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A novel approach for mapping induced fractures and associated lineaments has been introduced based on microseismic data, and thus their contribution towards identification, and prediction of the risk zones which may lead to a collapse or rockburst in a coal mine. By taking Tashan Coal Mine (TCM) in Datong coalfield of China as an example, the real-time microseismic data was acquired for a period of 7 months. The microseismic data was processed using standard processing schemes followed by source location and parameters estimation. The proposed approach utilizes microseismic events, trace them to map the induced fractures, and based on their network to interpret associated lineaments. Based on the configuration, geometry, and network, thousands of fractures were identified which vary in length. Regional lineaments have been interpreted based on the orientation of these fractures. The fractures and lineaments distribution were further correlated with computed microseismic energy distribution. The spatial distribution of microseismic energy helped in identification of a geological discontinuity (fault) that clearly separates the study area into northern and southern parts. The reactivation of this fault may pose significant threats to mass stability, life, and property. The northern half is characterized by more and short length fractures while southern by prolonged and fewer fractures. The upper northern half is dominated by high energy ( ≥ 50, 000 J), while the lower part is characterized by variable energy pattern (22,000 to 40, 000 J). It is inferred from the energy-lineaments correlation figure, the northern half describes relatively stronger rock type in comparison to the southern part suggesting different rock deformational behavior. The fractures and lineaments converging towards a single point define risk zones where future collapse or rockburst can be expected. This identification of risk zones provides a strong basis for the real-time prediction of future catastrophic hazards in the coal mines. This study may benefit global underground engineering researchers for hazards prediction and establishing of the early warning systems.

Rockburst has become a main problem affecting the safety and efficiency of coal mine production. Early warning of it is essentially important for safety management. The dynamic and static load sources of rockburst, induced by multi-coal seam mining, are more complex, making rockburst prediction more difficult. The problem of rockburst early warnings in multi-seam mining was addressed by establishing a regional local integrated rockburst monitoring and early warning method based on the following criteria. (i) In regional space, the microseismic (MS) frequency ratio index and dispersion index were used to predict the regional dynamic load. (ii) In the local excavation and mining space, the risk degree of local static load concentration was characterised by the overrun amplitude indexes of electromagnetic radiation (EMR) intensity and pulse. (iii) According to the predicted spatial location of dynamic load and the attenuation law of regional dynamic load, the influence weight of the regional dynamic load on the excavation and mining space was determined. Based on this, the danger degrees of regional dynamic load and local static load were superposed to realise the regional local integrated warning of rockburst. This prediction method was applied for predicting rockburst in the Xinzhouyao mine, and the result indicated that the method can effectively predict the occurrence of dynamic load, the risk degree of local static load and rockburst induced by multiple types of dynamic and static loading combined together. The reliability of this prediction method was verified by records of roadway deformation and rockburst, and detection results from passive velocity tomography.

The stress and gas pressure in deep coal seams are very high, and instability and failure rapidly and intensely occur. It is important to study the infrared precursor characteristics of gas-bearing coal instability and failure. In this paper, a self-developed stress-gas coupling failure infrared experimental system was used to analyse the infrared radiation temperature (IRT) and infrared thermal image precursor characteristics of gas-free coal and gas-bearing coal. The changes in the areas of the infrared temperature anomalous precursor regions and the effect of the gas on the infrared precursors were examined. The results show that high-temperature anomalous precursors arise mainly when the gas-free coal fails under loading, whereas the gas-bearing coal has high-temperature and low-temperature anomalous precursors. The area of the high-temperature anomalous precursor is approximately 30%–40% under gas-bearing coal unstable failure, which is lower than the 60%–70% of the gas-free coal. The area of the low-temperature abnormal precursor is approximately 3%–6%, which is higher than the 1%–2% of the gas-free coal. With increasing gas pressure, the area of the high-temperature anomalous precursor gradually decreases, and the area of the low-temperature anomalous precursor gradually increases. The high- and low-temperature anomalous precursors of gas-bearing coal are mainly caused by gas desorption, volume expansion, and thermal friction. The presence of gas inhibits the increase in IRT on the coal surface and increases the difficulty of infrared radiation (IR) monitoring and early warning for gas-bearing coal.

