Friction stabilizers for rock bursts hazard mitigation in deep mines’ environments

To address the issues of complex rock mass movement and dynamic disasters during the mining of near-vertical extra-thick coal seams, this study takes the + 425 level B3 + 6 working face of Wudong Coal Mine as the research background, aiming to investigate the mechanism of dynamic disasters. By adopting theoretical analysis, on-site investigation, and physical simulation, the study established a mechanical model for rock pillar deformation and failure, analyzed the failure modes of rock pillar as well as roof and floor, and their impacts on coal seam stability, revealed the corresponding disaster-inducing mechanism, and proposed a pressure relief and rock burst prevention technology. The results show that the deformation and prying rotation of rock pillar are the main factors causing strain energy accumulation in coal-rock masses, while the fracture of rock pillar and the toppling-sliding of roof and floor are the primary forms of dynamic impact loading. Specifically, the large-scale fracture depth of rock pillar reaches 350m, and the fracture step distance of the immediate roof exceeds 43m. To prevent and control rock burst, a pressure relief and rock burst prevention technology was proposed, which achieves pressure relief through deep-shallow hole blasting on the roof and floor. Combined with the numerical simulation analysis of deep-shallow hole blasting, the significant reduction in electromagnetic intensity, the gradual decrease in the frequency of microseismic events, and the gradual reduction in energy have verified the pressure relief effect of this technology. This study provides an effective technical approach for the safe mining of coal seams.

The thermal-hydro-mechanical (THM) coupling and a strong mining disturbance environment all have a significant impact on deep ground engineering excavations, which increases the risk of a rock burst disaster. The independently developed THM multi-physics coupling apparatus enables replication of intricate geological conditions in engineered rock formations, with high-strain-rate compression experiments on deep-buried rock specimens being implemented through a split Hopkinson pressure bar testing platform. The fracture surface microstructure and the pore structure of the rock after impact are characterized by SEM and NMR. Results show that the dynamic stress-strain curve exhibits nonlinear behavior, accompanied by a significant 'plastic platform area.' Under the same temperature and pre-static stress, the energy time-history evolution distribution of rock in the process of dynamic compression has the characteristics of synchronous and different amplitudes. The energy reflection coefficient and energy dissipation coefficient obey a good exponential function and a Gaussian function relationship with water pressure, respectively. 'Compression-shear crushing failure → inclined shear boundary failure → fracture failure' is the development trend of the overall failure mode of rock when temperature and water pressure increase. The dynamic damage threshold is between 0.35 and 0.36. Microscopically, it shows a transformation trend of intergranular fracture, complex fracture, and transgranular fracture. NMR analysis reveals that elevated water pressure enhances the structural integrity of rock pores, accompanied by a reduction in pore dimensions and a progressive decline in overall porosity. A mechanical model of sliding microcrack propagation under THM coupling and impact load is constructed. By analyzing the variation patterns of crack initiation points under different operating conditions, the accuracy and adaptability of this model were validated.

The change of stope migration caused by the failure and instability of the overlying thick key strata has a control effect on the occurrence of rock burst in front of the working face. The main disaster-causing factors of rock burst in front of the working face are explored to predict and prevent rock burst. Through the distribution characteristics of microseismic energy events, it is determined that the instability of hard roof has a great influence on the mining of working face. The influence mechanism of the instability and fracture of the overlying hard rock strata on the rock burst of the working face is clarified, and the distribution of the advance abutment pressure of the working face and the energy accumulation of the coal and rock mass under the static load condition are calculated by establishing the mechanical model of the advance abutment pressure of the working face under the condition of full mining. The superposition of dynamic and static load energy on the working face by the initial and periodic instability fracture and synergistic fracture energy release of the overlying hard rock strata is calculated theoretically. It is determined that the superposition energy transmitted to the working face by the synergistic fracture of the middle and low hard rock strata is 1.23 × 104 J, which is higher than the critical energy of Gengcun rock burst. The low hard rock layer is determined as the monitoring target layer, and the on-line monitoring scheme of hard rock layer activity is established. The dynamic change of anchor cable data of stress evolution law of low hard rock layer in the process of working face mining is quantitatively determined, which reflects the stress evolution law of coal and rock mass in front of working face, and quantitatively determines the three-stage division of the influence of working face mining on coal and rock mass in front of working face.

