Search Results (108)

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. Full article

Coal-rock dynamic disasters, especially rock bursts, require insight into the spatiotemporal evolution of strain and temperature to clarify failure mechanisms and improve early warning. This study aims to characterize the spatiotemporal evolution of the strain field during brittle rock instability by developing a multi-point Fiber Bragg Grating (FBG) strain–temperature monitoring and inversion method. Multi-directional, multi-location FBG deployment enables real-time reconstruction of strain tensors and temperature at each monitoring point, capturing both surface and internal responses under loading. The strain records resolve four stages—initial smoothing, linear growth, pre-peak nonlinearity, and failure fluctuation—with earlier sensitivity than Linear Variable Differential Transformers (LVDT), enabling finer localization of yielding and microcracking. The FBG sensors capture clear spatial heterogeneity and timing offsets during yielding, supporting instability warning. Temperature results show a slow rise followed by a surge from the end of the elastic stage into the plastic stage, reaching ~1.6 °C before declining; the thermal peak precedes the stress peak by ~0.38 s. Meanwhile, the temperature-field coefficient of variation jumps from <0.15 to >0.25, indicating a transition from diffuse heating to banded localization. Together, these strain–temperature precursors validate the FBG-based method as an effective and reliable approach for early warning of brittle rock instability. Full article

Rock bursts usually happen during the hours or days after tunnel excavation, even in an unsupported opening where no collapses occur. To investigate the mechanism of those delayed failures in brittle rock tunnels, this paper showcases the performed scale-model test based upon the Jinping II headrace tunnelling project. The model test was conducted in a particularly designed loading apparatus; the scale-model is composed of a similar material for the deep brittle rock. The tunnel in the scale-model is excavated by a specially made drilling tool. The failure mode of the deep circle tunnel under isotropic and anisotropic geostress were obtained; the delay failure time was recorded, and the accompanying stresses and strains changing were monitored. Under isotropic geostress the failure shape has a smooth circle boundary, failure process totally costs 56 h. While under anisotropic geostress a dog-eared breakdown was found, the failure process amounted to 72 h. The time-to-failure was evaluated by delay failure theory, and the evaluation equation was implemented into in FEM code. Numerical simulations have been performed to simulate the failure time and failure mode. The numerical results of failure time and failure mode mainly match the scale-model testing results. Full article

To address roof overhang hazards (e.g., rock bursts and gas accumulation) in high-gas coal mines, this study proposes a static stress intervention method for controlled directional roof collapse. Using the 150110 fully mechanized face at Yiyuan Coal Mine as a case study, we investigate the mechanical mechanism of static stress intervention-induced roof collapse through theoretical modeling and FLAC3D simulations in the absence of pre-cracks. The study reveals that advanced boreholes filled with static expansion agents generate stress concentration zones along the drilling array. When superimposed with mining-induced stresses, this configuration induces tensile failure preferentially at borehole locations, thereby achieving controlled directional roof collapse. Theoretical calculations indicate that roof fracturing occurs at predetermined locations when expansion pressure reaches ≥9.11 MPa. FLAC3D simulations analyzed stress redistribution and plastic zone evolution under combined static and mining-induced stresses, demonstrating the method’s efficacy in optimizing roadway stability. Field trials implement spaced boreholes (65 mm diameter, 16 m depth, 1 m spacing) with alternating expansion agent charging, achieving a 6 m reduction in roof collapse intervals, effectively mitigating overhang hazards. Results confirm that static stress intervention reshapes the roof stress field, inducing tensile failure along predetermined paths without relying on pre-cracks. The findings provide theoretical and technical insights for roof stability control in high-gas coal mines. Full article

During deep mining engineering, coal bodies are subjected to complex geological stresses such as periodic roof pressure and blasting impacts, which may induce mechanical property deterioration and trigger severe rock burst accidents. This study systematically investigated the mechanical characteristics and failure mechanisms of coal under strain rates on two orders of magnitude through quasi-static cyclic loading–unloading experiments and split Hopkinson pressure bar (SHPB) tests, combined with acoustic emission (AE) localization and crack characteristic stress analysis. The research focused on the differential mechanical responses of coal-rock masses under distinct stress environments in deep mining. The results demonstrated that under quasi-static loading, the stress–strain curve exhibited four characteristic stages: compaction (I), linear elasticity (II), nonlinear crack propagation (III), and post-peak softening (IV). The peak strain displayed linear growth with increasing cycle, accompanied by a failure mode characterized by oblique shear failure that induced a transition from gradual to abrupt increases in the AE counts. In contrast, under the dynamic loading conditions, there was a bifurcated post-peak phase consisting of two unloading stages due to elastic rebound effects, with nonlinear growth of the peak strain and an interlaced failure pattern combining lateral tensile cracks and axial compressive fractures. The two loading conditions exhibited similar evolutionary trends in crack damage stress, though a slight reduction in stress occurred during the final dynamic loading phase due to accumulated damage. Notably, the crack closure stress under quasi-static loading followed a decrease–increase pattern with cycle progression, whereas the dynamic loading conditions presented the inverse increase–decrease tendency. These findings provide theoretical foundations for stability control in underground engineering and prevention of dynamic hazards. Full article

