Coal Seam Mining Research Articles

Microseismic monitoring energy and GHG emission correlation assessment of extremely thick coal seam mining in China

Microseismic monitoring energy and GHG emission correlation assessment of extremely thick coal seam mining in China

Research on the occurrence mechanism of mine earthquake in Longwanggou Coal Mine and its damage assessment to surface buildings

The mining of extra-thick coal seams is prone to triggering mine earthquake, which causes damage to surface buildings and severely restricts the sustainable development of coal mines. This study constructs a spatial structural model of hard rock tearing-type fracture at the 61,607 working face in Longwanggou Coal Mine. Through analytical modeling of stress-energy characteristics during fracture propagation, we quantitatively estimate the vibrational energy partitioning within rock mass discontinuities and evaluate the maximum potential magnitude (ML) of mine earthquake. Critical kinematic parameters, including peak ground acceleration (PGA) and particle velocity (PGV), are extracted to systematically evaluate vibration-induced damage to surface structures, with data sourced from seismic waveforms. The results indicate that the maximum magnitude estimated by the calculation model for hard rock tearing-type mine earthquake is in close agreement with on-site monitoring results, exhibiting a deviation of approximately 14%. The peak values of the acceleration response spectrum for seismic signals are concentrated in the 0.1–0.5 s range, where the bottom frames of buildings with natural vibration periods close to this interval are affected to a certain extent but exhibit lower vibration intensity than that induced by natural earthquakes. The attenuation of mine earthquake vibrations adheres to a power-law exponential pattern, with PGA decaying to an extremely low level at kilometer-scale distances. Additionally, the velocity response of mine dormitories meets relevant safety standards, collectively indicating that mine earthquake exerts essentially no substantial impact on the structural integrity of surface buildings.

Experimental-simulation analysis on mechanical degradation and energy evolution characteristics of sandstone under water-rock coupling effects

With increasing coal mining depths, water-rock interactions exacerbate the mechanical degradation of coal-rock masses and geological disaster risks. Investigating the mechanical properties and energy evolution mechanisms of water-bearing sandstone is crucial for ensuring safe mining operations. To address the existing research gap in analyzing energy evolution mechanisms of water-saturated rock masses from a macroscopic perspective and the lack of exploration into energy mechanisms at critical failure points at the mesoscale, this study employs the particle discrete element software PFC3D to establish numerical models of sandstone with varying water contents. Combined with uniaxial compression tests and energy calculation principles, the mechanical degradation laws and energy evolution characteristics of sandstone under water-rock interactions are systematically investigated. The results indicate that the mechanical properties of sandstone exhibit significant degradation with prolonged immersion time, where compressive strength and elastic modulus gradually decrease with increasing water content. Energy evolution during sandstone deformation and failure can be divided into three stages: elastic energy storage, crack propagation energy dissipation, and sudden energy release at failure. Water immersion significantly reduces energy absorption efficiency during the elastic storage stage and increases energy dissipation rates during crack propagation. Mesoscale crack development analysis reveals that water accelerates the extension of initial fractures and the initiation of new cracks, while higher water content promotes a transition from localized to diffuse crack distribution. Additionally, the energy thresholds at critical failure points and failure modes of samples with different water contents show significant correlations, revealing the dynamic regulatory mechanism of water-induced weakening effects on energy accumulation and release in sandstone. These findings provide theoretical support for safe mining and dynamic disaster prevention in deep water-rich coal seams.

Water Inrush Mechanism During Mining Adjacent to Large Water-Conducting Faults

In mining operations, the rock mass located between the water-conducting fault fracture zone and the waterproof protective coal column is highly susceptible to damage, which may result in sudden water inrush disasters. This paper first employs indoor experiments and on-site rock sample analysis to determine the macroscopic mechanical parameters of rocks and rock masses, as well as the microscopic mechanical parameters of block contacts. The fracture and seepage evolution mechanisms in the mining-induced rock mass adjacent to major faults were analyzed utilizing the discrete element-fluid coupling theory in Universal Distinct Element Code (UDEC). The results identified three primary pathways for water hazards caused by mining: the calculated stress field and seepage field indicated that the formation of the water-inrush channels was determined by the parameters of coal seam mining. Different waterproof protective coal columns were set up for the three geological conditions under study. Additionally, a “claw-shaped” detection and flow monitoring method has been proposed for small water-conducting faults. These findings are important and provide valuable guidance for understanding and managing water inrush hazards in mining operations near major faults.

