Search

Abstract To explore the multiparameter precursor characteristics of pre- and post-coal burst. Based on a coal burst of LW 1305 in the Zhaolou Coal Mine, an early warning method combining stress‒strain curve and microseismic multiparameter is proposed. The research results show that coal burst was induced by the intrinsic static high-stress concentration and the strong external impact loading generated by fracturing of the key stratum. The precursors mainly characterize the enhancement trend of the S value, the sudden and sharp increase in the A(t) value, the continuous and abnormal decrease in the b value, the increasing absolute value of Z sharply and larger than 2, the continuous and abnormal decrease in the Qt value, and the dominant frequency moving to the low-frequency band. Essentially, many micro-fissures inside the key stratum initiated, converged and connected to form macro-fractures, which was verified by the attenuation rate of the K value. Considering the time-varying effect of the overlying stratum movement, the curves of the six parameters agree well with those of stress vs. strain, which indicates that it is reasonable to take the observed zone as a whole system to investigate the variation in the multiple parameters and fracturing of the key stratum. The research results can be applied to the monitoring, early warning and control of coal burst so that effective safety measures can be taken in real time.

The small-scale roadway model is often used in the fine simulation of mining engineering. The determination of the structure and load conditions of the model has an important influence on the accuracy of the simulation. In this paper, a large-scale stratum model and a small-scale roadway model are established by using finite element method. The optimal loading mode of the roadway model and its applicability under different roof-sidewall stiffness ratios are studied. The simulation accuracy of the roadway model is quantitatively evaluated by comparing the distribution laws of stress field and strain field with those of the stratum models. Under the same roof-sidewall stiffness ratio, the similarity between the simulation results of the roadway model and the stratum model under displacement load is much higher than that under stress load. Under the same load mode, the stress and strain similarity between the stratum model and roadway model increases with the increase of the roof-sidewall stiffness ratio. Furtherly, the simulation application of the roadway drilling pressure relief is carried out. Compared with the large-scale stratum model with small-size elements, the small-scale roadway model under displacement load also shows obvious stress transfer after drilling pressure relief, while it has faster computational efficiency. Finally, a small-scale roadway model simulation method suitable for surrounding rock disaster occurrence mechanism and control is proposed. [ABSTRACT FROM AUTHOR]

Due to high-intensity mining and complex geological conditions, frequent occurrence of rock burst disasters in deep coal mines in China is posing serious threats to mine safety and efficiency. The insufficient locating accuracy of the seismic monitoring system in burst-prone coal mines is still presented, which leads to difficulties in accurately identifying and controlling coal burst hazards. To precisely characterize spatial evolution of seismic activities and reduce the impact of location error on the seismic pre-warning, this paper used the current seismic networks in burst-prone coal mines to conduct forward modeling experiments to explore the distribution characteristics of source location error vectors in the mining field. A new method for characterizing seismic fracture connectivity that considers location accuracy impacts was proposed and applied for coal burst pre-warning in a longwall face. The results show that significant vectorial differences of seismic source location accuracy at different area of the mining field is a key factor in false identifying coal burst risks. The proposed Fracture-connectivity-probability Index (\begin{document}$ F{_{{\mathrm{sum}}}} $\end{document}) characterizes the rupture scale by using the near-field radius that relates to the seismic energy level, which considers the locating error impacts on fracture connectivity between seismic sources at different distances. \begin{document}$ F{_{{\mathrm{sum}}}} $\end{document} can restore the distribution law of the fracture extension and connectivity probabilities of the coal-rock mass in the greatest extent, and it also corresponds well to the coal burst risks. \begin{document}$ F{_{{\mathrm{sum}}}} $\end{document} can balance forecast accuracy and recall rate and have better correlation with coal burst, which can be an ideal indicator for periodical coal burst risk assessment. The outcome of this research can provide references for evaluating the monitoring capability of seismic networks and improving the ability and efficiency of coal burst pre-warning and prevention.

AbstractExtra-thick key strata (ETKS) are a key factor causing coal bursts. In this study, field monitoring, physical and numerical modelling, and theoretical analysis were comprehensively adopted to investigate the effect of ETKS on the static and dynamic stress and its impact on coal bursts. Firstly, the coal bursts and the stability of ETKS were investigated. The roof strata structure and the mining-induced stress in a large scale panel under ETKS were analyzed. Then, the coal burst mechanism under ETKS is discussed. The results show that when the panel reaches the 4th and 5th longwall faces, the inferior ETKS and the main ETKS break, respectively, and large-scale cantilever-articulated structures involving the ETKS are formed. This moment, the overburden load is transferred downwards massively, and the coal seam becomes overstressed and accumulates massive elastic energy. Meanwhile, the collaborative collapse of multiple strata in the large cantilever-articulated structures causes the sudden release of elastic energy and high-energy seismicity, which exerts strong dynamic disturbances on the overstressed coal mass and leads to coal burst. Finally, strategies for coal burst control under ETKS including deep-hole pre-splitting blasting and panel size optimization are proposed and validated.

In this study, triaxial compression tests were conducted on coal to better understand the mechanism of coal burst disasters in deep coal mining. The mechanical properties, energy evolution and brittleness of coal under various true triaxial stress states were investigated. The evolution equation of the dissipated energy based on the logistic function was constructed, and the dissipated energy was defined as the damage factor D to determine the three-dimensional damage constitutive model of coal considering the residual strength. The findings indicate that, in the presence of true triaxial stress, the coal's peak strength, residual strength, and elastic modulus increase as confining pressure rises while the absolute post-peak modulus drops. When confining pressure is low, coal failure manifests as brittle tensile–shear composite fracture; as confining pressure rises, the brittle characteristics gradually weaken, and shear fracture takes over as the primary failure mechanism. The brittleness index, which entirely considers the pre-peak and post-peak behaviors, is a better indication of the brittleness of coal under true triaxial conditions than other indices. The established damage constitutive model can adequately predict the coal's strength and better characterize the coal's complete stress–strain behavior, especially for high brittle coal. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

The development of stiffness theory is constrained by its contradiction with engineering experience. Several easily overlooked details of stiffness theory were clarified, and a qualitative evaluation formula for the risk of coal burst was provided. Then a novel structure factor called uneven stiffness coal seam structure (USCS), which consists of high stiffness zone (HSZ), low stiffness zone (LSZ), and contiguous roof and floor, was proposed. Many areas prone to coal bursts, such as thinning zones, bifurcating areas, magmatic intrusion areas, and remnant pillar affected areas of coal seam, are the HSZs of USCSs. Comparative analysis of the uneven stiffness coal seam under different roof conditions and examination of the simplified trisection model of the USCS were conducted. Then 6 groups of 14 simplified 2D models using COMSOL5.2 was constructed based on controlled variable method to simulate different responses of the USCS with varying parameters under same working conditions. The results demonstrate the following: (1) coal bursts occur only when both the failure criterion and the stiffness criterion are simultaneously satisfied, the risk of coal burst (rCB) is the product of the risk of failure (rF) and the risk of instability (rI). (2) The pressure concentration function of USCS facilitates stress concentration from LSZ to HSZ, thus raising the rF in HSZ. The stiffness reduction function of USCS reduces the local mine stiffness (LMS) of the HSZ, allowing the system to meet the stiffness criterion even with a hard roof, thereby raising the rI in HSZ and reconciling the contrast between stiffness theory and engineering experience. Failures within HSZ of the USCS enables the roof strata to release bending deformation energy without roof breakage. (3) The normal stress of HSZ is positively correlates with the value of ERHRKHSL/KLSH; The LMS of the HSZ is positively correlated with the value of ERKL/KHHRSLSH. The USCS boasts significant advantages in integrating and harmonizing various existing theories and explaining multiple specific types of coal bursts. By applying relevant USCS findings, new explanations can be provided for engineering phenomena such as the time-delayed coal bursts, the inefficient pressure relief in ultra thick coal seams, and the "microseism deficiency" observed prior to certain coal bursts. [ABSTRACT FROM AUTHOR]

