with difficult-to-cleaning and large high-density component content. Specifically, this paper 1) designed a novel heavy media cyclone model device, 2) established a mathematical model of sedimentation separation of particles in the centrifugal rotating flow field, 3) investigated the separation characteristics of the new dense media cyclone by combining experimental research and theoretical analysis, which revealed the separation variation patterns of raw coal difficult to select with high content heavy density components under different process parameters, 4) explored the factors affecting the dynamic stability of the working suspension in the flow field of the new heavy media cyclone and the discharge and transportation mechanism of heavy products. Results show that when the new dense media cyclone separates raw coal with high content of heavy density components, underflow heavy products exhibit stronger discharge capacity and higher processing capacity, while the centrifugal swirl field shows smaller density gradient distribution of suspension, more uniform density distribution, lower value of the difference between the underflow and the overflow density, as well as stronger stability of the suspension in the flow field. The feeding pressure is directly correlated with the dynamic stability of the suspension, separation accuracy and the discharge efficiency of heavy products. With increasing feeding pressure, the suspension discharged from the underflow and overflow port shows increased density difference, reduced possible deviation E value, improved separation accuracy and elevated amount of heavy product discharged. When the feeding pressure is 25 kPa, the actual separation density is 1.666 g/cm3, the possible deviation E value is 0.09 g/cm3, and the yield of heavy products is 75.23%, which provides new insights into the separation of raw coal with high content, heavy density components.

HZSM-5 molecular sieve is one of the commonly used catalysts for the alkylation of toluene with methanol to para-xylene (PX). This study introduces a one-step method to directly prepare microscale HZSM-5 catalysts with suitable pore structure and acidity. Specifically, this paper combined crystal seed regulation of the morphology of HZSM-5 and adjusted the Si/Al ratios of the precursor solution for HZSM-5 synthesis to regulate the acidic phase of the HZSM-5. It analyzed the phase composition, pore structure parameters, microstructure, and acidity of HZSM-5 molecular sieve through X-ray diffraction, N2 adsorption desorption, SEM, NH3 temperature programmed desorption, pyridine infrared spectroscopy, etc. This study investigated the catalytic performance of HZSM-5 in the alkylation of toluene with methanol to PX, and explored the effects of pore structure and acidity on the catalytic performance. Results indicate that in the hydrothermal crystallization method, the crystal seeds and aluminum content in the synthesis solution have a significant impact on the acidity and morphology structure of the HZSM-5 molecular sieve. The HZSM-5 (150)molecular sieve catalyst with 5μm grain size exhibits 60% PX selectivity and 11% toluene conversion rate in the evaluation reaction of toluene methanol alkylation due to its longer diffusion path and more suitable acidic sites. By fine-tuning the pores and acidic sites of HZSM-5 molecular sieve, the selectivity for PX has been effectively improved, providing new methods and approaches for the design of shape-selective catalysts.

This study aims to tackle the problem of frequent coal-rock dynamic events caused by local stress concentration in deep mining working face under high static stress environment. Specifically, by taking the deep working face of Hongqinghe Mine located in Xinjie Mining Area as an example for analysisthis paper investigates the geological conditions of No. 3-1coal seam that are affected by the mining method and the coal rock dynamic disaster events occurred during mining; utilizes numerical simulation to simulate the mining stress field and energy field of the stope; analyzes the potential coal burst instability area and mechanism of coal burst gestation and catastrophe in the stope during the mining of the No. 3-1103 working face; probes into the sources of catastrophic stress and influencing factors of coal-rock disasters in dangerous areas, puts forward targeted prevention and control measures. Results show that: ① the roof strata structure, goaf and coal pillar are the key factors influencing coal burst in the stope during the mining of the No. 3-1103 working face; ② the simulation results indicatethe location and characteristics of the coal burst instability area in the stope of the No. 3-1103 working faces, as well as the simulation outlines 5 strong coal burst areas and 11 medium coal burst areas presented in the stope; ③ Measures are proposed for coal burst during mining from the perspective of cutting off the dynamic load source, reducing static load stress concentration, and blocking the transmission of high concentration stress. Detailed measures include implementing multi-source prevention and control in areas with high static or high static+dynamic loads, implement pre-pressure off-load measures prior to mining, and local risk relief and coal burst prevention and reduction treatments during mining.