During coal resource mining, hard roof mining is prone to causing rock-burst disasters because traditional blasting–cutting roof technology has the disadvantages of low efficiency and high cost. This article studies the theoretical basis and engineering application of fracturing technology with a static expansion agent (SCA). The influences of borehole diameter and spacing on the fracturing effect of a rock mass are studied through theoretical analysis and simulation. Rock mass models of a cantilever beam for a single rock layer and multiple layers were established, and the mechanical properties of the roof strata under three working conditions were analyzed. The research results show that the maximum annular stress value occurs along the drill hole wall between the adjacent drill holes, and the annular stress at the center line between two drill holes is the smallest. As the spacing between the holes increases, the annular stress at the center line decreases; however, the annular stress at the center of the drill line becomes larger with the increase in hole diameter. The degree of stress concentration increases sharply with the decrease in distance f from the borehole center to the free surface. Relative to the cantilever beam model of a single rock layer, the combined rock layers can effectively control the displacement and deformation of the cantilever roof. Based on the above research results, a drilling method with a 75 mm diameter and a 10° inclination angle is used, demonstrating that the suspended roof area can be reduced to below 20 m² using the fracturing technology with a static expansion agent, allowing the roof strata to fall simultaneously during mining. Full article

Based on considering the stress state distribution and potential failure surface of the specimen during uniaxial compression, the drilling parameters (layout, spacing, position) are set. Thoroughly understanding the influence of different drilling parameters on the pressure relief effect is conducive to reducing the occurrence of coal mine rock burst accidents. Through laboratory tests and numerical simulation tests under different drilling parameters, the influence laws of mechanical parameters, failure characteristics, AE characteristic parameters and energy evolution of specimens under different drilling parameters were studied. The pressure relief effect under different drilling parameters was evaluated by using the pressure relief effect evaluation index (X), and the best combination of drilling parameters was obtained. The results show the following: (1) Compared with the intact specimen, the peak strength of the drilling specimen is significantly reduced, and the drilling layout has the greatest influence on the mechanical properties, followed by the drilling spacing and drilling position. (2) Different drilling layouts will form different weak-strength surfaces in the specimen, and lead the expansion and penetration of cracks, resulting in different failure modes of the specimen. The stress distribution inside the specimen will affect the stress concentration around the borehole, finally affect the damage degree of the specimen. (3) Drilling can not only effectively reduce the energy accumulation capacity, but also enhance the degree of energy dissipation. The AE ringing counts and energy of the triangular-drilling specimens are the least. The AE ringing counts and energy decrease first and then increase with the increase in drilling spacing, and are the smallest at three times the drilling diameter. The AE ringing counts and energy increase gradually with the upward movement of the drilling position. (4) The optimal combination of drilling parameters was obtained by the test, and it was triangular-layout drilling, drilling spacing three times the diameter, and the drilling position in the middle of the specimen, and the value of the pressure relief effect evaluation index (X) was 65.41. The research results can provide some reference for the selection and optimization of drilling pressure relief parameters in rock burst mines. Full article

To study the influence of the main roof period pressure on the instability mechanism of rock pillars with burst liability, the composite loading mode of “pre-cycling loading + continuous loading with a constant rate” was used to conduct compression experiments on rock samples. Meanwhile, the mechanical behaviour response characteristics of rock samples were discussed. Experiment results are shown as follows: (1) mechanical properties of rock samples were strengthened by closing primary pores under pre-cycling loading. The surface roughness and secondary crack number decreased gradually with the pre-cycling threshold; (2) the Kaiser effect of AE (Acoustic Emission) signals was significant in the second and third pre-cycling loading and unloading stages. The Kaiser effect disappeared in the continuous loading stage; (3) AF-RA (Average Frequency-Risetime Amplitude) signals were distributed in a dense-sparse-dense form. Low AF and high RA shear type cracks were more common. Shear failure was the dominant failure mode in rock samples. Full article