This study explores the causes of coal bursts in the Xinzhou Kiln Mine, identifying key factors such as residual pillars, hard coal seams and/or roofs, stress concentration due to complex geological structures, and the stress distribution characteristics of the primary rock. A significant finding is that hydraulic cutting not only diminishes and redistributes the stress concentration region inside the coal seam but also mitigates the burst potential of the coal-rock mass, fundamentally reducing the likelihood of coal bursts. By taking Face No. 8937 in Xinzhou Kiln Mine as the test object, a coal burst prevention test was performed using hydraulic cutting. In combination with theoretical analysis and numerical simulation, the mechanism of hydraulic cutting for preventing coal burst was discussed, and reasonable cutting parameters were established. Onsite monitoring revealed that hydraulic cutting disrupts the integrity of the coal-rock mass, releases internal stress, and increases its water content, thereby weakening its burst tendency. Additionally, the deformation and fracturing of the cutting slots and the closure of boreholes shifted the stress concentration from the coal seam to deeper areas and to the two ribs. Post-cutting observations showed a significant reduction in both the frequency and impact energy of coal bursts; there was also a noticeable increase in the convergence of the roadway in the cutting area compared to non-cutting areas. Furthermore, displacement of the roof and floor increased by 78.9 % and that of the two ribs increased by 47.4 % after cutting, preventing the coal-rock mass from accumulating high stress. In conclusion, hydraulic cutting is a promising method for effectively preventing coal bursts and enhancing the safety of mining operations.

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.

Abstract The assessment of Coal burst risk (CBR) is the premise of bump disaster prevention and control. It is the implementation criterion to guide various rock burst prevention and control measures. The existing static prediction and evaluation methods for CBR cannot be effectively combined with the results of underground dynamic monitoring. This study proposed a mining-induced seismicity information quantification method based on the fractal theory. Deep learning methods were used to construct a deep learning framework of coal burst risk (DLFR) based on the fractal dimension of microseismic information. Gray correlation analysis (GRA), information gain ratio (IGR), and Pearson correlation coefficient are used to screen and compare factors. Statistical evaluation indicators such as macro-F1, accuracy rate, and fitness curve were used to evaluate model performance. Taking the Gaojiapu coal mine as a case study, the performance of deep learning models such as BP Neural Network (BP), Support Vector Machine (SVM) and its optimized model based on particle swarm optimization (PSO) algorithm under this framework is discussed. The research results' reliability and validity are verified by comparing the predicted results with the actual results. The research results show that the prediction results of CBR in DLFR are consistent with the actual results, and the model is reliable and effective. The mining-induced seismicity quantification can solve the problem of insufficient training samples for the CBR. With this, different pressure relief measures can be formulated based on the results of the CBR predictions to achieve "graded" precise prevention and control.

Under the background of coal mine intelligent construction, how to efficiently extract adequate information from the massive monitoring data of coal burst and improve the accuracy of prediction and warning is the focus and difficulty of future research. Aiming to solve the challenges of the poor generalization ability of current physical model-based coal burst prediction methods and insufficient feature mining of massive data, combined with deep learning technology, a time series coal burst prediction method driven by the fusion of physical model and data feature was initially established. In this paper, taking a strong coal burst risk longwall face in Binchang Mining area, Shaanxi Province as the background, the variation characteristics of physical indicators before several large energy events are analyzed, and the shortcomings of coal burst risk prediction indicators driven only by physical models are statistically analyzed. The coal burst time domain prediction method driven by the fusion of physical model and data feature is proposed. The prediction model includes three modules: data preprocessing, feature extraction, and early warning model construction−the data preprocessing processes the original microseismic monitoring data into precursor pattern sequence within a specific time window. Feature extraction based on a physical model mainly includes the characteristics of explicit and implicit data feature extraction based on convolution neural network. The explicit and implicit characteristics of the depth of the fusion method was put forward based on attention mechanism, and through the whole connection network forecast model classification, the impact of different risk levels of large energy events. The model test results show that the prediction F1 score can reach 0.956, 0.950, and 0.854, respectively, when the prediction time is one day, two days, and three days in the future. The site can choose the prediction time according to the demand. In engineering application, the model can accurately predict large energy events, and the error analysis results show that the prediction accuracy of the model is high, which can meet the needs of the site.

Rock mass dynamics disasters caused by excavations and mining occur frequently in deep mines. In order to establish a theoretical system and control technologies for such disasters, we first classify and define dynamic disasters, such as rock bursts, coal bursts, mine pressure bumps, and mine earthquakes. According to the occurrence mechanism of different types of dynamic disasters, we establish a compensation control theory based on excavation and mining effects. On the basis, we propose three key technologies: high prestress compensation technology for the roadway, pressure relief technology using directional roof cutting, and the goaf filling technology using broken rock dilation. These three technologies constitute the compensation control method for dynamic disasters in deep mines. Finally, this method was successfully applied in a deep coal mine with high stress, with monitored results suggesting its rationality. This work provides a new concept and control method for the prevention of rock dynamic disasters in deep mines.

Abstract Water injection, as a widely used technique to prevent coal burst, can restrain the fractured coal seam and released the energy storage. In this study, laboratory tests were firstly carried out on standard coal specimens with five different water contents (i.e., 0%, 0.6%, 1.08%, 1.5%, 2.0%, and 2.3%). The failure mode, fragment size, and energy distribution characteristics of coal specimens were investigated. Experimental results show that strength, elastic strain energy, dissipated energy, brittleness index, as well as impact energy index decrease with increasing water content. Besides, the failure mode transitions gradually from splitting ejection to tensile-shear mixed failure mode as water content increases, and average fragment size shows positively related to water content. Moreover, scanning electron microscope tests results indicate that water in coal sample mainly causes the mineral softening and defects increase. Furthermore, a numerical model containing roadway excavation was established considering the water on coal burst prevention. Modelling results revealed that water injection can reduce degree of coal burst and ejection velocity of coal blocks, while it will raise up the depth of crack zone and surface displacement of roadway. Combined with laboratory tests and numerical results, the micro mechanism, energy mechanism, and engineering significance of water injection on coal burst prevention were finally analyzed.