The labor force structure of intelligent coal mine has undergone profound changes as the coal industry transforms from traditional coal mines to intelligent ones. In this light, this study ① reviews the characteristics of the labor force in intelligent coal mine, ② analyzes the interaction mechanism of labor force and labor tools, ③ builds an adaptation model of labor force and labor tools. Specifically, it analyzes the deficiencies existing in the present personnel structure in intelligent coal mine construction from the perspective of labor quality structure, personnel training scale, regulations related to "intelligent replacement", coal mine data management professionals, and term shifts of posts in intelligent coal mines. This paper proposes detailed scheme and measures for career reshaping in intelligent coal mines, namely restructuring intelligent mining personnel structure, creating new posts and new types of work, updating policies and regulations, improving industry image and employee happiness, and improving talent training system.

When the coal-seams are multi-layered, the stress and permeability of the caving zone are disturbed again during the following coal seam mining. Repeated unloading and compaction cause caved coal and rock to break further in the caving zone, which in turn affects the migration of gas in goaf. This paper briefly summarizes prior research on caving zone internal stress, porosity, permeability and other parameters of the process of longwall face advancing. The forecast methods for calculating the stress and permeability of the caved zone during its compaction are listed. On the basis, this paper describes a laboratory experiment of the broken coal and rock in the caving zone of the gob in Huainan coal mine. The laboratory test results imply that the re-crushing, re-arrangement, and compressional deformation of particles in the loading process lead to a drastic drop in the caving zone porosity, which causes the permeability reduction. The permeability sensitivity to stress of broken rock (broken coal) samples was determined by their strength. The greater the proportion of coal samples in the combined coal and rock samples, the higher the permeability stress sensitivity and the smaller the permeability.With the increase of the cyclic times, the stress sensitivity gradually weakened. Based on laboratory experiments, the stress-permeability fitting model of the broken coal and rock in the caving zone during the group coal seam mining is proposed in this paper.

To solve the problems of low positioning accuracy, large deployment of reference nodes and large power consumption of nodes when wireless sensor network (WSN) positioning technology is applied in coal mine target positioning, this paper proposes a method of mine WSN target localization based on the compressed sensing(CS) algorithm. The method designs the target positioning in the offline phase and online monitoring phase based on the needs of mine target positioning and the characteristics of WSN. In the offline phase, the sparse matrix fingerprint database is constructed. In the online monitoring phase, the observation matrix and the measurement value vector are constructed, and combined with fingerprint database, the position signal of the target nodes is reconstructed to realize the accurate positioning of the mine targets. The simulation experiment compares the CS algorithm positioning with two traditional algorithm positioning. The results show that the positioning accuracy of the algorithm in this paper is higher, which can be controlled within 0.8m to meet the positioning requirement.

In order to smoothly implement gob-side entry retaining and mining without coal pillar in 3207 working face of Nanyang Coal Mine,Shanxi Province,this paper proposes to carry out advanced deep-hole blasting pre-splitting roof near gob side supporting wall.Through numerical simulation and field industrial test,the influence of deep-hole blasting roof cutting on surrounding rock stability of gob-side retaining roadway is studied.Based on the backdrop of retaining roadway along goaf in 3207 working face of Nanyang coal mine,a numerical simulation model was established,the displacement of roof and floor,wall and coal body of retained roadway,the stress distribution and variation of surrounding rock of retaining roadway were calculated.The numerical calculation shows that the variation of stress and displacement of surrounding rock in gob-side retaining roadway decreases greatly after roof cutting,and the stability of surrounding rock is improved significantly.The field industrial test results show that deep-hole blasting roof cutting can effectively eliminate the rotational extrusion damage of cantilever beam roof to surrounding rock of gob-side retaining roadway,and help to maintain the stability and integrity of gob-side retaining roadway structure.The research results of this paper can be used for reference in the design and construction of gob-side entry retaining project.

This study proposes to explore the effect of interface angles β on the triaxial mechanical properties of backfill and surrounding rock combined bodies(backfill-rock combined bodies)by conducting a triaxial compression experiment of backfill-rock combined bodies with interface angles β of 0°, 15°, 30°, 45° and 60°. This paper compared and analyzed the mechanical properties, failure characteristics and strength evolution patterns of the combined bodies with different interface angles. The experimental results show that: When β≤30°, the stress-strain curve of the combined bodies can be divided into four stages: pore compaction, elastic deformation, plastic deformation and failure development. Its failure characteristics are mainly compression shear failure of the backfill. With the increase of the interface angles, the combined bodies stress drops steeply after reaching the peak strength, without significant plastic deformation or failure development stage. Its failure characteristics gradually change from compression shear failure inside the backfill to sliding failure along the interface. The peak strength of the combined bodies first increases and then decreases with the increase of the interface angles, and peak strength reaches a maximum value when β=30°. Based on the theory of single weak plane, the interface critical angles for sliding failure of the combined bodies is 57° to 68°. Where β=60°, the combined bodies occurred sliding failure surface along the interface, and the results from theoretical calculation confirm the experimental results.