Parallelepipeds specimens were made to further investigate the rockburst occurrence mechanism of ore pillars in underground mining units. The investigation was carried out with uniaxial compression systems and real-time testing systems, such as stress, video, and acoustic emission, combined with digital image correlation (DIC) and SEM electron microscope scanning technology, to systematically analyze the evolution of rockburst of ore pillars, strain field characteristics, acoustic emission characteristics, mesoscopic characteristics of the rockburst fracture, morphology of the bursting crater, and debris characteristics. The findings demonstrate that the pillar’s rockburst process went through four stages, including the calm period, the particle ejection period, the block spalling period, and the full collapse period. According to DIC digital image correlation technology, the development of cracks in the rock is not obvious during the calm period, but during the small particle ejection and block spalling periods, the microcracks started to form and expand more quickly and eventually reached the critical surface of the rock, resulting in the formation of a complete macro-rockburst rupture zone. During stage I of the test, the rate of acoustic emission events and energy was relatively low; from stages II to IV, the rate gradually increased; and in stage V, the rate of acoustic emission events and energy reached its maximum value at the precise moment the rock exploded, releasing all of its stored energy. The specimen pit section primarily exhibits shear damage and the fracture exhibits shear fracture morphology, while the ejecta body primarily exhibits tensile damage and the fracture exhibits tensile fracture morphology. The location of the explosion pit is distributed on the left and right sides of the middle pillar of the specimen, and the shape is a deep “V”. The majority of the rockburst debris is greater than 5 mm, and it mostly takes the shape of thin plates, which is comparable to the field rockburst debris’s shape features. Full article

In view of the high-level, thick, and hard roof in a mine in Shaanxi, it is difficult for existing technology to solve the problem of frequent rock bursts, which are caused by the direct weakening of the whole underground layer. In this paper, a technology for preventing rock bursts using the long-distance drilling and blasting of a thick and hard roof in a high drilling field is proposed. The authors used theoretical analyses, numerical simulations, and other research methods to analyze the mechanisms of pressure relief and load reduction achieved by this technology, determined its layout parameters and layers, and carried out engineering practices in 2412 working faces in a mine in Shaanxi. The results show that the long-distance drilling and blasting technology can achieve the aim of unloading the pressure drop load by arranging a high-level drilling field to achieve the whole-layer presplitting of the thick and hard roof above the working face. According to the orthogonal test method, when using long-distance drilling and blasting under the condition of a high-level roof, the choice of the blasting layer is the biggest factor affecting the change in overburden subsidence. Using the identification basis of the main control disaster causing the layer of overburden, it was determined that 52~67 m above the coal seam of the 2412 working faces was the blasting layer. According to the periodic weighting interval of the working face and the development radius of the fractures in the blasting surrounding rock, the blast hole spacing was determined to be 30 m. After long-distance drilling and blasting, the frequency and energy of micro seismic events were reduced, the entry deformation was reduced compared with the common roof deep-hole blasting technology, and the pressure relief effect of the long-distance drilling and blasting technology was better. These research conclusions can provide theoretical support for the prevention and control of rock bursts during mining production under similar conditions by reducing the load and the unloading pressure on thick and hard roof layers that are difficult to unload from the source. Full article

The phenomenon of crushing the support of the hard roof of a coal seam occurs occasionally during the coal mining process. However, making the hard roof fall is difficult due to its good integrity and high strength. A vast area of unsupported, suspended roof can easily form in the goaf, inducing the hidden dangers of rock burst and coal and gas outbursts. A deep-hole pre-splitting blasting technique is used to fracture the roof and relieve the pressure exerted by the rigid roof in order to improve the caving of the hard roof and protect the stability of the roadway, ensuring safe and effective operational production of the 1127 (1) working face in Guqiao Coal Mine. By collecting field samples, the mechanical properties of relevant rock formations are ascertained. Combining numerical simulation with theoretical computation, a roof cutting pressure-relief scheme with a roof cutting height of 13.5 m and a roof cutting angle of 20° is selected. This scheme can decrease the peak vertical stress on the roadway roof from 22.01 MPa to 13.63 MPa compared to when roof cutting is not performed. By ensuring the effectiveness of roof cutting for pressure relief, this scheme can optimize the actual construction workload to a minimum. The study’s conclusions provide insightful information and can be used as a guide for future research on related technical topics. Full article