Close extra-thick coal seams are subject to the broken overburden of mined coal seams, and the deformation and damage of the roadways is serious, which affects the safe operation of the mine. To reduce the deformation and damage of the roadways, this paper studied the deformation and damage law of the gob-side roadway in close extra-thick coal seams through numerical simulation and field monitoring, compared and analyzed the deformation and damage characteristics of the roadway under different reinforcement support methods, determined the optimal reinforcement support method, and carried out field verification. The obtained results indicated that the deformation and damage of the gob-side roadway showed asymmetric characteristics. The large deformation of the coal body in the deep part of the roadway wall is an important reason for the continuous occurrence of roadway wall heave in the coal pillar. Under the action of unbalanced support pressure, the floor is subject to the coupling effect of horizontal extrusion pressure and vertical stress that cause extrusion mobility floor heave. The horizontal and vertical displacement of the coal pillar side of the roadway under different support methods is much larger than that of the solid coal side. Increasing the anchor cable length and fan-shaped arrangement can improve the support effect. Grouting at the coal pillar side can significantly improve the bearing capacity and stability of the coal pillar. The effect of floor grouting is much better than the anchor cable in controlling the floor heave. The integrated reinforcement method of anchor cable + coal pillar side grouting + floor grouting has the best effect with the least horizontal and vertical deformation. The research results are of great significance for ensuring the stability of similarly endowed roadways.

Coal and rock dynamic disasters have been the main concern in underground engineering because these seriously threaten the safety of miners and industrial production. Aiming to improve the EMR and AE monitoring technology, the refined nonlinear characteristics of EMR and AE during coal splitting failure are studied using Hilbert-H and multifractal theory, and valuable information pertaining to coal fracture law contained in EMR and AE waveform was revealed. The results show that the EMR and AE of coal splitting failure are related to the process of coal crack propagation. They possess the same initiation time and frequency band, however, the signal duration of EMR is comparatively longer than AE, and the main frequency of AE is higher than EMR. The EMR of coal splitting failure has the same excitation source as AE; nonetheless, the excited forms display different behavior. In terms of signal duration, the distribution of EMR signal is relatively uniform, the proportion of large-signal is less, the amount of information is more than that of AE, and the multifractal characteristics are more complicated. During the coal splitting failure, AE is mainly generated in the process of wall vibration caused by crack propagation, while the generation of EMR includes piezoelectric effect, charge separation, free charge vibration, charge neutralization and other processes, making EMR more complicated than AE and has a relatively low frequency. The research provides an effective method for studying nonlinear refinement characteristics of coal EMR and AE, and can provide an important basis for the study of the mechanism of EMR generation.

To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that microseismic events occur and accumulate frequently in the surrounding rock and some overlying key layers of the GSR. Large deformation is experienced in the middle part of roadway near the solid coal side, the middle and upper parts of the roadway near the coal pillar side, and the roadway floor. The overlying strata of the GSR are fractured to form a composite structure as “low-level cantilever beam and high-level masonry beam”. The coal pillar is squeezed and effected by the composite beam structure and the rotation moment M, causing serious bulge in middle and upper part of the coal pillar side. The stability of the solid coal side of the roadway is affected by the stress transferred from gangue contact point. Numerical simulation shows that the immediate roof and key layer breakage are induced by the mining of the 30,501 working face. Shear and tension failures happen in the GSR due to overburden subsidence and rotary extrusion. The stress and displacement at the middle and upper of the roadway on the coal pillar side are larger than the other area. Compared with the solid coal side, the coal on the coal pillar side is obviously more fractured, with a lower bearing capacity. The peak stress in the coal pillar shows up 2 m away from the roadway, which is close to the length of bolt support. The mining-induced stress and the stress transferred from gangue contact point are the direct reasons for solid coal bulge beside the roadway. The peak stress on the solid coal side is located 7 m away from the roadway, at the gangue contact point where overburden fractures. The overburden strata loads and the transferred stress near the gangue contact point are transferred from the sides to the roadway floor. Their coupling effect with the in situ horizontal stress acts as the force source for the plastic floor heave.

