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Monitoring and preventing coal–rock dynamic disasters are essential for ensuring sustainable and safe mining. Induced charge monitoring, as a geophysical method, enables sustainable monitoring of coal–rock deformation and failure. The induced charge signal contains crucial information regarding damage evolution, making it imperative and important to explore its temporal characteristics for effective monitoring and early warnings of dynamic disasters in deep mining. This paper conducted induced charge monitoring tests at different loading rates, investigating the multifractal characteristics of induced charge signals during the early and late stages of loading. It proposed the maximum generalized dimension D(q)max, multifractal spectrum width Δα, and height difference Δf as multifractal parameters for induced charge signals. Additionally, quantitative characterization of coal damage was performed, studying the variation patterns of signal multifractal characteristic parameters with coal damage evolution. This study revealed the induced charge signal of the coal body multifractal characteristics in the whole loading process. In the late loading stage, the double logarithmic curve demonstrated some nonlinearity compared to the previous period, indicating the higher non-uniformity of the induced charge time series. D(q)max and Δα in the late loading stage were higher than those in the early stage and increased with loading rates. As coal damage progressed, there were significant jumps of D(q)max in both the early and late stages of damage, with larger jumps indicating richer fracture events in the coal. The width Δα showed an overall trend of increase–decrease–increase with coal damage evolution, while the height difference Δf fluctuated around zero in the early stage of damage development but increased significantly during severe damage and destruction. By studying the multifractal characteristics of induced charge signals, this study provides insights for the early identification of coal–rock dynamic disasters. [ABSTRACT FROM AUTHOR]

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.

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Delayed coal and gas outbursts strongly relate to the transformation from creep deformation to rapid failure after extracting operations. However, the quantitative characterization of creep deformation and instability failure process of gas-bearing coal is insufficient. Hence, the long-term strain of coal samples under loading was measured under different axial, confining and gas pressures to analyse the creep damage, nonlinear deformation and catastrophic failure of the coal. It is found that the degree of creep deformation of the coal samples is closely related to the applied stress. When the applied stress is lower than the long-term strength of the samples, only decelerated and steady-state creep deformations can occur in the coal samples. The steady-state creep rate increases in the form of a power function with the creep time. However, accelerated creep failure occurs during long-term loading at a stress level exceeding the long-term strength of the sample. The gas pressure effects significantly change the creep characteristics of coal. The steady-state creep rate of coal without gas exponentially increases with increasing axial pressure, while that of gas-bearing coal linearly increases. The adsorption-induced expansion stress is proposed based on the principle of effective stress of porous media. A triaxial creep damage and catastrophic failure model for gas-bearing coal is constructed by considering the influences of damage accumulation on creep deformation. This model can quantitatively characterize the creep damage process of a coal mass under specific conditions. [ABSTRACT FROM AUTHOR]

Disturbance stresses can cause deformation and damage to a tunnel's rock, potentially threatening the mine's safety. This paper investigates the effects of disturbance damage on the main inclined shaft due to the excavation of an electromechanical chamber in a deep inclined shaft at Yuxi Mine. Specifically, a numerical model was constructed using Midas GTX NX and Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D) to match the actual engineering conditions, and to reveal the stresses and deformations in the surrounding rock of the main inclined shaft before and after the excavation of the main inclined shaft, the electromechanical chamber and the head chamber. The results revealed that the surrounding rock stress around the main inclined shaft is significantly influenced by excavation disturbance. The bottom bulge occurred due to the unstable vertical and shear stresses in the bottom coal bed moving into free space. After the excavation of the electromechanical chamber, the maximum displacement of the floor can be increased from 0.35468 m to 0.64301 m, nearly doubled, and a large area of surrounding rock deformation occurs in the inclined shaft falling roadway. Affected by excavation disturbance, the maximum deformation of floor can reach 1.06 m, with a wide fluctuation range. The main area of damage to the surrounding rock was identified, except for the main inclined shaft, which occurred near the intersection of the inclined shaft and the drop level location. This area is mainly affected by superimposed tensile stress damage, prone to large area floor heave and spalling. The research content is expected to provide certain theoretical support in taking measures to deal with the deformation and failure of the surrounding rock in a main inclined shaft. [ABSTRACT FROM AUTHOR]

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.