The frequent occurrence of coal burst in coal mines is closely related to the destabilization of complex geological formations, and the fault as a typical geological structure is an important factor in inducing dynamic coal burst disaster. In this study, the distribution function solutions of displacement and energy fields characterizing fault sliding were derived. Under the engineering background of geological structure of the Yima mine area in Henan Province and the mining face 21221 of the Qianqiu coal mine, a physical model to simulate the mining process and fault sliding of the mining face was built. The multi-parameter evolution law of displacement, energy, and temperature of the overburden rock strata and fault area were monitored, and the mutation effect of fault and overburden rock strata instability was investigated. In addition, the mechanical mechanism of the association and coupling of overburden rock strata movement and fault slip instability caused by mining disturbance was discussed. The results show that the frequency of extreme value points of stress, displacement, and energy parameters on the fault surface under the mining disturbance presents a dense to sparse distribution from top to bottom along the vertical direction of the fault. In the meantime, the upper part of the fault surface in a non-stable state is more susceptible to the influence of mining than the lower part, which is the main power source of fault sliding. Fault sliding is a top-to-bottom, local-to-whole, low-energy followed by high-energy, gradually accelerated and discontinuous dynamic destabilization process, which is accompanied by three strain energy states of low-energy stability, gradual accumulation, and high-energy activation. The maximum strain energy increment appears in the upper part of the fault surface, and the massive release of strain energy will accelerate the top-to-bottom destabilization of the fault slip. During the sliding process of the fault surface, the temperature also shows the characteristics of stepwise increase, which is manifested as the constant temperature stage during the small disturbance, the local rising stage caused by the stress accumulation, and the global temperature surge stage caused by the sliding instability. The nonlinear and discontinuous dynamic instability of the fault is closely related to the movement and collapse of the overlying rock layer on the working face. The mutation effect of the coupled instability of the fault and overburden rock strata was studied based on the correlated coupling response between the movement of overburden rock strata and the fault sliding during the mining disturbance. It is manifested by the sudden increase of the overburden rock strata pressure near the fault, the drastic change of the stress on the fault surface, the accelerated change of the fault displacement and its development to the lower part, the large and frequent fluctuation of the strain energy, and the order increment of the temperature field. The studies indicate that the overburden rock strata collapse imposes impact loads on the unsteady slip of the fault, and the fault serious slip instability caused by the strain energy sudden release will also bring a secondary violent impact to the deformed and damaged overburden rock strata and cause a large area collapse. The resulting unloading effect provides additional space for the fault to move into the region, which further accelerates the slip instability of fault and the collapse of overburden rock strata, and easily induces coal burst disaster.

Aiming at the problem that the traditional discrimination method of rock burst generation lacks the consideration of the whole disaster process and has some defects, taking the decomposition of the physical process of coal mine rock burst generation as the starting point, the calculation formula and application of the discrimination index of coal mine rock burst generation based on the decomposition of physical process are investigated by using the methods of theoretical analysis, numerical simulation, mechanical derivation and engineering verification. The results show that the spatial sequence in the physical process of rock burst is the limit equilibrium zone of mining surrounding rock-near-field elastic and plastic zone of mining surrounding rock-mining activity space. The corresponding time series are burst initiation stage, burst energy transmission stage and burst ground pressure manifestation stage. To complete the whole physical process of rock burst, two mechanical conditions must be met at the same time: impact start-up and overcoming impedance. The dynamic and static load type and high static load superposition type rock burst start-up mechanical models and rock burst impedance overcoming mechanical models are established respectively. The starting energy criterion formula of rock burst and the apparent energy criterion formula of rock burst are obtained. Based on the above two formulas, the calculation formula of rock burst occurrence discrimination index has been derived considering both dynamic load sources and static load sources, and taking into account that the mechanical conditions of rock burst initiation and rock burst appearance are satisfied. According to the discriminant index formula, it is obtained that the possibility of rock burst is directly proportional to the sum of static and dynamic loads of coal and rock mass, and inversely proportional to the impedance energy of support and surrounding rock. The structural mechanics model of roadway load-reduction impedance-increase coupling anti-burst engineering based on the occurrence discrimination index of rock burst is established and applied in engineering. The practice shows that the purpose of preventing rock burst is achieved.

Under the background of the rapid development of intelligent coal burst monitoring technology, how to use massive seismic monitoring information to investigate source rupture and apply it to the prediction, early warning, or prevention of coal burst is the focus and difficulty of future research. To solve the problems of insufficient investigation of seismic clustering fracture mechanism aggregation law and overcome the difficulty of direct application of seismic source mechanism inversion technology to the prediction and early warning of coal burst, the theoretical analysis and numerical simulation methods are used to establish a prediction method of coal burst risk based on seismic source mechanism and location error calibration. Taking the 2215 working face with frequent high magnitude seismic events in a coal burst mine in Inner Mongolia as an example, this paper summarizes the characteristics of the limited number of seismic waves, large noise impact, and high inversion efficiency. Also, it compares and analyzes the characteristics, advantages, and disadvantages of different moment tensor inversion methods, and establishes that the hybrid moment tensor inversion method is more suitable for coal mine application scenarios. The statistical results of the rupture mechanism of high magnitude events in the 2215 working face show that the main inducing events of roof rupture are a tensile shear failure and compressive shear failure. The shear component statistics of seismic events before the occurrence of high magnitude events show that the proportion is not more than 40%. The occurrence statistics of source rupture surface show that the strikes of seismic events dominated by roof breaking are mainly distributed in the range of 3°−80° and 150°−270°, and the dips are mainly distributed in the range of 70°−90°, with prominent agglomeration characteristics. Based on the common source rupture mechanism and location errors in the coal mine, the possibility of seismic event aggregation is analyzed, and the criteria of seismic aggregation are established. The risk prediction method and index based on the source rupture mechanism and location error calibration are constructed. The results of prediction examples show that the identification of seismic anomaly aggregation areas can be significantly enhanced by considering the source rupture mechanism and location error. When the seismic data is relatively complete, the IP threshold of the risk prediction index based on the source rupture mechanism and location error calibration is set to 0.7, and the accurate prediction of high magnitude events of different rupture types can be achieved.

Although the safety in the production of the mines in China has improved, coal bursts pose a serious threat to coal mines, especially deep mining. There have been eight coal bursts accidents with forty-eight deaths in the past five years. These accidents stem from the stopgap measures in terms of prevention and control and the unawareness of the occurrence mechanism of coal bursts. Furthermore, the sufficiently-mined mines in the east of China, such as the Juye and Yanzhou coal mines in Shandong province, are characterized by deep mining and strong disturbance. Whereas the insufficiently-mined mines in the west, such as the Ordos coal mine in Inner Mongolia province and Binchang coal mine in Shaanxi province, are characterized by high-intensity mining and hard rock strata. These complex mining environments create new challenges for preventing and controlling coal bursts. Therefore, the mechanism, prevention, and control of coal bursts have become a major engineering and scientific problem to be addressed urgently. The source-preventing method is the key issue in handling it. This paper reviewed the documents regarding the basic theory and numerical technology of coal bursts, monitoring and identification technology of dangerous zones, regional and local prevention and control technology, and equipment. Then, a new perspective of source prevention and control was proposed. Given this perspective, two scientific questions were detailed, including the source properties and prevention and control principles of coal burst during the process. Furthermore, four technical questions were also discussed, containing the fine simulation technology for the whole process of coal burst, the monitoring technology of coal rock stress and full-scale overburden structure in the entire life cycle of the mine, the accurate and intelligent identification technology of the danger zone with the proneness of coal burst, the collaborative prevention, and control technology of coal burst in the coal mine. Finally, the corresponding prevention and control methods and technical frameworks were formulated according to the characteristics of production and new mines. The findings will create a new way to prevent and control coal bursts. It also provides theoretical bases and technical support for the “zero bursts” goal for coal mines.