With regard to the mechanism of electromagnetic radiation (EMR) excited by deformation and failure of coal and rock, the present study employed the optical microscope, digital microhardness tester and atomic force microscopy (AFM) to measure surface morphology, surface microhardness and electro-mechanical characteristics, including elastic modulus and surface potential of coal. The results show that micro-mineral composition and micro-mechanical properties of coal are clearly heterogeneous. The elastic modulus values measured are 62.3 MPa–4.0 GPa and the surface potential values tested are 21.2–166.2 mV. The proportion distributions of the two parameters mentioned follow the normal distribution, which indicates the electro-mechanical characteristics of coal are clearly inhomogeneous at the micro- and nanoscales. Finally, the effects of the inhomogeneous elastic modulus and surface potential on the EMR from the microscopic perspective were analyzed. In this experiment, the change of the micro-elastic modulus and the existence of the surface potential on the coal surface were directly observed. The findings reveal the mechanism of EMR induced by deformation and failure of coal and rock.

In this study, we established a dynamic ejection coal burst model for a coalmine roadway subject to stress, and held that the stress concentration zone at the roadway side is the direct energy source of this ejection. The formation and development of such burst undergoes three stages: (1) instability and propagation of the cracks in the stress concentration zone, (2) emerging of a layered energy storage structure in the zone, and (3) ejection of coal mass or coal burst due to instability. Moreover, we figured out the initial strength of periodic cracks is parallel to the maximal dominant stress direction in the stress concentration zone and derived from the damage strain energy within the finite area of the zone based on the Griffith energy theory. In addition, we analyzed the formation process of the layered energy storage structure in the zone, simplified it as a simply supported restraint sheet, and calculated the minimum critical load and the internally accumulated elastic energy at the instable state. Furthermore, we established a criterion for occurrence of the coal burst based on the variational principle, and analyzed the coal mass ejection due to instability and coal burst induced by different intensity disturbances. At last, with the stratum conditions of Junde Coalmine as the model prototype, we numerically simulated the load displacement distribution of the stress concentration zone ahead of the working face disturbed by the main roof-fracture-induced dynamic load during the mining process as well as their varying characteristics, and qualitatively verified the above model. Keywords: Coal and rock burst, Evolution model, Dynamic ejection, Stress concentration, Layered energy storage structure

To achieve the qualitative and quantitative damage expression, coal samples within original cracks were selected to conduct uniaxial compressive loading experiments. During this process, acoustic emission signals were collected by AEwin Test for Express-8.0 and cracks evolution were captured by video camera. The results showed that the larger the initial damage, the lower the uniaxial compressive strength and elastic modulus of coal samples. When coal samples were subjected to uniaxial compression, the primary cracks closed firstly. Then friction phenomenon might generate due to sliding along the cracks surface and the deflection might occur at the center of cracks. Finally, original cracks expanded and new cracks formed and propagated to cause sample fracture, all which leaded to acoustic emission events. AE counts and accumulated counts changed with time, which corresponded well with stress–strain. Therefore, the value of AE counts and the trend of accumulated counts qualitatively explained the damage evolution laws of loaded coal. Further, based on the damage theory of acoustic emission counts, the quantitative damage variable was proposed and calculated. What’s more, the force analysis near the cracks surface at the initial loading process was explained and the cracks dynamic evolution during the whole compressive loading process was discussed. It was helpful to understand the damage evolution mechanism of coal samples.

It is vital to understand the electromagnetic radiation’s time-frequency characteristics in the process of coal and rock failure with different joint angles in order to reveal the generation mechanism of the electromagnetic radiation (EMR) and improve the accuracy of EMR early warning. We studied the time-frequency characteristics of EMR signals of coal samples with different joint angles. The study finds that, (1) with the increase of joint angle, the failure time and peak load of samples decrease first and increase later, and the postpeak failure time decreases gradually. The EMR counts’ peak value showed a slow rise, a sharp rise, and a slow rise in the three intervals of α = 0° to 45°, 45° to 60°, and 60° to 90°, respectively. The accumulated EMR counts showed a steady upward trend. The duration of the EMR waveform, the dominant frequency of the EMR, and the peak number of the frequency spectrum of coal samples are on the rise. (2) As the joint angle increases, the samples’ failure mode changes from the stage fracture dominated by tension cracks to the rapid fracture with the coexistence of shear and tension cracks and finally to the burst fracture which produces a large number of fragments. This is also the main reason for the difference of the EMR generation mechanism and the signal of samples with different joint angles. (3) According to the experimental results, we established the modified formulas for calculating the EMR threshold value and deviation of coal and rock with joints under different stress environments and revealed that the longer the EMR waveform duration, the higher the dominant frequency, and the more the number of spectrum peaks, the greater the burst risk of coal and rock.