This study examines the effects of synergistic treatment with surfactants and compound acids on the mechanical properties (e.g., strength and deformation characteristics) and microscopic features (e.g., pore structure, surface wettability, and chemical composition) of coal. The results indicate that acid treatment weakens coal strength, and the addition of sodium dodecyl sulfate (SDS) further exacerbates this effect. Acidification significantly reduces acoustic emission energy, electromagnetic radiation energy, and infrared radiation temperature released by coal. Moreover, SDS modifies the chemical structure of coal, reducing aromatic content by ~ 30% and fat content by ~ 50% compared to untreated coal. Under the synergistic effect of SDS, acid-induced erosion reaches its maximum. The decrease in fractal dimensions DW and DS indicates that SDS promotes coal pore connectivity. Furthermore, molecular dynamics simulations reveal that the synergistic interaction between surfactants and compound acids enhances water molecule diffusivity, improving coal wettability and promoting pore and fracture network development. This synergistic effect not only further reduces coal strength but also significantly enhances permeability, which is vital for mitigating stress accumulation in coal seams. This provides critical theoretical and technical guidance for the effective prevention and control of dynamic disasters such as rock bursts.

Numerical investigation of rock burst induced by excavation unloading near structural planes in deep tunnels

Control of rock burst during deep tunnel blasting excavation based on energy release process optimizing

The persistent occurrence of rock burst phenomena during roadway excavation poses a critical safety challenge in modern underground mining operations. This research systematically investigates zonal evolution patterns of acoustic emission (AE) events, developing quantitative indicators to evaluate rock burst risks and progressive damage quantification in surrounding rocks and reveals the failure mechanisms with rock burst. The results show that the elastic strain energy in the surrounding rock instantly releases suddenly, causing the deformation and failure of the shallow damaged surrounding rock and inducing rock burst in the excavation roadway. In horizontal, the risk of rock burst increases with the increase of horizontal tectonic stress; in vertical, the risk first increases and then decreases with the increase of mining disturbance stress. Dynamic stress has a significant impact on the degree of damage to the surrounding rock and increases the possibility that rock burst. The coordinated prevention and control method of "pressure relief-load reduction - reinforcement" for roadway excavation was proposed based on the energy zoning characteristics of the roadway effectively reduces the risk of rock burst during the roadway excavation process and provides certain reference experience for the prevention and control of rock burst in roadway excavation.

Rock burst is one of the most typical dynamic disasters in the process of coal mining. Energy-absorbing components are key to anti-impact equipment. Exploring the mutual feedback relationship between energy-absorbing components and columns for the prevention and control of roadway rock burst is of great significance. In this study, an arc-shaped energy-absorbing component was designed, and its energy-absorbing characteristics were analyzed. The finite element analysis results of the arc-shaped energy-absorbing component were verified via the crushing test machine. The energy-absorption effect of pre-folded, diameter-expanded, eversion, and arc energy-absorbing columns under impact is compared horizontally. The results show that the supporting force is stable during the crushing deformation of the arc-shaped energy-absorbing component, and the average supporting force measured in the test is 1145.35 kN. Compared with the other three energy-absorbing columns, the arc-shaped energy-absorbing column has a lower emulsion pressure peak and the maximum pressure fluctuation amplitude during the impact process; it also has a better deceleration effect on the quality mass. During the impact process, the influence of the arc-shaped energy-absorbing component on the liquid impact in the column is summarized into three stages, namely approximate elasticity, flexible yield energy-absorbing, and approximate rigidity, which can achieve the peak clipping effect on the liquid impact and improve the impact resistance of the column.