The loading mine stiffness and the post-peak stiffness of a coal pillar are important factors affecting the occurrence of coal bursts. In order to systematically study the mechanism of coal bursts and pillar bursts based on local mine stiffness theory, a laboratory-scale coal burst experiment system has been developed. The system is mainly composed of static loading system, energy storage system, variable stiffness loading system, excavation system and multi-source information monitoring system. The main innovations of the test system are as follows: ① An excavation device is added to the loading system, which can induce the stress concentration of the specimen and the reduction of local mine stiffness through excavation in the pressure-holding state. Coal bursts will occur when the specimen is stressed to its bearing capacity and the local system stiffness is lower than the post-peak stiffness of the specimen. ② The loading system is equipped with an energy storage device of oil cylinder airbag accumulator, which can store energy during loading. ③ A variable stiffness loading device is set up to adjust different loading stiffnesses by adjusting the initial airbag pressure of airbag accumulator. ④ The experiment system can reproduce the whole process of specimen from loading-stabilization-excavation-burst in laboratory, which makes it possible to monitor the strain of coal pillar during the whole process of coal bursts and observe the burst process. The accuracy and reliability of the simulation equipment are verified by preliminary laboratory tests on high-strength concrete blocks and realistic coal samples. The test results show that under the condition of low stiffness loading, the unstable failure of coal pillars can be effectively induced by excavating bottom samples, and the failure position extends from the low stiffness side to the high stiffness side. The damaged central residual coal pillar is dumbbell shaped under the action of top and bottom plate friction, and is cut off at the center by a transverse sawtooth crack penetrating the sample, resulting in a significant reduction in the bearing capacity of the coal pillar. The development of the experiment system can reproduce the whole process of coal bursts from loading, pressure stabilization, excavation and unstable failure in the laboratory from the perspective of local mine stiffness, and can provide an experimental basis for the mechanism of coal bursts in coal mines.

AbstractCoal bursts caused by mining-induced seismicity occur in the working face in steeply inclined and extra thick coal seams (SIETCSs). This article presents a case study in SIETCS through discrete element simulation as well as field investigation. The evolution of the coal burst was studied from the perspective of stress distribution, crack propagation and coal fragment ejection. The results showed that dynamic failure mainly occurred in the coal near the roof. The deep bottom coal and the top coal near the roof are under high static stress due to the clamping effect of the roof and floor and the rotation of the deep roof. The coal burst in the working face was triggered by mining-induced seismicity. The coal burst occurred when the sum of the static stress and the dynamic stress caused by the mining-induced seismicity exceeds the sum of the ultimate strength of the coal and the support strength, which was called the ‘clamping-rotation-dynamic loads’ mechanism. During the coal burst, the cracks developed rapidly into the deep bottom coal and the top coal on the roof side. The results can serve as an important reference for the coal burst failure mechanism in the working face in SIETCSs.

Water injection, as a widely used technique to prevent coal burst, can restrain the fractured coal seam and released the energy storage. In this study, laboratory tests were firstly carried out on standard coal specimens with five different water contents (i.e., 0%, 0.6%, 1.08%, 1.5%, 2.0%, and 2.3%). The failure mode, fragment size, and energy distribution characteristics of coal specimens were investigated. Experimental results show that strength, elastic strain energy, dissipated energy, brittleness index, as well as impact energy index decrease with increasing water content. Besides, the failure mode transitions gradually from splitting ejection to tensile-shear mixed failure mode as water content increases, and average fragment size shows positively related to water content. Moreover, scanning electron microscope tests results indicate that water in coal sample mainly causes the mineral softening and defects increase. Furthermore, a numerical model containing roadway excavation was established considering the water on coal burst prevention. Modelling results revealed that water injection can reduce degree of coal burst and ejection velocity of coal blocks, while it will raise up the depth of crack zone and surface displacement of roadway. Combined with laboratory tests and numerical results, the micro mechanism, energy mechanism, and engineering significance of water injection on coal burst prevention were finally analyzed. [ABSTRACT FROM AUTHOR]

The rock burst induced by the mutual disturbance of mining and excavation is significantly influenced by high static load stress and external dynamic load disturbance. In this paper, the evolution characteristics and progressive damage mechanism of surrounding rock in the process of mutual disturbance of mining and excavation are systematically studied. The results show that the evolution of surrounding rock stress can be roughly divided into three stages: rapid rise in the early stage, continuous rise and step-like decline in the middle stage, and slow rise in the late stage. In the process of parallel mining, the overlying rock movement above the goaf shows the sequence of horizontal penetration of tiny fissures—fracture intensification transition to stratification—non-coordinated caving of middle–low overlying rock—obvious horizontal cracks in the upper key layer. Only under the quasi-static loading mining action does the upper key layer not reach the breaking condition. The wave side of the heading face which is close to the focal point is affected by the dynamic load disturbance, the acceleration duration is short, and the attenuation is relatively fast, so it is the area prone to the earliest impact failure in the face of mining disturbance. The conclusion is helpful to deepen the understanding of the coal burst mechanism of mutual disturbance of mining and excavation. [ABSTRACT FROM AUTHOR]

Abstract Under the effects of complex geological and stress environments, burst hazards continue to be a major challenge for underground space utilization and deep resources exploration as its occurrence can lead to personnel causalities, equipment damage and structural collapse. Considering the stress path experienced by in-situ coal body, cyclic loading appears in quite various forms for instance shearer cutting, overlying strata breakage, hydro-fracturing and blasting, during tunnel, mining and underground space utilizing process. The stability of the underground coal body subject to periodic loading/unloading stress is extremely important for maintain the function of designed engineering structure for waste storage, safe mining, roadway development, gas recovery, carbon sequestration and so on. The mechanical properties of hard rock subject to cyclic fatigue loads has been intensively investigated by many researchers as the rock burst induced by supercritical loads has long been a safety risk and engineering problems for civil and tunneling engineering under deep overburden. More recently, the mechanical properties of coal samples under cyclic fatigue loads is investigated from the aspect of hysteresis, energy dissipation and irreversible damage as the burst hazards of brittle coal is rising in many countries. However, the crack propagation and fracture pattern of brittle coal need more research to understand the micro mechanism of burst incubation subject to cyclic fatigue loads as brittle coal can store more elastic strain energy and rapidly release the energy when its ultimate strength once reached. This research studied the internal crack status corresponding to different cyclic fatigue loading stage of brittle coal samples. The AE monitoring was applied during the uniaxial and cyclic loading process of brittle coal samples to record the crack intensity of samples at different loading stages. The damage evolution curve corresponding to loading status was then determined. The fracture pattern of coal samples determined by micro-CT scan was observed and discussed. It has been found by this paper that brittle coal of uniaxial compression tests demonstrated sudden failure caused by major splitting fracture while that of cyclic fatigue tests experienced progressive failure with mixture fracture network.