This work extends research on the mechanism of electromagnetic radiation (EMR) induced by coal or rock fractures to the category of microscopic dynamic experimental research. A custom-made three-point bending test system and atomic force microscope (AFM) were integrated to obtain the microdynamic loading test system. The notched coal samples were prepared specially. The dynamic propagation of new microcracks in coal samples was measured, and the propagation velocity was calculated. The morphology and electro-mechanical characteristics of new microcracks were tested. More importantly, the causes of the changes in the electro-mechanical characteristics before and after fracture were analyzed, and the effects of these changes on the EMR were discussed. The results showed that the average propagation velocities during the same time interval are 9.5 μm/s, 12.1 μm/s, and 16.2 μm/s. The elastic modulus of the material at the microcrack edge is generally smaller than that of the material in other locations, while the adhesion and deformation are larger. Moreover, the closer the material is to the microcrack, the higher its surface potential. The electrons generated at the microcrack edge and emitted into the atmosphere, which made the greater potentials of the microcrack edge. Many electrons with different velocities and directions migrate in similar parallel-plate capacitors, which are formed by the relative microscale surface of the coal microcrack tip and have different field strengths, resulting in EMR with complex frequencies and different intensities. This study provides a micro-dynamic experimental basis for research on the electromagnetic radiation mechanism.

The steeply inclined and extremely thick coal seams (SIETCS) under the condition of gob filling frequently suffer from the occurrence of rockbursts. Figuring out the mechanisms of rockbursts under this condition for taking targeted measures to mitigate rockburst hazards in SIETCS is of great significance. Using the typical SIETCS with an average dip angle of 87&deg, at Wudong Coal Mine (WCM) as a case study, a mechanical model and elastic deformation energy (EDE) function of a &ldquo, steeply inclined suspended roof structure&rdquo, was developed, and the influence factors were analyzed by theoretical analysis. Simultaneously, the rockburst risk assessment was carried out based on the theory of a rockburst start-up. The pressure relief measures are optimized by comparing the pressure relief effects of three kinds of destress blasting schemes. The results indicate that the damage characteristics of rockburst are mainly floor heave, the sidewall&rsquo, s inward deformation and roof subsidence. The damage degree of headentry on the roof side is more severe than that of tailentry, and the resultant impacts showed the directionality from the roof side to the coal side. The steeply inclined and suspended roof breakage is one of the main causes for the occurrence of rockbursts. The EDE of the roof increases with an increasing dip angle of the coal seam from 0&deg, to 72.6&deg, and then decreases as the dip angle increases. Furthermore, that increase is accompanied by the decrease of the lateral pressure coefficient and the supporting force coefficient. The EDE stored in the roof is sufficient to cause roof breakage and induce rockburst after the complete roof exceeds a certain length. The mechanism of rockburst in SIETCS for fully mechanized top-coal caving mining under gob filling conditions was proposed, i.e., &ldquo, high compressive stress concentration plus breakage of the suspended roof-induced stress&rdquo, rockburst, and this is further verified by ground destruction, microseismic (MS) monitoring and numerical modeling. The results also indicate that alternate deep and shallow hole-blasting modes are more suitable for pressure relief in SIETCS.

Aiming at problem of low efficacy of early warning of rock burst in coal mine, a multisystem and multiparameter integrated early warning method based on genetic algorithm (GA) is proposed. In this method, firstly, the temporal-spatial-intensity information of energy incubation process of rock burst is deeply mined, and the multidimensional precursory characteristic parameter system of rock burst is constructed. Secondly, the genetic algorithm is used to train the historical monitoring data to obtain the optimal critical value and fitness value of each precursory characteristic parameter, and then the early warning index WC of each monitoring system is calculated. Finally, the integrated rock burst early warning index IC is obtained by synthesizing the early warning index WC of each system. The value of IC corresponds to the specific rock burst risk level of the mine. This method is applied to Wudong coal mine in Xinjiang, China. Based on the actual situation of the mine, a multidimensional precursory characteristic parameter system of rock burst is constructed, which includes energy deviation (DE), frequency ratio (Fr), frequency deviation (DF), degree of dispersion (DS), and total high value of energy deviation (DH). After analyzing the rock burst danger status and risk level in the monitoring area, the early warning capability of this method is found to reach 0.896. Combining with the specific prevention and control measures corresponding to different rock burst risk levels, it can provide effective guidance for the field work.