The disturbance of vibration wave will have a great influence on the internal stress, pore fissure and gas adsorption of coal and rock mass. The typical earthquake and mine earthquake waveform records in the mining area are selected. Combined with the comprehensive histogram of the working face, the calculation model is established by UDEC software, and the propagation attenuation law of vibration wave in the presence or absence of chamber is analyzed. The calculation results show that: (1) Under the condition of no chamber, the peak velocity of seismic wave decreases exponentially with the increase of source distance, and the fitting accuracy R2 of seismic wave and mine seismic wave attenuation characteristics is 0.96 and 0.98 respectively. (2) The peak velocity of seismic wave decreases exponentially with the increase of focal distance under the condition of chamber. However, there is a transition point at the chamber (goaf), which attenuates at a faster speed before passing through the chamber, and the attenuation speed slows down after passing through the chamber. The attenuation rate of the peak velocity of the earthquake and the mine earthquake reached 53.9% and 46.8% respectively when passing through the chamber. (3) The peak velocity of the vibration wave is the largest at the left/right foot of the chamber, and the peak velocity of the vault is the smallest. (4) The velocity attenuation curve of the source ring of the seismic wave decreases faster in the vertical direction than in the horizontal direction, and the attenuation in the vertical direction is particularly obvious after passing through the chamber. The propagation and attenuation characteristics of vibration waves are of great significance to the prevention and control of rock burst in coal mines, the development characteristics of coal and rock pores and fractures, and the early warning of gas disasters.

Hard coal seams in the Ordos region are key geological factors contributing to rock bursts. To overcome the limitations of conventional drilling pressure-relief techniques—such as insufficient unloading efficiency, reliance on high-density multi-round drilling, and support failure—this study establishes a non-isobaric stress field model and analyzes the influence of coal seam strength and drilling diameter on the radius of the drilling-induced plastic zone. Based on this analysis, a coupled “shallow support and deep pressure relief” unloading-support technology was proposed. A 70-m on-site comparative industrial test was conducted using coal-powder monitoring, coal-cannon monitoring, stress monitoring, and surrounding-rock deformation monitoring to evaluate pressure-relief and support performance. The results show that the plastic zone radius is mainly controlled by coal strength and borehole diameter, with diminishing benefits when enlarging the diameter beyond a threshold. The enhanced pressure-relief zone produced 3.1 times more coal powder than traditional drilling, and coal-cannon events concentrated in the 7–14 m range effectively released accumulated elastic energy. Post-relief stress peaks were significantly reduced and recovered more slowly. In terms of roadway stability, anchor-cable stress remained lower and more stable than under conventional drilling, with roadway side convergence and roof–floor convergence reduced by 63% and 51%, respectively. A comprehensive mechanical drilling–based anti-burst technology and equipment system was developed and successfully applied in engineering practice. These findings provide theoretical support and practical guidance for pressure relief and support strategies in hard coal seams of the Ordos region and similar mining conditions.

In recent years, with the deepening of mining and tunnel excavation operations, the incidence of rock burst has also increased, prompting people to attracting increasing attention to microseismic monitoring technology. The location algorithm of microseismic events is the core of microseismic monitoring. In this study, a hybrid optimization algorithm, BP-GA-GN, which combines genetic algorithm (GA), BP neural network (BP) and Gauss-Newton method (GN), is introduced. The BP-GA-GN algorithm optimizes the initial weights and thresholds of the BP neural network through GA to avoid local optimum. The BP neural network is used to learn the nonlinear mapping between the sensor arrival time difference and the source position. Combined with the physical model constraints of GN, fine convergence is performed. We prove the robustness of the BP-GA-GN algorithm through a large number of numerical simulations. Compared with the traditional single algorithm, the algorithm shows excellent performance. Subsequently, the high precision and high efficiency of the method are further highlighted in the field data test of mine environment and tunnel environment. The average errors are 0.42 m and 2.54 m, respectively, rendering it a valuable tool for real-time microseismic monitoring. This study overcomes the limitations of traditional positioning methods. The algorithm can achieve high-speed training and high precision, thus significantly improving the early warning effect of rockburst risk.