The Beishan area in Gansu province is the main pre-selected site for deep geological disposal of high-level radioactive waste, it therefore bears implications for the study of fracture seepage characteristics of granite caused by shear failure. This paper investigated the fractal modeling of the geometric and seepage characteristics of granite fracture sections under shear conditions, with the aim to explore the effect of the geometric characteristics of multi-scale rough fractures on the evolution of nonlinear seepage field in Beishan granite. Results show that the roughness height and aperture of rough fractures have complete self-similarity in the process of model scale change, whose distribution are always consistent in the process of spatial scale change. The seepage velocity field, gradient field and divergence field only demonstrate the continuation of local characteristics, in particular, the corresponding quantity fields at different scales are subject to normal distribution. As the observation scale increases, the spatial fluctuation in the field gradually decreases, the sharp mutations in the three fields gradually disappear and are smoothed. This indicates that the larger the observation scale, the greater the probability that the seepage of rough fracture is misjudged as the seepage of parallel plate, therefore the seepage characteristics of rough section would be more accurately described by taking the geometric scale into account.

North China coalfields are seriously affected by bottom aquifers. In order to accurately the depth of damage at the working face, this paper combined actual measurement with neural network prediction model in analysis. Firstly, DC method with special electrode cable is employed to observe the bottom plate damage depth of 15091 in the comprehensive mining face of Jiulishan mine; secondly, based on large-scale data, genetic algorithm is applied to optimize BP neural network. The prediction model of bottom plate damage depth is set up by optimizing parameters. The mean square error of the prediction model was 0.011, the average percentage error was 5.983 %, and the prediction error based on prediction set was below 10 %. These results indicate that the model can be used for predicting the bottom slab damage depth. Finally, the prediction model was used to analyze the effect of mining thickness and top cutting pressure relief on the depth of damage of the working face floor. Results show that under stratified mining, the depth of damage of the bottom slab is reduced by 77.84 % under cut top pressure relief than uncut top pressure relief; under integrated mining, the depth of damage of the bottom slab is reduced by 59.17 % under cut top pressure relief than uncut top pressure relief; and the effect of mining thickness on the depth of damage of the bottom slab is positively correlated.

As deep mining becomes prevalent in China's coal mining industry, coal-gas compound dynamic disasters pose increasing threat to the safety production of coal mines. This paper adopts the field data of Pingmei No. 8 coal mine for analysis, with the attempt to predict coal-gas compound dynamic disaster through convolutional neural network. Following the routine of the big data processing, we first employed Box-plot analysis and multiple interpolation method(MI)to clean the data. Combined with grey relation analysis(GRA), we established a coal-gas compound dynamic disaster index system. Then, principal component analysis(PCA)is used for dimensionality reduction of the data. Combined with the convolution neural network(CNN)in deep learning, we established the coal-gas compound dynamic disaster prediction model based on BMGP-CNN. The field data is used to compare and verify this model with BP, random forest(RF), support vector machine(SVM)and artificial neural network(ANN). It is found that BMGP-CNN model yields prediction results with satisfactory accuracy and quick convergence. The results offer implications for the prediction and prevention of coal-gas compound dynamic disasters.

When the surface strain field of concrete structure is measured by digital image correlation(DIC)technology under complex light conditions, the decorrelation effect of the pattern will be caused by the variation in light intensity. For this problem, the optimal light intensity suitable for DIC calculating and analyzing is studied, and the influence of light intensity variation on the measurement accuracy and calculation efficiency of DIC is explored by the traditional 2D-DIC measurement system. The experimental result shows that the average gray level of 190 is the optimal light intensity. The picture is used as the reference image at the optimal light intensity. The strain error increases exponentially when the light intensity increases, and the strain error increases linearly when the light intensity decreases. The computation time and the matching rate of calculation points are insensitive to the slight range fluctuation of light intensity, while the computation time of DIC will increase 1 to 3 times, and about 25 % of calculation points will match failed because of the extreme variation of light intensity. The accuracy of experimental results is verified by Combining them with the image quality assessment index. In order to get high-quality images, the green band-pass filter imaging system is established in this paper. It can stabilize the image's brightness and contrast when the external light varies seriously. The strain error and calculation efficiency are all close to the optimal light intensity when external ambient light changes seriously. Compared with the traditional 2D-DIC measurement system, The green band-pass filter imaging system can be better applied to measure in the outdoor environment.