In recent years, rockbursts have occurred frequently during the mining of thick coal seams in China. Use of the top-coal caving or slicing mining method to extract these thick seams may result in distinct geomechanical responses in the strata and, in turn, the pattern of rockburst occurrence around longwall layouts. To establish a thorough understanding of which method (caving or slicing) is better when it comes to preventing rockbursts during the extraction process, a suite of in situ rockburst measurements was conducted. Six typical rockburst-prone collieries were monitored during which a total of 110 rockburst events occurred. Numerical modelling was used to help interpret the observations. Here, we focus on the analysis of these field observations and the numerical simulations employed to develop a conceptual model for rockburst occurrence during caving mining of thick coal seams. We find that caving mining has a certain rockburst-reducing effect in that the method significantly decreases, or even avoids, the occurrence of rockbursts at coalfaces. Moreover, it reduces the scope of the damage likely to be incurred and the severity and frequency of rockbursting. According to the conceptual model, the rockburst-prone area during caving mining is generally the roadway section located a certain distance ahead of the coalface. This distance, which is roughly 10–54 m, is consistent with the rockburst damage observed on site (mostly 10–50 m ahead of the coalface). This rockburst pattern arises because caving mining results in reduced stress concentration, less bottom coal being retained, and wider-ranging fracture zones around the mine openings, especially ahead of the coalface. This makes the rock surrounding the mine openings less likely to accumulate high levels of elastic energy that need releasing and hence it is more difficult to induce rockbursting. Therefore, it is recommended that the top-coal caving method should be the preferred method of extraction when mining coal seams of a certain thickness.

By comparing the overburden structure characteristics and the distribution of stresses around roadways and coalfaces in slice mining and top-coal caving mining in thick coal seams , this study analysed the effects of the two mining methods on rockburst prevention. Furthermore, by using FLAC3D numerical simulation, this research studied the distribution of surrounding rock stress in the first mining panels, subsequent panels, solid coal roadways, and gob-side roadways and the influence of parameters including mining height, bottom coal, and coal seam thickness on stresses in the surrounding rocks. On this basis, the effects of load shedding and rockburst reduction of top-coal caving mining of thick coal seams were summarised and verified through field investigation. The results show that compared with slice mining, overburden structures in top-coal caving mining of thick coal seams weakened the stress concentration in surrounding rocks, resulting in lower peak values but wider ranges of advanced abutment stress and side abutment stress in panels. The point of peak stress was observed deeper into the coal masses. With the increase of mining height and the decrease of bottom coal thickness, the stress concentration around roadways and coalfaces decreased rapidly and then tended to be stable. Therefore, top-coal caving mining can reduce the stress concentration around roadways and coalfaces to decrease rockburst risk. While mining thick coal seams, top-coal caving mining needs to be conducted preferentially over a reasonable range of mining heights. Field practice in Xing’an and Junde mines revealed that the top-coal caving mining induced a lower rockburst frequency, over a smaller range and with lower intensity, which validated the effects of load-shedding and rockburst reduction of the proposed mining method.

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional (PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle θ between the bedding planes and load direction. With θ increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when θ was 30° or 45°. Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with θ of 30° or 45° reduced the specimens’ ability of storing strain energy to the lowest with fewer cracks observed after failure. Keywords: Static–dynamic coupled loads, SHPB, Coal bedding angle, Strain energy, PFC2D

This paper presents an electromagnetic radiation-based method to qualitatively assess mine-induced stress field at the longwall face. We first analyze the correlation between electromagnetic (EM) signals and stress, and then measure the signals and drilling bits in both the strike and dip directions at the 11702 working face of Nuodong Coal Mine, China, which indirectly verifies this method. Results show that there is a positive correlation between EM intensity and stress. In the same coal seam, the frequency of EM signals is inversely proportional to the extended size of the cracks inside the coal rock, and the dominant frequency (DF) of the EM signal is negatively related to external stress. Test results in Nuodong Coal Mine show that the EM intensity and DF can well reflect a stress relief zone, concentration zone and original zone. In addition, through field test and theoretical calculation, we can ascertain that the crack propagation length is from several centimeters to greater than 20 cm. The stress magnitude inside the coal rock can be qualitatively evaluated by using the correlation of the EM signal intensity, frequency and stress.

