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The mining of thin coal seam resources is seriously affected by the overlying coal seam gas. The detection of three zones of goaf roof is of great significance to the safety production. In this paper, we carried out loading coal and rock resistivity testing experiment, analyzed the loading damage in the process of coal and rock resistivity change and distribution, and carried on the theoretical analysis and numerical simulation of overlying strata three zones according to the actual embedded depth, and then carried out field test. Direct current method has been used to test the forward three-zone apparent resistivity distribution. The main conclusions are as follows: the resistivity changes due to the crack propagation of coal samples, and the resistivity surge point corresponds well with the failure point of coal and rock; in the process of coal and rock failure under load, there are abnormal areas in the resistivity cloud diagram under load, and it migrates with the uneven deformation of coal and rock under load; the collective subsidence of the goaf after the roof is cut in the coal seam mining will form a large sectioned area in thefracture area of the upper part of the goaf. There are large cracks in this part of the sectioned area, and it will extend to the roof rock of the return air roadway, resulting in the increase of cracks in the rock; the electrical detection results show that the horizontal distance from the working face to the caving zone is about 20 m, and the influence resistance value of the fracture zone becomes larger and its height is 17 m, which is consistent with the theoretical calculation and numerical simulation results.

As an important basic energy and industrial raw material in China, the safe mining of coal is the key to ensuring the national energy security and supporting the stable development of economy and society. With the gradual depletion of shallow coal resources, deep mining has gradually become the new normal of coal resource development in China, and the risk of coal- rock dynamic disasters has risen, which seriously restricts the safety and efficiency of coal mining, and has caused adverse effects on the sustainable development of coal industry. Accurate and reliable monitoring methods are considered as the prerequisite for the prevention and control of coal-rock dynamic disasters. Geophysical methods are widely used in the early warning of coal and rock dynamic disasters by sensing the acoustic, electrical, magnetic and other physical signals released during the deformation and failure process to retrieve the damage and failure state of coal and rock mass. Among those methods, the electromagnetic radiation method is a non-invasive, non-destructive, real-time and strong precursory technique suitable for the development requirements of mine informatization and intellectualization. Therefore, the development of electromagnetic radiation monitoring technology is of great significance for the prevention and control of coal and rock dynamic disasters and can provide important technical support for the construction of intelligent mines. The research achievements of electromagnetic radiation theory and technology are summarized in three aspects: experimental phenomena, mechanism models and technical methods. The discovery process of electromagnetic radiation phenomenon is reviewed. The signal characteristics, influencing factors, electromechanical coupling effects and other electromagnetic radiation characteristics of coal-rock are analyzed. According to the correlation between typical electromagnetic radiation mechanism models, stress action and crack propagation process, a classified review is made. The existing coal and rock electromagnetic radiation monitoring and early warning equipment and technical methods are then briefly introduced. On this basis, the new progress made in recent years is described in detail, including the research on vector characteristics of electromagnetic radiation, micro-scale verification of electromagnetic radiation mechanism, and electromagnetic positioning technology of coal-rock fracture. It summarizes the two current theoretical and technical research bottlenecks that the mechanism is not fully revealed and the location of disaster-prone areas cannot be achieved. Finally, a new target for the future development of electromagnetic radiation theory and technology is proposed.

Compared with the energy dissipation of coal and rock failure, the more intuitive stress drop has certain practical significance for assisting the study of coal and rock failure characteristics and variation law of geophysical signals. And the stress drop is the macroscopic manifestation of energy dissipation. Most of the current research on energy dissipation and stress drop is only for one-sided research, without a comprehensive study on the relationship between the two. The relationship between the two is not clear, which restricts the application of the stress drop index. In order to solve the above problems, YAW−600 microcomputer controlled electro-hydraulic servo pressure testing machine is used to carry out uniaxial compression experiments on coal samples. The evolution characteristics of energy dissipation index and stress drop index in the whole process of coal sample failure under load and the relationship between them are studied and analyzed. Based on theoretical analysis, the relationship between energy dissipation index and the product of stress level and stress drop index is further studied. The results show that the energy dissipation index and stress drop index in the uniaxial compression failure process of coal sample have good response to the significant fracture of coal sample. And the indexes are in the same order of magnitude in numerical value, but they are not completely proportional. The energy dissipation rate is linearly related to the product of stress level and stress drop rate. And the energy dissipation is linearly related to the product of stress level and stress drop. The goodness of fit is 1 and 0.997 5 respectively. Compared with the energy dissipation index, the more intuitive product of stress level and stress drop index is more sensitive to the significant damage of coal samples, and has a burst characteristic. The research results clarify the relationship between energy dissipation and stress drop, and provide a certain theoretical support for the application of stress drop index. The relationship can be used for in-depth research on the coal rock failure characteristics and the variation law of geophysical signals such as acoustic emission, electromagnetic radiation and infrared radiation.