The environmental damage and mining accidents caused by water inrush accidents and rock burst are two major problems faced in the safe and sustainable deep mining of extremely thick weakly cemented overlying strata. Mastering the fracture development law of the overlying strata, the evolution characteristics of high-energy events, and their correlative relationships in the deep mining of extremely thick weakly cemented overlying strata is the key to solving the above two problems, which is directly related to the sustainable development of regional coal and the protection of underground water resources in mining areas. By integrating the geological characteristics of extremely thick and weakly cemented overburdens in the Shaanxi–Inner Mongolia mining region of China, this study adopts methods such as field measurements, numerical simulations, and theoretical analyses to investigate the energy evolution characteristics of regional mining-induced tremors, as well as the correlation and mutual influence mechanisms between overburden fracture development and high-energy events. The results indicate a positive correlation between high-energy events and the development height of overburden fractures, suggesting that the occurrence of high-energy events can increase the height of overburden fracture development. Furthermore, high-energy events occurring before and after the “parallel joining” of two working faces have a relatively minor impact on the development height of overburden fractures, with an increase in the fracture-to-mining ratio (FMR) ranging from 1.56 to 2.78. In contrast, high-energy events occurring during the “parallel joining” of two working faces significantly affect the development height of overburden fractures, resulting in an FMR increase of 10.33 to 13.44, approximately one-third of the FMR measured through boreholes. The research results can provide a scientific basis for the safe and sustainable coal mining and the protection of underground water resources in similar mining areas with extremely thick weakly cemented overlying strata. Full article

Decreasing the rockburst potential in longwall mining of burst-prone coal seams has been a longstanding challenge for geotechnical engineering worldwide. One of the effective approaches is drilling of relief boreholes in front of the coal seam face from the airways. This work presents a novel approach based on the integral rockburst factor ($K_{Irb}$) taking account of the length of the dynamic abutment stress influence zone and the ratio of the vertical stress to the remote field virgin stress. The geotechnical conditions of seam 3 of the Alardinskaya mine (Kuznetsky basin, Russia) are taken as a study site. An approach of the finite-difference continuum damage mechanics is employed to describe the processes of deformation and fracture of coal and host rocks using an in-house software. The results indicate that the abutment stress maximum shifts deep into the seam after drilling and that the stress distribution along the coal seam horizon is a superposition of the solutions similar to those of the elastoplastic Kirsch problem. The results also indicate that the curves of $K_{Irb}$ dependence on spacing between the boreholes and their diameter are nonlinear and non-monotonic functions, which allows for optimizing of the drilling technology. Full article

The stress environments of gob-side roadways (GSRs) are becoming increasingly complex during deep coal mining under thick and hard roofs. This leads to strong strata behaviors, including roadway floor heave, roof subsidence, and even coal bursts. Among them, coal bursts pose the greatest threat to production safety in coal mines. Coal bursts in a GSR strongly correlate with the load characteristics and stress-energy evolution laws of the roadway. This study analyzes the roof structures of double working faces (DWFs) during the initial weighting stage (IWS) and full mining stage (FMS) of gob-side working faces (GSWFs). This study also explores how varying roof structures affect the stability of GSRs. Three-dimensional roof structure models of DWFs and mechanical models of dynamic and static loads superposition on a GSR throughout the IWS and FMS of a GSWF were developed. An analysis identified the primary stress sources affecting the GSR throughout various mining stages of the GSWF. Subsequently, the principle of “three-load” superposition was developed. A novel method was proposed to quantify the stress state in the GSR surrounding rock across different mining stages of the GSWF. The method quantitatively characterizes the load of the GSR surrounding rock. Based on this, the criterion for judging the burst failure of the roadway was established. Numerical simulations are used to analyze the stress-energy evolution laws of the working face, coal pillar, and GSR surrounding rock during the mining process of the GSWF. These findings offer valuable references for studying and preventing coal bursts in GSRs under equivalent geological situations. Full article

Rock bursts are among the most severe and unpredictable hazards encountered in deep rock engineering, posing substantial threats to both construction safety and project progress. This study provides a comprehensive investigation into how moisture infiltration influences the propensity for rock bursts, aiming to establish new theoretical foundations and practical methods for their prevention. Through the analysis of meticulous laboratory mechanical experiments and sophisticated numerical simulations, we analyzed the variations in the physical and mechanical properties of rocks under different moisture conditions, with a particular focus on strength, brittleness, and energy release characteristics. The findings reveal that moisture infiltration significantly diminishes rock strength and reduces the likelihood of brittle fractures, thereby effectively mitigating the risk of rock bursts. Additionally, further research indicates that in high-moisture environments, the marked reduction in rock burst tendency is attributed to increased rock toughness and the suppression of crack propagation. This study advocates for the implementation of moisture control measures as a pre-treatment strategy for deep rock masses. This innovative approach presents a viable and effective solution to enhance engineering safety and improve construction efficiency, offering a practical method for managing rock burst risks in challenging environments. Full article