In order to further explore the mechanism of electromagnetic radiation of coal and rock during loading, the change characteristics of electrical parameters including surface potential and charge density of the four types of rocks under dynamic and static conditions were assessed and tested using Atomic Force Microscope (AFM) and Micro-loading device. The results show that under static conditions, the micro-surface potential of the four rocks ranges between −922 mV and 235 mV, and the micro-surface potential has a good correlation with the charge density of the same type rock; under dynamic conditions, the micro-surface potential of the rock increases constantly with the loading, the range of the average value of the electric potential is −0.366∼1.188 V, and the micro-surface potential is positively correlated with the load, which has an obvious force-electric coupling effect. This work reveals the electrical characteristics of rock micro-surface under dynamic and static loading conditions, which may provide important experimental basis for further revealing the microscopic mechanism of electromagnetic radiation and improving theoretical system of electromagnetic radiation.

Coal rock friction generally exists in various geological movements, and it is of great significance to effectively monitor the friction process. In this paper, the commonly used methods of coal rock friction are systematically summarized, and the double shear friction experimental method suitable for coal friction electromagnetic radiation monitoring is preferentially selected. A coal friction device with controllable lateral pressure was independently developed, coal friction experiments were carried out under different lateral pressure, and the time-frequency evolution law and generation mechanism of electromagnetic radiation in coal friction were studied. The results show that coal friction can generate abundant EMR signals. With increasing coal friction lateral pressure, the EMR signal develops from sparse to abundant, and the signal energy, amplitude, and dominant frequency gradually increase. The EMR signal of the coal friction process shows clear stage characteristics. At the stable sliding stage, the EMR signal is weak and energy is low. At the stick slip stage, the EMR signal is generated intermittently along with the load drop cycle, with more signals and strong intensity. The main mechanisms of coal friction EMR are the frictional slip electrification of the micro-convex body on the coal surface, charge separation, and the variable-speed movement of the charged particles formed by crack propagation of the micro-convex body. These results clarify the mechanical behavior of coal friction sliding instability and the time-frequency evolution law of the EMR of coal friction, which further improves the accuracy of EMR monitoring and early warning of coal rock dynamic disasters.

Understanding the micro and nano-scale surface deformation and mechanical properties of rock under load possess enormous significance for underground engineering research and provides strong basis for comprehending rock failure as well. According to the documented research, the in-situ observation of micro-surface under dynamic load has not been yet reported. With this motive, a novel approach is presented in this work that takes advantages of combined Atomic Force Microscope (AFM) and customized micro-loading device for in-situ characterization of the the micro-surface topography and elastic modulus of rocks under different load strength. The in-situ comparison of micro-surface properties is carried out using interactive tools of AFM image post-processing software including crop and split, and section analysis. Taking the typical observation results of igneous rock and shale as an example, the results show that the micro-surface topography undulations of rock can reach up to tens of nanometers. Although no apparent fracture occurred, the local fluctuation of the rock samples’ micro-surface changed with the increasing load strength at nanometer level, and in the measurement area of 5 × 5 μm2, the topographies of different pixel points are various, showing significant local difference. With the increasing load strength, the elastic modulus distribution of the rock’s micro-surface shows heterogenity, and the local elastic modulus also increases or decreases, while the variation difference at different pixel points reaches hundreds of MPa. Additionally, the macroscopic fracture characteristics of rock under load, especially the non-uniform crack propagation and its mechanism are discussed. The analysis indicates that the heterogeneous distribution of the rock’s micro-surface elastic modulus and its local complex change with load are accounting for the complexity of the macroscopic crack path and the numerous crack branches. This study provides a novel insight into micro-surface behavior in rock and presents a new method for the investigation of the fracture mechanism of rock.