In order to solve the problem of difficult prevention and control of coal and gas outburst in thin coal seam, the distribution characteristics of effective extraction area in thin coal seam are analyzed. Due to the limitation of the thickness of the thin coal seam, the expansion of the effective gas extraction area in the vertical direction is hindered, and it tends to extend in the horizontal direction, resulting in the effective extraction radius in the horizontal direction is much larger than the thickness of the coal seam. The effective extraction area is elliptically distributed. The gas seepage field mainly focuses on the direction and inclination of the coal seam. According to the characteristics, it is pointed out that the outburst elimination technology of shield tunneling in middle roadway based on the coal seam extraction mode can make the extraction area connected together. The technology is more suitable for gas extraction in thin coal seam. This paper analyzes the advantages and technical principles of applying the outburst elimination technology of shield tunneling in the middle roadway to block outburst elimination in thin coal seam. The gob-side entry retaining technology is adopted to make the return airway roadway of the previous working face as the air inlet roadway of the next working face. The gas extraction boreholes are constructed ahead of the air inlet roadway, and the extraction range covers and exceeds the predetermined middle roadway by more than 20 m. The gas extraction is used to eliminate the outburst danger of the middle roadway. tunneling the middle roadway. The gas extraction boreholes are constructed at the predetermined position in the middle roadway to the return airway roadway, and the extraction range covers and exceeds the predetermined return airway roadway by more than 20 m. The gas extraction is used to eliminate the outburst danger of the middle roadway. Finally, the return airway roadway is excavated to form the working face. Taking the thin coal seam of 9305 working face of a mine as the research object, the numerical simulation is carried out. The results show that when the extraction time is between 10 d and 30 d, the increase of the effective extraction radius is the largest. With the increase of the extraction time, the increase of the effective extraction range gradually decreases. When the borehole spacing is 3 m, the effective extraction radius between the two holes is almost tangent, and the extraction effect is the best. The extraction pressure can basically make most of the coal seam gas to be effectively diffused, resolved and passively extracted. The gas extraction in the middle roadway reduces the gas pressure between the return airway roadway and the progressive middle roadway area effectively. The field measurement results show that the optimal extraction borehole spacing for shield tunneling in the middle roadway of outburst coal seam in 9305 working face is 3 m, the borehole diameter is 94 mm, the effective extraction diameter is not more than 5 m, and the drilling depth is 107 m. The outburst elimination technology of shield tunneling in middle roadway reduces the gas volume fraction of the thin coal seam by about 70%, and the outburst elimination effect is remarkable.

In order to explore the rule of the duration of the acoustic electric signal when the coal sample is damaged by loading, the full waveform synchronous acquisition of the acoustic electric signal during the uniaxial loading failure process of the coal sample under different loading rates is carried out, the time sequence characteristics of the acoustic electric signal during the coal sample failure process are compared and analyzed, and the waveform characteristics and duration of the acoustic emission and electromagnetic radiation in the complete failure stage are emphatically analyzed. The results show that: in the process of uniaxial loading failure of coal samples, the response of acoustic and electrical signals has a good synergy, the higher the loading rate is, the denser and stronger the acoustic and electrical signals are generated during the main failure; the results show that the AE signal changes with the loading stage, and there is no obvious AE signal in the compaction and elastic stage; in the accelerated failure stage, the AE signal is gradually enriched and the amplitude increases; in the complete failure stage, the amplitude of the AE signal reaches the maximum when the main failure occurs, and decays synchronously after the peak; under different loading rates, the duration of AE signal is in millisecond level, and the duration of AE is 2 to 3 times longer than that of electromagnetic radiation. With the increase of loading rate, the duration of AE signal and electromagnetic radiation increase significantly, and the multiple increases with the increase of loading rate.