Study on mine pressure law and support resistance of working face under shallow buried gully terrain

Because of the control problems caused by the non-uniform load of the roof of the working face when the shallow coal seam is mined under the condition of gully terrain. In this study, theoretical analysis, similar simulation, and field measurement methods are comprehensively used to incorporate gully topographic factors into the study of roof structure control, and a mechanical model of roof structure under non-uniform load is constructed. The interaction relationship between “powered roof support-rock mass” during the period of periodic pressure is analyzed, the corresponding model is established, and then the calculation equation of support resistance for controlling the sliding instability of the roof structure passing through the gully is derived. Taking the first mining face of Shaliang Coal Mine as the engineering background, reasonable support resistance is given based on the above research results. Through similar simulation experiments, the average weighting steps in the mining stage of downhill, gully bottom, uphill, and convex landforms are 19 m, 30 m, 14 m, and 15 m, respectively. The periodic weighting step in the gully bottom stage is the largest and the uphill mining stage is the shortest. Verified by field measured data, the derived equation is accurate and reliable. The research results enrich the roof control theory of shallow coal seam mining, provide key technical support and practical guidance for coal mining under similar geological conditions, and help to ensure coal mine safety production.

Monitoring method for borehole images of changes in overlying rock structure during coal mining

The migration of overlying rock layers caused by underground coal seam mining is the root cause of all mining pressure manifestations in the mining area. In order to visually record the changes in the overlying rock structure during coal seam mining, this paper proposes a borehole image monitoring method suitable for monitoring the changes in the overlying rock structure during coal seam mining. Firstly, based on the characteristics of rock structure borehole images collected in actual borehole environments, a preprocessing method for rock structure borehole images that can weaken the brightness and darkness features caused by lighting intensity is constructed to improve the recognition ability of borehole images. Subsequently, in response to the complexity and uncertainty of changes in the overlying rock mass structure, a method for locating the characteristic areas of rock mass structure is proposed to achieve the localization of structural characteristic areas at different times. Finally, a three state expression method is constructed to achieve dynamic tracking of the evolution process of rock mass structure. At the same time, combined with practical case analysis, the feasibility and correctness of the method proposed in this paper have been verified. This study not only contributions to to deepen the understanding of the evolution process and laws of the overlying rock mass structure, improve the ability of coal mine disaster prevention and control, but also provides useful references and guidance for the further development and application of coal mine video surveillance technology.

Gas flow patterns in goaf and optimization of spatial parameters for directional borehole in deep thick coal seam mining

To address the complex gas flow and significant gas disaster threats in the goaf of deep thick coal seam mining, this study investigates the gas flow patterns and optimizes the spatial parameters for roof directional borehole in the goaf. By combining particle flow code and COMSOL numerical simulations, the study analyzes the stress-permeability evolution in the goaf and the gas migration patterns. The results reveal a strong correlation between the permeability of the goaf and the stress distribution, showing distinct zonal characteristics. The permeability decreases slowly in the coal wall-supported separation zone, drops rapidly in the transition zone, and stabilizes in the compaction zone. Without gas extraction, the gas concentration in the goaf can exceed 40% at 100 m from the working face and surpass 70% in the deepest parts. Additionally, gas accumulation at the upper corner can exceed 0.6%. The optimal spatial parameters for roof directional boreholes were determined as a 25 m from the return airway, a vertical height of 25–35 m, a horizontal spacing of 6 m, and an extraction pressure of 20 kPa. Field implementation confirmed that these parameters significantly improve gas extraction effect and reduce gas concentrations in the upper corner of the return airway, providing a reliable reference for gas control in similar mining conditions.