Directional hydraulic fracturing (DHF) is more and more widely used in coal mines in China for hard roof and coal burst control. The key to this technology is to determine the crack initiation pressure that affected by the shape of the artificial notch and the stress state around the fracturing hole. Reasonable and simple formula for fracturing pressure calculation is essential since the fracturing pump used in coal mines is usually limited by the harsh conditions and hardly replaced once selected. Based on the superposition principle, the simplified 2D model of DHF was established as the elliptical hole with the internal pressure and solved by using the complex functions method. The analytical solution of tangential stress on the inner surface was obtained meanwhile the corresponding criterion of fracturing pressure can be set up. Considering the characteristics of DHF in coal mines, we further got a simplified formula that controlled by the ratio of major to minor axis of the ellipse-like notch, the ratio of the minimum to the maximum principal stress, as well as the tensile strength of the rock. The formula also gave a guide to the design of the notch that major diameter should be at least twice the minor diameter, and the optimal solution for the ratio is to 2～4 and recommended 4, which can resist the initiation pressure to a large extent affected by the in-situ stress. Once the pressure of the fracturing fluid is high enough to satisfy the equation cracks would arise at the tips of the notch along the major axis which belongs to mode Ⅰ crack and would grow unsteadily and rapidly. A PFC simulation model was used to verify the analysis, the results of which are very consistent with the theoretical solutions.

The strain energy storage index WET was widely used to evaluate coal burst liability, but the scientific evidence for selecting the unloading stress level interval (around 80% of peak strength) remains lacking, and WET can not reflect the energy storage and dissipation ratio (ESD ratio) of the whole pre-peak stage for coal materials. In this study, these two key problems in WET calculation and application were solved based on the linear energy storage (LES) law. The LES law was defined as the linear relationship between the elastic strain energy and input strain energy for solid material during loading. Using the LES law, the elastic strain energy and dissipated strain energy of at 10 types of coals were calculated precisely, and ideal ESD ratio and general ESD ratio at any stress level will be obtained subsequently. The results also show that WET is extremely close to the ideal and general ESD ratio, which proves that the selecting stress level of WET calculation is scientific and reasonable. Furthermore, the general ESD ratio converges to the peak ESD ratio (namely peak strain energy storage index WET P ) as stress level increases. Compared with WET, Wp ET not only reflects the ESD ratio of coal materials over the whole pre-peak loading stage, but also exhibits excellent stability. Consequently, Wp ET is suggested as a new evaluation index of coal burst liability. [ABSTRACT FROM AUTHOR]

Practice and theory research proved the "square effect" during longwall mining with hard–thick strata lying on the coal seam, which could cause severe underground pressure and even dynamic disasters, such as coal burst; therefore, it became a key area and stage that need special attention. The combined active–passive seismic computed tomography (CT) was introduced to detect the abutment stress concentration in the coal seam. The results of active–passive CT inversion show that the "square effect" appears as early as the workface ahead of the theoretical position of 50 m with a 100 m significant influencing zone, which provides a strong guarantee for accurate risk evaluation of coal burst. Precursor information before the "square effect" can be identified based on the everyday total energy of mining tremors, which had period peaks in this case. The everyday average energy of mining tremors indicates that the seismic type during the "square effect" stage belonged to a foreshock–mainshock pattern. The combination of the seismic events and CT can improve the accuracy of coal burst danger distinguishing notably. The research can provide worthwhile guidance for the monitoring and prevention of coal burst hazards in similar conditions. [ABSTRACT FROM AUTHOR]

Mining-induced seismicity-triggered coal bursts (MISTCB) have become a major impediment to the safety of underground coal mining. Based on a severe MISTCB that occurred in China, this paper investigates the mechanism and control strategy of the MISTCB. A large-scale numerical model was built using the Universal Distinct Element Code (UDEC). Crack development and stress evolution of the MISTCB is analysed. In addition, the effect of mining-induced seismicity amplitude on the MISTCB is discussed. It is shown that severe dynamic failure occurred at both sidewalls and the floor of the roadway, including tensile failure near the roadway surface and shear failure in regions further away from the surface. After the coal burst, the distances between the two sidewalls and between roof and floor are 2.7 m and 3.1 m (4 and 5 m before the MISTCB). The maximum ejection velocity is up to 27.2 m/s. Mining-induced seismicity plays a key role for a MISTCB, whereas the amplitude (energy) is decisive for the strength of the dynamic failure. Increasing amplitude means increasing dynamic stresses, increasing ejection velocities of fragments and increasing deformations. However, the changes in dynamic stresses and deformations incl. damage patterns in the plastic, elasto-plastic and elastic zones are different. A zonation failure mechanism is proposed for the MISTCB. The obtained numerical results are in good agreement with the field measurements. The results are helpful for deeper understanding of the mechanism and to control the MISTCB. [ABSTRACT FROM AUTHOR]

As coal burst normally occurs in the area of high stress concentration, it is of significance to study the features of regional stress field in coal mines. Primitive stress field, mining-induced stress field and their coupling effect are investigated through the methods of theoretical analysis, field measurement, numerical simulation and wave velocity CT inversion, and the relationship among regional stress field, high-energy seismic events and coal bursts are analyzed. Investigation of the 3# mining district in Xingcun coal mine shows that: (1) Though stress concentration changes in the mining process, several special areas witnesses stress concentration in the whole mining process, such as the rise pillar area, several syncline axis areas and large fault areas; (2) Coal burst occurrence and high-energy seismic events have a close relationship with regional stress field. Coal bursts and high-energy seismic events tend to occur in areas of stable stress concentration, such as the rise area, several syncline axis areas and large fault areas. Targeted control of stress field for coal burst prevention is developed based on stress field detection. The process of targeted control of stress field for coal burst prevention is: detection of regional stress field based mainly on wave velocity CT, identification of stress concentration, implementation of destress measures to control the identified stress concentration. This method of stress field control was applied to LW3306 working face in Xingcun coal mine and coal burst hazards were effectively controlled in LW3306. [ABSTRACT FROM AUTHOR]

Coal burst is caused by a dynamic and unstable release of energy within the overstressed rock mass/coal during the mining process. Although the occurrence of coal burst is a result of the complex impacts of many factors, a major component of coal burst mechanism is associated with energy storage and release. This study reviewed the sources of energy that can contribute to a coal burst, principally strain and potential energy stored in the coal mass around excavations, and radiated seismic energy released by geological discontinuities. The energy balance concept proposed by [1] was utilised in numerical modellings to compute the radiated seismic energy in a modelling system and the kinetic energy of ejected rock/coal for a given burst scenario. The modelling results showed that the strain energy density (SED) around excavations increases with increasing mining depth and the maximum SED area migrates deeper into the coal. For the effect of geological features on both roadway and longwall face, the coal burst risk proneness can be assessed considering the proposed energy terms. According to the results of energy changes in excavations, the modelling predicts that for depths of ejection 2 m and 3 m the kinetic energy of a burst increases as the mining depth increases from 100 m to 1000 m, but for depth of ejection 1 m only increases until mining depth reaches 700 m and then decreases. The proposed energy-based model indicators can deepen the understanding of energy changes and the associated coal burst risks for different mining conditions. [ABSTRACT FROM AUTHOR]