In order to solve the problem that there are few researches on the acoustic emission characteristics in the process of coal rock expansion and fracture, experiments on coal rock expansion and fracture are carried out to analyze the change law of strain and acoustic emission signals during the whole process of coal rock expansion and fracture. The results show that: ① the coal-rock expansion and fracture process can be divided into micro-fracture stage (Ⅰ), macro-fracture generation and expansion stage (Ⅱ) and splitting stage (Ⅲ). ② the strain evolution of coal and rock samples in the expansion process is consistent, showing the trend of 'slow change→acceleration→extreme value'. However, the acoustic emission signals of the two samples at each stage are quite different. ③ the acoustic emission ringing counts are more abundant in the coal samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts increase exponentially near stage Ⅲ; while the acoustic emission ringing counts are less in the rock samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts show a 'sudden increase - calm' trend near stage Ⅲ. ④ there is deformation localization in the process of both coal and rock expansion and fracture. The sudden change of strain variation coefficient and the increase of acoustic emission peak frequency range can be used as the precursor characteristics of coal rock expansion,fracture and instability. The research results can provide a basis for monitoring and early warning of coal rock fractures and other projects.

In order to give an accurate warning of coal and gas outburst disaster, a triaxial compression wave velocity test system of coal and rock with gas outburst was built. The coupling relationship between the axial pressure, confining pressure, the gas pressure and wave velocity of coal and rock with gas was studied under the laboratory conditions, and the mathematical model of wave velocity and pressure was established. The results show that: when the load of the sample is constant, with the increase of the gas pressure, the longitudinal wave velocity will decrease sharply at the beginning, and then tend to be stable, showing a linear negative correlation; when the confining pressure and the air pressure conditions are constant, the wave velocity of the sample will increase rapidly after the axial pressure is applied at the beginning, and then the wave velocity tends to be flat and increases linearly, showing an exponential function relationship; when the air pressure and the confining pressure strip, with the increase of confining pressure, the longitudinal velocity of the specimen increases uniformly and linearly, and the mathematical model fitted by the three test results has a high correlation coefficient.

The analysis of time-domain characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) signals in process of rock failure under load mostly draws qualitative conclusions from amplitude, ringing count, energy and other parameters, without directly giving time-domain correlation of AE and EMR signals, and parameters used in frequency-domain characteristics analysis of AE and EMR signals are relatively simple. In view of the above problems, monitoring experiment of AE and EMR signals of rock samples under uniaxial compression was carried out, and time-frequency characteristics of AE and EMR signals in different stages of rock failure under load were analyzed. The results show that: ① In compressionstage and elastic stage, amplitude of AE and EMR signals is basically zero. In accelerated failure stage, amplitude of AE and EMR signals increases gradually and the number of signals increases gradually. In stage of complete failure, amplitude of AE and EMR signals increases and decreases almost at the same time. When load reaches the peak value, amplitude of AE and EMR signals reaches the maximum at the same time. Amplitude of AE signal is larger than that of EMR signal in the whole process of failure under load. ② In accelerated failure stage, AE and EMR signals are significantly correlated. In stage of complete destruction, AE and EMR signals are highly correlated. In the whole process of failure underload, variation trend of AE and EMR signals with time is basically the same, and AE and EMR signals are highly correlated in time-domain. ③ In accelerated failure stage and complete failure stage, EMR signals are mainly low frequency and very low frequency signals. Compared with EMR signal, AE signal has wider frequency band and larger amplitude of main frequency. Main frequency concentration range of AE and EMR signals is similar but not completely consistent. Amplitude of main frequency of AE and EMR signals in complete failure stage is larger than that in accelerated failure stage.