The calcination process and the ratio of to calcium to silicon in raw materials are the key factors affecting the mineral composition and properties of natural water hard lime(NHL). This study prepared NHL was by different calcination processes using argillaceous limestone tailings with different chemical compositions as raw materials. This paper studied the mineral composition and compressive strength of the prepared NHL by a combination of orthogonal and single-factor tests, and analyzed the effect of calcination process and calcium-silica ratio on its performance. Results showed that: ① With the increase of calcination temperature, the content of CaO in NHL decreased, and the content of dicalcium silicate(Ca2SiO4, C2S)increased in NHL. ② Calcination temperature had the most significant effect on the mineral composition and compressive strength of NHL, followed by holding time and heating rate. ③ In the calcination temperature range of 1 000~1 100 ℃, the natural hydrostatic lime prepared by the given argillaceous limestone tailings meets the requirements of NHL2 and NHL3.5 strength grades. ④ When the calcium-silicon ratio is in the range of 3.55~6.76, the compressive strength of NHL decreases and then increases with the increase of calcium-silicon ratio, while the CaO content shows continuous increases.

Based on the theory of “cutting short-wall beam”,the automatic cutting-in coal-free pillar mining technology for roof-cutting pressure relief is widely used in engineering practice.However,due to the limitation of the numerical modeling of large deformation materials,the numerical simulation analysis of mine pressure distribution based on theory of truncated short wall beam has not been studied.In this paper,the numerical simulation model of NPR bolt/cable is established at the first based on the constant resistance mechanical mechanism of the NPR bolt/cable in the supporting process,achieving the goal of numerical and programmed calculation of large deformation materials .Then,based on the background of Hecaogou No.2 coal mine engineering,mine pressure in longwall mining is continuously monitored on-site.Finally,the numerical simulations and comparative analysis of mine pressure distribution by applying theory of truncated short wall beam on 1105 working face were made through FLAC3D program.The paper reveals the different characteristics of the distribution of abutment pressure under traditional technology and the working face of theory of truncated short wall beam,and this lays a theoretical foundation for the study of stress field distribution and the rule of temporal and spatial variation of rock mass structure using theory of truncated short wall beam.

Taking a coal mine in Shaanxi province as an example,this paper made an optimization study of its existing safe production management system.In full field investigation,the paper investigated the current situation of the safe production management system of the coal mine,and summarized the existing problems and analyzed the reasons for the formation of the problems.Based on the theory of scientific safety management and above problems,the optimization principles and goals of the safe production management system were clarified,and the corresponding optimization plan was put forward.The optimal design of the new safety requirements for the existing safe production management information system was proposed.A more complete supervision and inspection system was established,and a more scientific assessment process and evaluation system was developed.Finally,this optimization scheme was applied and verified in practice,and found that accident incidence was reduced significantly,and economic and social benefits were significant improved.

Aiming at path planning problem of the unstructured environment attributions for roadheader roadway this paper analyzes the attributes and behavior constraints of unstructured environments,and a dynamic random grid network model with constraint information was defined(C-G Net).The minimum cost modeling method was proposed by optimization of best path target point set through improved VSAPSO algorithm.Results shows that the model and algorithm proposed in this paper could effectively solve the problem of network path planning under dynamic random with minimum cost roadheader excavation.Its convergence rate and advance rate meet the requirements of roadheader rectification path planning,and the effectiveness and practicability of this method were verified.