Under the effects of complex geological and stress environments, burst hazards continue to be a major challenge for underground space utilization and deep resources exploration as its occurrence can lead to personnel causalities, equipment damage and structural collapse. Considering the stress path experienced by in-situ coal body, cyclic loading appears in quite various forms for instance shearer cutting, overlying strata breakage, hydro-fracturing and blasting, during tunnel, mining and underground space utilizing process. The stability of the underground coal body subject to periodic loading/unloading stress is extremely important for maintain the function of designed engineering structure for waste storage, safe mining, roadway development, gas recovery, carbon sequestration and so on. The mechanical properties of hard rock subject to cyclic fatigue loads has been intensively investigated by many researchers as the rock burst induced by supercritical loads has long been a safety risk and engineering problems for civil and tunneling engineering under deep overburden. More recently, the mechanical properties of coal samples under cyclic fatigue loads is investigated from the aspect of hysteresis, energy dissipation and irreversible damage as the burst hazards of brittle coal is rising in many countries. However, the crack propagation and fracture pattern of brittle coal need more research to understand the micro mechanism of burst incubation subject to cyclic fatigue loads as brittle coal can store more elastic strain energy and rapidly release the energy when its ultimate strength once reached. This research studied the internal crack status corresponding to different cyclic fatigue loading stage of brittle coal samples. The AE monitoring was applied during the uniaxial and cyclic loading process of brittle coal samples to record the crack intensity of samples at different loading stages. The damage evolution curve corresponding to loading status was then determined. The fracture pattern of coal samples determined by micro-CT scan was observed and discussed. It has been found by this paper that brittle coal of uniaxial compression tests demonstrated sudden failure caused by major splitting fracture while that of cyclic fatigue tests experienced progressive failure with mixture fracture network. [ABSTRACT FROM AUTHOR]

In practical engineering, coal burst is usually caused by the combination of high geo-stress and dynamic loading. To study the dynamic response of coal in geo-stress conditions, numerical models of a coupled static–dynamic split Hopkinson pressure bar (SHPB) test system were established, based on which impact tests for coal specimens at different impact speeds and static pre-stress levels were conducted. The mechanical properties, energy characteristics and failure patterns of coal specimens under coupled static and dynamic loads were analyzed. The results show that when the pre-stress is constant, peak stress, the maximum strain energy and the maximum kinetic energy increase significantly with impact speed. Nevertheless, they are less affected by the static pre-stress, increasing linearly with a pre-stress level under lower impact speeds but becoming stable under higher impact speeds. In addition, weak dynamic loads may trigger the instability of the coal specimen in a high pre-stress condition. Overall, both the impact speed and static pre-stress have influence on the mechanical behavior and energy characteristics of coal specimens under coupled static and dynamic loads, but the influence of the impact speed outweighs that of the static pre-stress. [ABSTRACT FROM AUTHOR]

The energy supply effect caused by the stiffness difference between roofs and sidewalls is an important factor that induces strain coal bursts. In order to quantitatively reveal the energy supply mechanism of strain coal bursts, this paper first establishes a coal burst energy model of the rock–coal system and proposes the calculation formula of coal burst kinetic energy considering supply energy and the stiffness ratio of rock to coal. Then the whole energy evolution law of the rock–coal system with different stiffness ratios is researched by using the numerical simulation method, and the whole process is divided into three stages. With the decrease in the stiffness ratio, the elastic strain energy of the coal changes little, while its kinetic energy is negatively correlated with the stiffness ratio in a power function. Meanwhile, the elastic strain energy and kinetic energy of the rock have power function relations with the stiffness ratio, too. When the rock–coal system is fractured, the kinetic energy of the coal comes from the release of elastic strain energy from the coal and the energy supplied from the rock. The energy supply rate is between 22% and 35% when the stiffness ratio changes from 3.0 to 0.5, and they show a linear relationship, while the supplied energy has a negative power function relationship with the stiffness ratio. [ABSTRACT FROM AUTHOR]

As an inherent property of the accumulation of elastic energy and the sudden instability failure of coal, coal bursting liability (CBL) is the basis of the research on the early warning and prevention of coal burst. To accurately classify the CBL level, the support-vector-machine (SVM) method was introduced in this paper, and the dynamic failure time (DT), elastic energy index (WET), impact energy index (KE) and uniaxial compressive strength (RC) were selected as the classification indexes. An imbalanced sample set, containing 95 groups of measured data of CBL, was established, and eight SVM classification models were constructed, based on different kernel functions and swarm-intelligence-optimization algorithms. Focusing on the problem of sample imbalance, the classification accuracy, A, F1-score and kappa coefficient were used to comprehensively evaluate the classification performance of SVM models, and the grey-wolf-optimizer SVM (GWO-SVM) model was selected as the best model in this paper, reaching the highest accuracy of 98.9%. The GWO-SVM was applied to identify the CBL level of the 4# coal seam in Xiaozhuang Coal Mine and the 1# coal seam in the Wanfeng Coal Mine. The results of the engineering application are consistent with those from the engineering field, and show that the proposed model is scientific and practical, and can be a new method for CBL classification. [ABSTRACT FROM AUTHOR]

With the coal mines in western China entering the field of deep mining, the problem of coal burst is becoming more and more serious. According to the characteristics of deep mining, it is an urgent problem that requires the development of an efficient and reasonable coal burst prevention and control plan to guide project practices. This study takes the typical deep mining area in Ordos as the research background, according to the stress state of the coal mining area and the load form of induced coal burst, which, in Ordos deep mining, is divided into the typical and atypical type. The former is caused by the superposition of high in situ stress and strong mining-induced stress, while the latter is due to the combination of high in situ stress, strong mining-induced stress, and external stress disturbances. Combined with theoretical analysis, numerical simulation, and field measurement, it is shown that the stress level of the Ordos deep mining area is higher than that of the shallow original rock, and the difference of the three-dimensional stress between coal and rock mass is greater. The concentration degree and influence range of mining-induced stress obviously increase. Coal and rock mass are more prone to instability and failure due to external disturbances. Based on the stress control theory, the prevention and control strategies of coal burst in different types of deep mining are put forward. In addition, the prevention and control technology system of coal burst in the Ordos deep mining area is established. The field engineering practice has been carried out to realize the efficient prevention and control of coal burst. [ABSTRACT FROM AUTHOR]

To investigate the failure mechanisms of coal bursts in the longwalls of underground coal mines, a case study based on the real coal burst in the Tangshan coal mine occurring on 2 August 2019 was carried out to analyze the cause and basic theories of the coal burst and, thus, propose approaches and methods to mitigate the damage. The coal burst occurred mainly due to the sliding of coal from the longwall ribs and the simultaneous uplifting of the floor. As a result of the longwall retraction, the roof above the coal seam was too stable to collapse, forming a long hanging roof behind the longwall. Because the longwall acted as a fulcrum, the hanging roof acted like a saw, exerting massive loads on the longwall. As a result, the roof in front of the longwall tended to slope upward, leaving the underlying coal seam unconfined. Due to the horizontal stresses, the longwall ribs collapsed into the longwall, causing the coal seam to break out. These findings could help improve the fundamental understanding of the failure mechanisms of coal breakouts and, thus, aid in the development of measures to prevent such occurrences.