Numerical simulation of plant lateral root stress perturbation during shallow coal seam mining in the semi-arid region of Western China

Numerical simulation of plant lateral root stress perturbation during shallow coal seam mining in the semi-arid region of Western China

Study on the Formation and Evolution of Constant Stress Concentration Shell in Overburden Rock Strata During Coal Seam Mining

Study on the Formation and Evolution of Constant Stress Concentration Shell in Overburden Rock Strata During Coal Seam Mining

Experimental Study on Aerodynamic Stimulation Technology of Gas Surface Pumping Well

The existing underground extraction methods have limitations and timeliness. The cost of mine outburst prevention and gas drainage is high, and the rate of gas drainage is low. The combination of gas surface extraction technology and underground gas extraction can effectively improve the effect of underground gas control. Aerodynamic surging technology is an important completion antireflection and outburst elimination technology for surface gas drainage wells. In Weijiadi Coal Mine, the application of aerodynamic oscillation cavitation technology to mine outburst prevention is one of the methods of cave completion. Through rapid gas pressure fluctuation, the reservoir produces stress damage, which leads to wellbore collapse, increases the exposed area of the reservoir, and destroys the coal seam blocked by the mud pollution channel around the wellbore. Through the suppression and discharge of high gas pressure, the blockage in the coal seam gap-coal ash can be poured into the wellbore, resulting in several self-supporting cracks extending in all directions, so as to realize the effective connection between the wellbore and the reservoir. Through the aerodynamic stimulation technology of the coal seam in the test well, the permeability of the plastic failure area is effectively increased, the efficient extraction of gas near the workload is realized, and the safety hazards of coal seam mining are eliminated in advance. It provides theoretical and practical support for the efficient development of coalbed methane and gas ground treatment, and has important engineering practical significance.

Experimental study on damage law of coal seam under hydraulic fracturing and blast load

Compared with blast mining only, blast mining after on-site hydraulic fracturing can make the mining easier and obtain better mining outcomes. To explore the effects of hydraulic fracturing on the blasting damages in coal seam, blasting experiments were carried out under biaxial confining pressure using the synthetic coal briquettes. The coal briquettes with the same mechanical properties as coal seam were prepared and the mica sheets with different radii and thicknesses were added to simulate the internal hydraulic fractures of different radii and openings. The internal damage distributions and stress attenuations of the coal briquette specimens with different hydraulic fracture radii and openings after the blasting were then measured using a rock ultrasonic tester and a static-dynamic strainmeter. Based on the rock blasting theory, the effects of hydraulic fractures with different radii and openings on the blast fracture propagation and coal seam damage were analyzed. The following conclusions are drawn: (1) The increases in hydraulic fracture radius mainly enhance the damages in the vertical direction to the hydraulic fracture, and can increase the vertical range of the severely damaged area by 20–25 cm. The increases in the hydraulic fracture opening mainly cause more severe damages along the direction of the hydraulic fracture and increase the horizontal range of the severely damaged area by 30 cm. (2) The area of the severely damaged area caused by blasting increases by 550 cm2 as the hydraulic fracture radius increased from 5 to 15 cm. As the hydraulic fracture opening increased from 2 to 10 mm, and the area of the severely damaged area caused by blasting increases by 650 cm2. Therefore, the hydraulic fracture opening has greater impacts on the severely damaged area. (3) The increase in the hydraulic fracture length reduces the compression phase attenuation of the blast stress in the radial direction. Both the increases of the hydraulic fracture length and opening increase the absolute value of the tensile phase in the radial direction. (4) Increasing the hydraulic fracture radius and opening can greatly promote the development of blast fractures and enhance the damages to coal seam. Therefore, the coal seam mining effect can be improved by increasing the radii or openings of hydraulic fractures to adjust the main action direction of blast fracture.

Failure Characteristics and Control Strategies of Overlying Remaining Coal Pillars in Close-Distance Coal Seam Mining

Failure Characteristics and Control Strategies of Overlying Remaining Coal Pillars in Close-Distance Coal Seam Mining

Mechanism of Mining-Induced Dynamic Loading in Shallow Coal Seams Crossing Maoliang Terrain

To address the intense mining pressure and dynamic accidents, such as shield collapse during mining in shallow coal seams crossing the Maoliang terrain, this study focuses on Panel 30206 of the Yanghuopan Coal Mine. Through theoretical analysis, numerical simulation, and field measurements, the stress transfer patterns and dynamic changes in shield loads during mining were analyzed, and the mechanism of dynamic mining pressure and calculation method for maximum support resistance were determined. The results show that when the working face enters the load-affected zone of the Maoliang terrain, the base load ratio of the overburden increases. The fracturing of the roof strata causes a synchronized motion between the key stratum and the overlying surface layer. The fracture and instability of the key stratum under mining-induced terrain loads significantly increase the shield resistance and intensify the mining pressure, with a hysteresis effect. Field measurements indicate a maximum shield working resistance of 8974 kN at Panel 30206, showing a 3.25% deviation from the theoretical value of 9266 kN, with a 25 m lag behind the peak load in the Maoliang terrain. This research provides criteria for support selection and ground control in Maoliang terrain mining, ensuring safe production.