Rockburst is a serious hazard in underground engineering, and accurate prediction of rockburst risk is challenging. To construct an intelligent prediction model of rockburst risk with interpretability and high accuracy, three binary scorecards predicting different risk levels of rockburst were constructed using ChiMerge, evidence weight theory, and the logistic regression algorithm. An intelligent rockburst prediction model based on scorecard methodology (IRPSC) was obtained by integrating the three scorecards. The effects of hazard sample category weights on the missed alarm rate, false alarm rate, and accuracy of the IRPSC were analyzed. Results show that the accuracy, false alarm rate, and missed alarm rate of the IRPSC for rockburst prediction in riverside hydropower stations are 75%, 12.5%, and 12.5%, respectively. Setting higher hazard sample category weights can reduce the missed alarm rate of IRPSC, but it will lead to a higher false alarm rate. The IRPSC can adaptively adjust the threshold and weight value of the indicator and convert the abstract machine learning model into a tabular form, which overcomes the commonly black box problems of machine learning model, as well as is of great significance to the application of machine learning in rockburst risk prediction.

The development of reliable early rockburst warning models for underground mines is a challenging task considering the complex nature of rockburst phenomena. In this paper, a real-time, integrated multi-system, early rockburst warning model is developed to achieve the quantitative prediction of the rockburst probabilities at a specific time. The model input parameters are data derived from microseismic (MS) and acoustic emission (AE) monitoring systems. The early warning model is based on fuzzy comprehensive evaluation method (FCEM), confusion matrix and maximum membership degree principle. These tools integrate the advantages of both multi-system and multi-parameter into one unified model. During the early warning procedure, six early warning indices representing temporal, spatial and energy parameters are rationalized. Next, the weight of each index is determined from confusion matrix leading to a score value. Real-time early warning results can then be determined from the maximum membership degree principle. The results show that the proposed integrated MS-AE early warning model has the advantage of combining multiple systems and indices, and it has higher prediction accuracy than individual systems. The early warning model is successfully demonstrated with a case study from the Wudong Coal Mine in China. The proposed model improves the rockburst early warning efficiency and provides a solid foundation for ensuring the safety of personnel and equipment in underground mining.

Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels. Keywords: Mine tunnel, Turbulence, Airflow distribution, Three-center arch, Average velocity

In order to improve the monitoring and prediction of coal and gas outburst, this paper proposes a new method for dynamic regional prediction of coal and gas outburst using microseismic (MS) monitoring. The theoretical basis of this method is presented. An index evaluation system was established and applied, based on which field tests were carried out in a coal mine. The results show that seismic monitoring with frequency and energy indexes can obtain good results for mining disturbance intensity monitoring and geological structure detection; the regional stress distribution detected by seismic wave tomography is consistent with the theoretical stress field, making its use of great significance for optimizing coal and gas outburst drilling parameters and improving overall tunneling efficiency. This approach overcomes the limitations of traditional methods in the temporal and spatial dimensions and realizes dynamic and continuous monitoring of coal and gas outburst-prone areas.

Rock burst is one of the major geological hazards in coal mines and is difficult to prevent. Faced with this problem, the low-frequency electromagnetic radiation (EMR) test experiments of coal and rock were conducted to explore the characteristics of low-frequency EMR (1 kHz) signals induced form fractures. The relation between EMR signals and paroxysmal fractures was analyzed theoretically. Time-series extraction method was put forward to represent coal and rock paroxysmal fractures. The research results showed that deformation and fracture of coal and rock is caused by the accumulation of paroxysmal and discrete fractures in the samples. The time series obtained by moving average method shows rather good correlation with interior coal rock fractures, which has more obvious precursory characteristics of coal rock instability and dynamic disasters. When the coal rocks are damaged under uniaxial compression, low-frequency EMR (1 kHz) signals are more sensitive to local fracture with more abundant precursor information than high-frequency EMR (500 kHz) signals. The paroxysmal and discrete low-frequency EMR (1 kHz) signal is quite sensitive to rock burst, and when the signals representing coal rock fractures show an increasing trend and the high signals last for some time, it can be regarded as the precursor of rock burst disaster in coal mine. The separation technology of EMR representing coal rock fractures provided the key scientific basis for the field monitoring and forewarning of EMR technology, and a new method to identify the precursor of dynamic disasters of coal and rock.