The development of stiffness theory is constrained by its contradiction with engineering experience. Several easily overlooked details of stiffness theory were clarified, and a qualitative evaluation formula for the risk of coal burst was provided. Then a novel structure factor called uneven stiffness coal seam structure (USCS), which consists of high stiffness zone (HSZ), low stiffness zone (LSZ), and contiguous roof and floor, was proposed. Many areas prone to coal bursts, such as thinning zones, bifurcating areas, magmatic intrusion areas, and remnant pillar affected areas of coal seam, are the HSZs of USCSs. Comparative analysis of the uneven stiffness coal seam under different roof conditions and examination of the simplified trisection model of the USCS were conducted. Then 6 groups of 14 simplified 2D models using COMSOL5.2 was constructed based on controlled variable method to simulate different responses of the USCS with varying parameters under same working conditions. The results demonstrate the following: (1) coal bursts occur only when both the failure criterion and the stiffness criterion are simultaneously satisfied, the risk of coal burst (rCB) is the product of the risk of failure (rF) and the risk of instability (rI). (2) The pressure concentration function of USCS facilitates stress concentration from LSZ to HSZ, thus raising the rF in HSZ. The stiffness reduction function of USCS reduces the local mine stiffness (LMS) of the HSZ, allowing the system to meet the stiffness criterion even with a hard roof, thereby raising the rI in HSZ and reconciling the contrast between stiffness theory and engineering experience. Failures within HSZ of the USCS enables the roof strata to release bending deformation energy without roof breakage. (3) The normal stress of HSZ is positively correlates with the value of ERHRKHSL/KLSH; The LMS of the HSZ is positively correlated with the value of ERKL/KHHRSLSH. The USCS boasts significant advantages in integrating and harmonizing various existing theories and explaining multiple specific types of coal bursts. By applying relevant USCS findings, new explanations can be provided for engineering phenomena such as the time-delayed coal bursts, the inefficient pressure relief in ultra thick coal seams, and the “microseism deficiency” observed prior to certain coal bursts.

Abstract Coal burst has become one of the most serious hazards in longwall coal mines of many countries, and extensive studies have been conducted on the mechanism, prediction, and prevention of coal bursts. However, most of these studies focus on qualitative descriptions of burst environments and specific case analyses. Few studies have been carried out to explore knowledge through a number of past coal bursts in longwall mines. The main objective is to quantitatively analyze the current burst‐prone conditions in longwall coal mines of China and to summarize corresponding lessons. A database consisting of 54 major coal bursts was established. The characteristics and contributing factors of involved coal bursts were analyzed quantitatively, and high‐risk areas that are common in coal mines were then identified. Finally, some suggestions and lessons were proposed. This study may help for identifying controlling factors and high‐risk areas at a specific mine, and it might provide insights into the control of coal bursts in longwall coal mines.

It is hard to control roadways effectively with a heightened burst risk using conventional support techniques, which may cause burst fatalities in the coal mine. Thus, an in-situ modification method, which involves artificially constructing a cracked zone and a reinforced zone, was proposed to improve the stability of the roadways with heightened burst risk. This paper investigated the efficiency to non of the in-situ modification method in improving burstroadway safety by performing a physical experiment. The results of the experiment indicated that the dynamic stress was obviously reduced in the modified roadway. Accordingly, the influence factors of the in-situ modification method were explored using numerical simulation. It was found that the thickness and the degree of damage to the cracked zone were key governing factors in reducing energy and improving roadway stability. The energy dissipation value increased as the thickness and the degree of damage to the cracked zone increased but showed a slower growth trend when the thickness and the degree of damage to the cracked zone increased to a certain value. In addition, the high sensitivity to dynamic load was found in parts of the roadway side exhibiting a larger stress reduction rate even with thinner cracked zone thickness and a lower degree of damage. This research provides an effective and economical method for coal roadways with heightened burst risk.

With the increase in mining depth, coal bursts have become a major challenge in the safe mining of steeply inclined and extra thick coal seams (SIETCSs). Based on a typical mining induced seismicity triggered coal burst (MSTCB) in SIETCS, a large-scale numerical model was developed using the Universal Distinct Element Code. The numerical model was calibrated and validated by laboratory results and field observations. The stress evolution, crack development and ejection velocity patterns in the MSTCB were analysed, and the effect of mining induced seismicity vibration velocity on the MSTCB was discussed. The results show that a triangular static stress concentration zone is formed in the coal on the roof side. And the high-energy mining induced seismicity leads to high dynamic stresses in the coal at the roof side rib and top of the headentry. Coal bursts occur under the superposition of static and dynamic stresses. The MSTCB results in tensile failure near the headentry surface and shear failure in the depth. The vibration velocity has a significant effect on the roof side rib and top of the headentry, while it has only a slight effect on the working face rib and bottom of the headentry. The dynamic stress and ejection velocity in the roof side rib and top of the headentry are positively correlated with the vibration velocity. Finally, measures for MSTCB prevention were proposed. The findings presented in this study can provide guidance for the prevention and control of MSTCBs in SIETCSs.

The true triaxial test can accurately simulate the dynamic and static load superposition environment of deep mining and then reproduce the spatial and temporal evolution process of coal-rock dynamic disasters. This study used a self-developed true triaxial coal-rock dynamic behavior test system to investigate the dynamic failure characteristics and mechanism of coal bursts under different mining-induced stress disturbances. The results show that the perturbation duration of the coal samples under quasi-static load decreases with the increase of the disturbance rate, and the perturbation stress level increases first and then decreases. The coal samples can accumulate higher strain energy and show progressive and dynamic failure. The perturbation duration and stress peak of the coal sample under the cycle load decreased with the increase of the cycle amplitude and frequency, and the coal sample first spalled off on the free surface. The damage then developed internally until the coal burst. The perturbation duration and stress peak of coal samples decrease with the increase of transient stress and the perturbation stress levels. The dynamic failure process of coal samples is straightforward, and the strength of coal burst is violent and is more difficult to predict. The conclusions obtained help to deepen the understanding of the triggering mechanism of coal bursts. [ABSTRACT FROM AUTHOR]

Seismic energy analysis is the basis of coal burst risk assessment. The prerequisite for utilizing seismic energy to quantify coal burst hazards is the accurate understanding of seismic energy attenuation. Thereby the characteristics of seismic energy attenuation were first systematically investigated in this paper. Based on the seismic data and 24 coal burst records during the period of sixteen months, a risk assessment method including three indexes (Static Intensity Index (SII), Dynamic Intensity Index (DII), and Risk Assessment Index (RAI)) was derived from seismic energy attenuation. In consideration of the static and dynamic response, the superposition effects of seismic energy were proposed to improve the performance of risk assessment. Results show that residual seismic energy (RSE) is relatively correlated with seismic energy, source radius, and energy attenuation coefficient; the higher seismic energy, source radius, and lower energy attenuation coefficient would result in higher coal burst risk. The case study demonstrated that SII could effectively predict the damaged area, but its prediction efficiency of high-magnitude events (HMEs) is relatively low; DII could predict damaged areas and HMEs, but may lead to risk overestimation; and RAI could efficiently predict the damaged area and HMEs. The sensitivity of the monitoring system and seismicity activeness could be the two main restrictions of the proposed method, leading to low efficiency or even false risk assessment. This paper sheds light on seismic energy utilization to risk prediction in underground coal mines. HighlightsThe attenuation response characteristics of seismic energy to different factors including seismic energy, source radius, and attenuation coefficient were investigated.A new assessment method based on seismic energy attenuation calculation was proposed to assess coal burst risks. Three seismic-based indexes considering static and dynamic response and their superposition effects were proposed to assess coal burst risk.Sensitivity of monitoring system and seismicity activeness could be the two main restrictions leading to low accuracy or even false in risk assessing, which implies that the proposed method could also have false judgements in the place where rare seismicity is monitored.