Influence of concentration, particle size and ignition energy of coal dust on secondary explosion characteristic of coal dust were studied by use of 20 L spherical explosion device, and the secondary explosion characteristic of coal dust was compared with the first explosion characteristic of coal dust. The results show that with the increase of coal dust concentration, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust increase firstly and then decrease, the maximum pressure difference between the first explosion and secondary explosion decreases firstly and then increases, and the maximum rising rate difference of pressure between the first explosion and secondary explosion decreases firstly, then increases and decreases lastly; with the decrease of coal dust particle size, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust gradually increase, the maximum pressure difference and the maximum rising rate difference of pressure between the first explosion and secondary explosion increase firstly and then decrease; with the increase of ignition energy, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust, and the maximum pressure difference and the maximum rising rate difference of pressure between the first explosion and secondary explosion increase; the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust is smaller than that of the first explosion; coal dust concentration is the main influence factor on the characteristic difference between secondary explosion and the first explosion of coal dust.

For the demand of automation and accuracy of coal and gas outburst early warning, a remote intelligent monitoring and warning system for coal and gas outburst was developed. The system constitution was introduced as well as key technologies including signal monitoring, interference recognition, signal transmission and early warning rules. The system takes sound acoustic emission, electromagnetic radiation and gas concentration as early warning indexes, and realizes remote monitoring and comprehensive early warning of sound acoustic emission, electromagnetic radiation and gas signals during outburst evolution process. Meanwhile, the system can automatically recognize and filter interference signals according to opening or stopping information of electromechanical equipments, so as to improve early warning accuracy of coal and gas outburst. The application result shows the system has high early warning accuracy, which can capture coal and gas outburst risk information in advance of 8-24 hours.

In order to research the problem that mining underlying No.8 coal seam can alleviate strong strata behavior during mining No.3 coal seam or not, a far distance lower protective seam mining scheme was simulated by use of FLAC3D software, and stress peak value, stress distribution and plastic range were analyzed during mining process of the protected No.3 coal seam before and after mining the lower protective No.8 coal seam. The research results show that with the lower protective No.8 coal seam advancing, inclined stress of working face of the protected No.3 coal seam represents 'M' shape, namely both ends of coal body shows stress concentration, and stress in middle region is lower, so as to make surrounding rock of the No. 3 coal seam working face roadway, which is arranged in central pressure relief area, get pressure relief with different degree. After mining the lower protective No.8 coal seam, the stress peak value of the protected No.3 coal seam working face is reduced about 18%, and mining influence distance is shorted about 10 m. Meanwhile, stress concentration degree is weakened, and new plastic zone does not appear in coal body of the working face.

Surface potential of coal rock during water-inrush process was tested through a simulated experiment system for surface potential of coal rock, and variation rule of the surface potential of coal rock during water-inrush process was researched. Following conclusions are gotten: The surface potential of coal rock has significant spatiotemporal response characteristics for water-inrush evolution, and can reflect internal rupture and crack expansion conditions of coal rock. Water bursting evolution is divided into three periods, namely incubation period, crack expanding period and systematical water-inrush period. The surface potential signals are relatively stable during incubation period, and fluctuate during crack expanding period and systematical water-inrush period. The surface potential signal level is usually different in different positions. In the same position, the surface potential signal level has positive correlation with pore water pressure or breaking intension of coal rock.

Numerical simulation was conducted for hydraulic fracturing process in coal seam according to solid-liquid coupling equations and Mohr-Coulomb principle. The evolution of seepage field, stress field and fracture field (three fields) during process of crack propagation in coal seam was analyzed respectively. The results show that the three fields are changing dynamically during the process of hydraulic fracturing. The fracture is motivated to expand by pore water pressure, as a result of which, crack damage increases, seepage field centering to the fracture expands gradually, and high stress area and low stress area are developed from original stress field, and two regimes of low stress and high permeability field in a vertical direction of main fracture are ultimately formed. All of the above contribute to an effect of pressure relief and permeability improvement.

By establishing real-time monitoring system of resistivity variation regularities of loaded coal, real-time resistivity variation law of natural raw coal samples and raw coal samples with different moisture content in uniaxial compressive failure process was tested and studied, and the effect of porosity of the process on the resistivity was analyzed. The testing results show that resistivity of natural raw coal samples increases dramatically when a large-scale destruction of rupture crack, although resistivity of raw coal samples with different moisture content also increases during burst damage, but compares to the natural raw coal samples is more gentle; porosity of raw coal samples with moisture content has a significant impact on resistivity change in damage process, resistivity and porosity change of raw coal samples with moisture content is negative linear correlation before severe damage.