A Highly Brittle Similar Material for Rock Burst Simulation Tests: Quantitative Evaluation and Experimental Validation

As shallow coal reserves are diminishing in China, mining operations are extended to deeper levels, such that characteristics like high geopressure, intense gas adsorption, and reduced permeability become obvious. The mining environment alters significantly. To monitor geological hazards including rock burst during coal mining, this paper presents a time series prediction model for micro-seismic signals by quadratic modal decomposition and a TCN-Transformer network. At first, the micro-seismic signal is primarily decomposed by CEEMDAN. The decomposed Intrinsic Mode Functions (IMFs) are classified and reconstructed by fuzzy entropy. Then, a secondary decomposition is performed by VMD to uncover the signal’s latent features. Thereafter, the time series prediction model is developed by integrating the TCN network’s multi-scale feature extraction capabilities with the self-attention mechanism of the Transformer network. The experimental results demonstrate that the model effectively captures both local and global features within micro-seismic signals for enhancing prediction accuracy. Validation with micro-seismic monitoring data from an actual coal mine in Xinjiang confirms the model’s strong fitting ability and robustness, and further indicates the early warning capabilities for rock robust. The proposed method can offer reliable technical support for safe coal mine operations.

Mine disasters occur frequently during deep coal-mining operations in China; however, current monitoring and early-warning methods for rock bursts remain insufficient. To address this, this paper proposes an early-warning method for rock bursts based on the fractal dimension of microseismic energy. Through the establishment of an integral expression relationship between microseismic energy and fractal dimension, the spatio-temporal distribution characteristics of microseismic events are analyzed, revealing the precursor patterns of rock bursts. The results indicate that prior to the occurrence of a rock burst, parameters such as microseismic energy, event frequency, and fractal dimension all exhibit significant precursor characteristics. Furthermore, the temporal evolution of the fractal dimension can be divided into four distinct stages: stable, early-warning, deformation, and re-stabilization periods. This method provides a new approach for the quantitative early warning of rock bursts.

Floor blasting has been demonstrated to reduce roadway floor heaving by interrupting the transmission of floor stress, thereby preventing floor rock burst. This study establishes a roadway floor blasting similarity model test system, which incorporates a swing impact testing facility, a high-speed digital image correlation apparatus, and an ultra-dynamic data acquisition instrument. The initial comparison was made between the effects of floor pressure relief measures on roadway dynamic load response characteristics under high-stress section dynamic load conditions. Furthermore, numerical analyses using the RHT constitutive model within LS-DYNA thoroughly investigated the influence of in-situ stress levels, the intensity of dynamic loads, and their placement. The experimental and numerical findings suggest that floor blasting significantly reduces the peak acceleration and stress amplitude of roadway rock mass under dynamic load conditions. Roadway that employ floor blasting for pressure relief have been shown to maintain an intact floor after strong dynamic loads. Additionally, the horizontal-to-vertical stress ratio exerts a predominant influence on crack propagation patterns, and a lateral pressure coefficient that exceeds 1.6 exacerbates asymmetric damage. The influence of dynamic load intensity and application location on damage asymmetry is significant, with the wavefront side exhibiting higher crack complexity.

Coal–rock composite structures are prevalent in deep coal mining operations, and their mechanical behavior plays a crucial role in maintaining tunnel stability and understanding the mechanisms of dynamic disasters, such as rock bursts. In this context, the present study investigates coal–sandstone composite specimens through systematic laboratory uniaxial compression tests. The experimental results reveal that failure predominantly occurs in the coal region, which is the key factor governing the overall mechanical performance of the composite. Specifically, under uniaxial compression, as the coal–sandstone height ratio increases from 1:1 to 2:1 and 3:1, the peak strength drops from that of pure sandstone (46.17 MPa) to 25.17/21.77/19.52 MPa, corresponding to reductions of 45.47%, 52.83%, and 57.75%, respectively. Meanwhile, the peak strain increases overall; for reference, pure sandstone exhibits a peak strain of 0.7965%, while the composites display a deformation response closer to that of coal. In addition, in terms of acoustic emission (AE), cumulative ringing counts at 2:1 and 3:1 are reduced by about 80.23% and 90.05% relative to 1:1. To further analyze AE data, the proposed “denoise-then-cluster” workflow markedly outperforms the direct clustering example; the silhouette coefficient improves from −0.32 to 0.53 for specimen 1:1-1 and from 0.63 to 0.88 for 2:1-1. Furthermore, under the 3:1 condition, shear cracks account for 75.33% of the total, indicating a coal-dominated brittle shear failure mechanism. Collectively, these findings contribute to a deeper understanding of the rock burst initiation mechanism in coal–sandstone composites and provide theoretical support for the stability evaluation and disaster prevention of coal–rock composite structures.