Abstract Ground support is widely implemented to mitigate dynamic rock failures in underground mines. This paper investigated the ground support requirements in burst-prone mines to mitigate the catastrophic dynamic rock failures of rock and/or coal bursts. First, the ground support principles and considerations in burst-prone conditions are identified. The objective of a ground support system is to increase the capacity to accommodate rock fracturing in a rockburst and, in turn, to minimize the kinetic energy of the ejected material. The support capacities of various yielding rockbolts and integrated support systems are then investigated using the test results in the laboratory. Apart from the energy absorption and yielding deformation capacity, the initial stiffness and energy absorption rate are also critical factors when applying yielding rockbolts in practice. Adding rope lacing and mesh strap to surface support elements can substantially enhance the support performance of the system. In practice, semi-analytical and empirical approaches are often used to determine the ground support elements in burst-prone areas. Semi-analytical methods first evaluate the support demand in burst risk zones and then select support elements according to their laboratory test results. Alternatively, empirical methods determine the ground support elements according to the locally established empirical rating scheme, which usually ranks the support capacities of various support systems based on ground support conditions and damage conditions. The outcomes of this study can provide insights into ground support strategies and assist the mining industry to develop effective coal burst control technologies.

To evaluate the coal burst proneness more precisely, a new energy criterion namely the residual elastic energy index was proposed. This study begins by performing the single-cyclic loading-unloading uniaxial compression tests with five pre-peak unloading stress levels to explore the energy storage characteristics of coal. Five types of coals from different mines were tested, and the instantaneous destruction process of the coal specimens under compression loading was recorded using a high speed camera. The results showed a linear relationship between the elastic strain energy density and input energy density, which confirms the linear energy storage law of coal. Based on this linear energy storage law, the peak elastic strain energy density of each coal specimen was obtained precisely. Subsequently, a new energy criterion of coal burst proneness was established, which was called the residual elastic energy index (defined as the difference between the peak elastic strain energy density and post peak failure energy density). Considering the destruction process and actual failure characteristics of coal specimens, the accuracy of evaluating coal burst proneness based on the residual elastic energy index was examined. The results indicated that the residual elastic energy index enables reliable and precise evaluations of the coal burst proneness.

The rock burst induced by the mutual disturbance of mining and excavation is significantly influenced by high static load stress and external dynamic load disturbance. In this paper, the evolution characteristics and progressive damage mechanism of surrounding rock in the process of mutual disturbance of mining and excavation are systematically studied. The results show that the evolution of surrounding rock stress can be roughly divided into three stages: rapid rise in the early stage, continuous rise and step-like decline in the middle stage, and slow rise in the late stage. In the process of parallel mining, the overlying rock movement above the goaf shows the sequence of horizontal penetration of tiny fissures—fracture intensification transition to stratification—non-coordinated caving of middle–low overlying rock—obvious horizontal cracks in the upper key layer. Only under the quasi-static loading mining action does the upper key layer not reach the breaking condition. The wave side of the heading face which is close to the focal point is affected by the dynamic load disturbance, the acceleration duration is short, and the attenuation is relatively fast, so it is the area prone to the earliest impact failure in the face of mining disturbance. The conclusion is helpful to deepen the understanding of the coal burst mechanism of mutual disturbance of mining and excavation.

Practice and theory research proved the “square effect” during longwall mining with hard–thick strata lying on the coal seam, which could cause severe underground pressure and even dynamic disasters, such as coal burst; therefore, it became a key area and stage that need special attention. The combined active–passive seismic computed tomography (CT) was introduced to detect the abutment stress concentration in the coal seam. The results of active–passive CT inversion show that the “square effect” appears as early as the workface ahead of the theoretical position of 50 m with a 100 m significant influencing zone, which provides a strong guarantee for accurate risk evaluation of coal burst. Precursor information before the “square effect” can be identified based on the everyday total energy of mining tremors, which had period peaks in this case. The everyday average energy of mining tremors indicates that the seismic type during the “square effect” stage belonged to a foreshock–mainshock pattern. The combination of the seismic events and CT can improve the accuracy of coal burst danger distinguishing notably. The research can provide worthwhile guidance for the monitoring and prevention of coal burst hazards in similar conditions.

In the context of complex geological environments, coal burst liability (CBL) evaluation struggles with uncertainty and fuzziness of indices and with obtaining satisfactory accuracy. Therefore, an improved connection cloud model (ICCM) is proposed for CBL evaluation based on set pair analysis referring to four indices. The numerical characteristics of the ICCM, namely expectation (Ex), entropy (En), hyper-entropy (He) and parameter (f), were determined by set pair analysis and classification standards. Then, the index measurement-based entropy weight method and the analysis hierarchy process (AHP) were used to measure clearly the importance of each index. Finally, Euclidean distance was employed to classify the CBL objectively, making full use of the valuable information mined from the data. An updated CBL database (of 147 data records) was constructed to validate the potential of the proposed algorithm for CBL classification. Additionally, a graphical user interface was developed to make the CBL evaluation visible. The classification metrics of the ICCM, i.e., accuracy and Kappa coefficient, were 0.88 and 0.772, respectively, which were better than those of the other conventional uncertainty methods. The results reveal that the proposed ICCM is a prospective tool for uncertainty information treatment and subjectivity removal in the field of coal burst control. [ABSTRACT FROM AUTHOR]

Seismic hazards are typical mining hazards causing dynamic failure of coal and rock mass, which greatly threatens the safety of personnel and equipment. At present, various seismic analysis methods are used to assess seismic risks but their accuracy is significantly limited by the incompleteness of seismic data. The probability of detecting earthquakes (PDE) method has been proven as a powerful means for retrieving missed seismic events and enhancing the seismic data integrity in mines. However, to date, the reliability of the results of the PDE method has not been assessed and the highly integrated seismic data have not been linked with the actual hazard potential. To fill these gaps, this paper investigated the impacts of the seismic data volume used for calculation and the modification of the layout of sensors on the reliability and robustness of the PDE method. The event counts and seismic energy were compensated using the PDE method, correlated with strong seismic events. The results indicated that the compensated seismic data presented higher accuracy in locating future hazardous events than before. This research provides references on enhancing the performance of seismic analysing methods for seismic risk assessments. [ABSTRACT FROM AUTHOR]