Taking Fengtai County of Anhui Province as the research object, this paper used the ArcGIS to superpose the distribution of cultivated land resources, the distribution of coal resources and the construction of the mine, and analyze the compound characteristics of coal and agricultural production.The software MSPS based on the probability integral method, was used to predict the cultivated land evolution trends caused by coal mining subsidence in Fengtai County.Furthermore, the grain production reduction caused by the destruction of cultivated land is predicted, and the agricultural economic losses are estimated.The results show that the area of crop and coal production of Fengtai County accounts for 78.39% of the cultivated fields and accounts for 77.25% of the coal-bearing areas.The construction area of the coal mine in the county accounts for 50.66% of the compound area of the crop and coal production.With the constant exploitation of coal, the cultivated land of the compound area of crop and coal production would continuously reduce, and the extent of cultivated land damage could aggravate, which could seriously affect the local grain production, agricultural economic development and social stability.It is predicted that the areas of damaged the area of cultivated land in the mines closure accounted for 43.68% of the area of the total cultivated land, the grain reduction caused by the destruction of arable land in the mines could be 134.8 thousand ton, the losses of agricultural economy in the mines closure could be 0.304 billion yuan.These could result in a large number of farmers without cultivated land, and thus social conflicts could be caused, and the corresponding measures and suggestions are proposed in this paper.

Micro-pore structure affects the fluid storage and seepage in coal seams.In this paper, six samples from the Jurassic Yan'an Formation coal seam in the Shenmu area of the Ordos Basin were taken as the object of study.The pore distribution characteristics of coal seams were jointly characterized by NMR, CO2 adsorption and N2 adsorption at multiple scales, and the connectivity and homogeneity of microscopic pores were investigated by combining multi-scale joint characiterization with CT scanning.Results show that the micro-pores of coal are the main contributors to the specific surface area and pore volume, followed by meso-pores.There is a good uniformity in the pore size distribution of the micro-pores and meso-pores by combing NMR and adsorption, while considerable differences are found in the macro-pores.Displacement NMR and CT excel in reflecting the degree of connectivity, both of which are consistent in the characterization of connectivity.Parameters such as coordination number and seepage pore ratio can effectively reflect the degree of connectivity of the sample, whose patterns of connectivity is M6>M2>M12>M15>M10>M4.The saturation of bound water shows a satisfactory positive correlation with pore-throat ratio of coal samples.It can be seen that the pore structure has a great influence on the degree of fluid migration, which is the basis for studying and evaluating gas occurrence and seepage.

In order to study the mechanical response and failure characteristics of sandstone at the meso level, this paper first carried out indoor rock compression test and PFC2D uniaxial macro-meso parameter correlation numerical test based on parallel bond model.Then, the trial-and-error method is used to determine the order of the influence degree of each mesoscopic parameter on the macroscopic mechanical index, and the interaction analysis of significant factors is carried out.Finally, the regression analysis is used to establish the functional relationship between macroscopic and mesoscopic parameters.The main influencing factors of crack evolution and failure mode of rock samples are studied by using the control variable method.The results show that: ①The uniaxial compressive strength σc has a complex nonlinear relationship with parallel cohesion c, bond normal strength σc and bond internal friction angle φ.; ② Elastic modulus E has a polynomial relationship with bond modulus E * and bond stiffness ratio k *; ③ Poisson's ratio v is linear with k * and friction coefficient μ; ④The tensile strength σt has a good linear relationship with c and σc.; ⑤The crack evolution and failure mode of rock samples are mainly affected by the bond strength ratio σc/c, which is negatively correlated with the number of tensile cracks and positively correlated with the number of shear cracks. With σc/c increases, the failure mode of rock samples is characterized by tensile failure-conjugate failure-shear failure.The evolution law and failure form of uniaxial compression σ-ε in laboratory test and numerical simulation are basically the same.

To master the influence law of complex landform such as the surface mountain and the valley area between the mountains on the underlying coal rock stress, this study constructed a calculation model of the vertical stress of the coal strata under the mountain through theoretical analysis.Taking the 50205 working face of Hecaogou coal mine as example for analysis, This paper studied the complex landform on the underlying coal rock load characteristics and stress transfer law.Results show that: mountain load has significant stress effect on shallow coal seam.In the horizontal direction, the influence range is negatively correlated with the mountain slope, and the coefficient of influence range is positively related to the mountain slope.The effect of mountain on the vertical stress of the underlying coal seam can be divided into three stages: initial effect, intense growth effect and slow growth effect.The vertical stress superposition value of the underlying coal strata in the gully region firstly increases and then decreases with the change of depth.Moreover, when the distance between two adjacent mountains increases to more than.1.25 times of the width of the mountain bottom, the effect of stress superposition is very small and can be ignored.As the distance between adjacent mountains gradually increases, an inverted triangle area with insignificant stress superposition is formed in the coal strata under the gully area.