Disturbance stresses can cause deformation and damage to a tunnel’s rock, potentially threatening the mine’s safety. This paper investigates the effects of disturbance damage on the main inclined shaft due to the excavation of an electromechanical chamber in a deep inclined shaft at Yuxi Mine. Specifically, a numerical model was constructed using Midas GTX NX and Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D) to match the actual engineering conditions, and to reveal the stresses and deformations in the surrounding rock of the main inclined shaft before and after the excavation of the main inclined shaft, the electromechanical chamber and the head chamber. The results revealed that the surrounding rock stress around the main inclined shaft is significantly influenced by excavation disturbance. The bottom bulge occurred due to the unstable vertical and shear stresses in the bottom coal bed moving into free space. After the excavation of the electromechanical chamber, the maximum displacement of the floor can be increased from 0.35468 m to 0.64301 m, nearly doubled, and a large area of surrounding rock deformation occurs in the inclined shaft falling roadway. Affected by excavation disturbance, the maximum deformation of floor can reach 1.06 m, with a wide fluctuation range. The main area of damage to the surrounding rock was identified, except for the main inclined shaft, which occurred near the intersection of the inclined shaft and the drop level location. This area is mainly affected by superimposed tensile stress damage, prone to large area floor heave and spalling. The research content is expected to provide certain theoretical support in taking measures to deal with the deformation and failure of the surrounding rock in a main inclined shaft.

In order to quantitatively study evolution law between temperater parameter of infrared radiation and coal-rock damage law under uniaxial compression, temperature data of infrared radiation during coal-rock failure process was collected and analyzed. A coal-rock damage model was established according to damage mechanics theory, so as to obtain relationship between the maximum infrared radiation temperature (MIRT) and coal-rock damage. The results show that: ① The MIRT-time curve has a good correspondence with load-time curve of the coal-rock under loading, and the MIRT can reflect the damage of coal-rock under loading. ② The coal-rock damage model based on infrared radiation temperature accumulation can well reflect evolution, development and failure of cracks in the coal-rock under uniaxial compression. ③ The correlation coefficient between calculated stress based on MIRT accumulation and measured stress is more than 0.8, which is highly correlated, and peak of the calculated stress-strain curve is ahead of the one of the measured stress-strain curve.

Uniaxial compression test was conducted on pre-cracked coal sample, and infrared radiation temperature and its change rule of the pre-cracked coal sample under loaded breaking were researched. The experimental results show that infrared radiation temperature curve will mutate in process of loaded breaking of the pre-cracked coal sample, and the infrared radiation temperatures of the pre-cracked coal samples with different angles will suddenly increase during main rupture. The mutation rate of infrared radiation temperature increases first and then decreases with increase of pre-cracked angle during main rupture, and the mutation rate of infrared radiation temperature of the pre-cracked coal sample with 45° is the largest. The change rule of infrared radiation of the pre-cracked coal sample is closely related to load and pre-crack, which can reflect internal rupture of macroscopic defective coal sample under load.

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study explored the occurrence of coal-rock dynamic disasters during the low-temperature oxidation of coalbed methane (CBM) reservoirs for different coal ranks by investigating the dynamic development of pores in coal during low-temperature oxidation. This research monitored dynamic changes in the diameters and numbers of pores in different rank coals during low-temperature oxidation using nuclear magnetic resonance (NMR) and the P-wave rock measurement system. Microscopically, by utilizing industrial component analysis technology and gas chromatography, this study determined the dynamic changes occurring in the composition of coal and the concentrations of representative gases in the low-temperature oxidation of different rank coals. By adopting a new comprehensive index K, which is a combination of the coal-rock hardness (f) and the initial velocity (△p) of a gas emission, to predict a gas outburst, the authors predicted coal-rock dynamic disaster hazards in the low-temperature oxidation of different rank coals. The experiment showed that there are similarities and differences in pore development during the low-temperature oxidation of different rank coals. The similarities are illustrated in the consistencies underlying fracture development. Specifically, in the early stage of low-temperature oxidation of coal (30–130 °C), due to the evaporation of water, the dehydration of compounds containing crystalline water and the decomposition and volatilization of volatiles, micro-pores in coal expand and connect to form meso-pores. In the late stage of oxidation (130–230 °C), the macromolecular compounds and volatiles in coal oxidize and decompose such that meso-pores expand and connect to form macro-pores and micro-fractures. However, as the metamorphic degree of the coal increases, the oxidation resistance and thermal stability of the coal improves, and the initial temperature for the development of pores with the same diameter increases. Based on the concept of the comprehensive prediction index K, the probability of a coal-rock dynamic disaster occurring in a CBM reservoir gradually increases as the oxidation temperature increases. The lower the metamorphic degree of the coal, the faster the growth rate. Therefore, the oxidation temperature at which the probability of a coal-rock dynamic disaster increases by 50% is used as the critical temperature for taking fire prevention measures, i.e., 90 °C and 130 °C for lignite and bituminous coals, respectively. [ABSTRACT FROM AUTHOR]

In order to analyze influence of each operation in mining process on measurement of electromagnetic radiation, a test was carried out on working face in Changgouyu Coal Mine and electromagnetic radiation monitoring signals of each operation were analyzed quantitatively. The results show that online electromagnetic radiation monitoring signals are mostly influenced by electrical equipments such as winch, scraper conveyor and bell which are main interference resources, and less interferenced by non-electric operation such as pillar compression and personnel moving. The research provides reliable basis for eliminating influence of interference sources while using electromagnetic radiation critical value method to judge coal-rock dynamic disaster at field.