Coal seam drilling for pressure relief is one of the most widely adopted measures to mitigate rock bursts. However, conventional drilling methods exhibit limited effectiveness in hard coal seams and may compromise the integrity of roadway support structures. To optimize traditional pressure relief drilling parameters, this study investigated the influence of coal seam strength and borehole diameter on pressure relief efficiency based on elastoplastic mechanics theory. A novel mechanical reaming technology for pressure relief and rock burst prevention in hard coal seams was developed and subjected to field trials. Multiple monitoring techniques were employed to evaluate its performance in terms of both pressure relief and support stability. The conclusion was drawn that: (1) The higher the strength of the coal seam, the smaller the radius of the plastic zone of the borehole; therefore, the pressure relief effect of the borehole in the hard coal seam is poor. After increasing the diameter of the borehole, the radius of the plastic zone increases, but when the diameter of the borehole increases to 300 mm, the increasing trend of the radius of the plastic zone weakens. Thus, only increasing the diameter of the borehole cannot improve the pressure relief effect of the borehole without limit. (2) An innovative hard coal seam pressure relief and anti-impact technology, termed support, deep pressure relief, unloading-support coupling, the elastic energy accumulated in the coal body through a deep large borehole while utilizing a shallow small borehole to maintain the bearing capacity of the support structure, thereby achieving a balance between pressure relief and support. (3) In comparison to conventional drilling areas, the volume of coal seam drilling powder in the mechanical reaming area has increased by 3.1 times, and the number of per meter has risen by 70%, significantly enhancing the pressure relief effect. Additionally, the anchoring force of the roof anchor cable in the mechanical reaming area has decreased by up to 29%, the variation in tension of the anchor cable on the sides has been reduced by up to 51.8%, the convergence of the two sides of the roadway has diminished by up to 63%, the convergence between the roof and floor has decreased by up to 51%, and both the stress on the support structure and the deformation of the surrounding rock have been significantly reduced. These research findings provide a theoretical foundation and technical support for the prevention and control of rock bursts in similar hard coal seam mining roadways.

To alleviate strong strata-pressure bursts during ultra-thick coal extraction, we selected the 26 m number five seam of the Chenjiagou Coal Mine as a full-scale prototype. Three objectives were pursued: (1) elucidate the initiation mechanism of high-energy roof failures under top-coal caving (TCC); (2) quantitatively link the failure sequence of key strata to burst intensity; and (3) deliver field-oriented prevention criteria. A 1:300 physical similarity model and UDEC plane-strain simulations were combined to monitor roof deformation, stress evolution and dynamic response during extraction. Results demonstrate that pressure bursts are driven by abrupt kinematics of the overburden, triggered by sequential breakage of key horizons: the secondary key stratum collapsed at 130 m face advance, followed by the main-key stratum at 360 m. Their combined rupture generated a violent energy release, with roof displacement accelerating markedly after the main horizon failed. We therefore propose two dimensionless indices—the dynamic load factor (DLF) and stress concentration factor (SCF)—to characterize burst severity; peak values reached 1.62 and 2.43, respectively, while pronounced stress accumulation was localized 6–15 m ahead of the face. These metrics furnish a theoretical basis for early warning systems and control strategies aimed at intense rock burst.

When mineral deposits are mined using underground methods, rock burst hazards arise as the depth increases. The experience of developing such deposits shows that when mining operations reach ‘critical depths,’ technological processes begin to be accompanied by sudden failures of the ore and rock masses in the most dangerous dynamic forms, i.e. as the rock bursts and bumps as well as tectonic shocks. This paper presents the results of assessing the geomechanical condition of the Krasivoe deposit to ensure safe mining operations and prevent dynamic manifestations of the rock pressure. This gold deposit is located in the north-western part of the Ayano-Maisky administrative district of the Khabarovsk Territory, and its reserves are currently mined almost completely out to the level of +850 m (the depth of 350 m). In the near and medium term, it is planned to develop the reserves in the bottom part of the deposit to the level of +615 m (the depth of 585 m from the surface). Based on a combination of factors and the results of comprehensive studies, as well as data from field observations and instrumental measurements in the mine workings, the Krasivoe deposit needs to be classified as prone to rock bursts below the depth of 350 m (+850 m level).