Theory and numerical simulation study on the plastic slip failure mechanism of multi-layered coal seam Floors-A case analysis

Coal seam mining induces disturbances in underground floors, leading to plastic failure, which presents significant safety risks, particularly in areas with underlying pressurized water. Accurately assessing the maximum depth of such floor failure is crucial for ensuring safe mining operations. This study investigates the evolution of apparent resistivity in the floor of the 4,301 working face using the network parallel electrical method. The observed maximum failure depth was found to be 19.3 m. Based on these measurements, the plastic slip theory for a homogeneous rock layer was applied, incorporating mining parameters such as burial depth and mining height. Five mechanical models for plastic slip failure in multi-layer composite floors were developed, with the maximum failure depth calculated to be 18.26 m. The study also explores the impact of factors such as mining height, burial depth, and the internal friction angle of the rock layers on floor failure depth. The results demonstrate that multi-layer composite floors exhibit a 23.1% reduction in failure depth on average compared to homogeneous floors. Numerical simulations confirmed that the maximum failure depth under mining disturbance is 19.2 m, with shear failure identified as the predominant failure mode. The findings from the theoretical analysis, numerical simulations, and field measurements align closely, validating the applicability of the plastic slip theory for multi-layer composite floors. This research provides critical theoretical support for safe mining operations in coal seams above confined aquifers and effective water control strategies.

Prediction of Water Inrush Hazard in Fully Mechanized Coal Seams’ Mining Under Aquifers by Numerical Simulation in ANSYS Software

The process of fully mechanized coal seam mining under aquifers and surface water bodies has been a challenge in recent years for different countries. During the evolution of subsidence and the overburdening of rock mass movement above the longwall goaf, there is always a potential risk of connecting the water-conducting fracture zone with aquifers. The water inflows in the coal mine’s roadways have a negative impact on the productivity of the working faces and pose significant hazards to miners in the event of water inrush. Therefore, the assessment of the height of the water-flowing fractured zone has an important scientific and practical significance. The background of this study is the Xinhu Coal Mine in Anhui Province, China. In the number 81 mining area of the Xinhu Coal Mine during the mining of the number 815 longwall, a water inflow occurred due to fractures in the sandstone in the overburden rock. The experience of the successful implementation of the water inrush control method by horizontal regional grouting through multiple directional wells is described in this paper. This study proposes an algorithm for the assessment of the risk of water inrush from aquifers, based on an ANSYS 17.2 simulation in the complex anticline coal seam bedding. It was found that the safety factors based on the stress and strain parameters can be used as criteria for the risk of rock failure in the aquifer zone. For the number 817 longwall panel of the Xinhu Coal Mine, the probability of rock mass failure indicates a low risk of the occurrence of a water-flowing fractured zone.

Study on the instability characteristics and influencing mechanism of coal-rock parting-coal structure under triaxial loading

Rockburst accidents are highly likely to take place during the mining of coal seams in bifurcated area. A conventional triaxial testing machine and an acoustic emission (AE) monitoring system are employed to investigate the failure and instability characteristics of coal-rock parting-coal structure (CRCS) and its influencing mechanism. The results show that: (1) The instability process of the composite structure under the conventional triaxial path represents a coupled instability process of contact surface slipping and coal/rock fracture. The penetration of tensile fractures into shear fractures serves as the primary cause of the overall instability of the composite structure. (2) Alterations in the main frequency and maximum amplitude, a sharp decrease in the radiant energy index, and a significant increase in the cumulative apparent volume can be utilized as precursor identification information of the slipping and overall instability of the composite structure. (3) The inclination angle of the contact surface, confining pressure, and loading speed have an impact on the instability of the composite structure. Effectively controlling these factors during production can contribute to reducing the risk of impact disasters. The research results can provide theoretical support for the early warning and prevention of rockburst accidents in the bifurcated area.

Research on the optimization of optimal blasting parameters and fragmentation control based on coal seam geological conditions

Open-pit coal mining often employs loosening blasting, with perforation blasting accounting for a significant portion of the coal seam mining costs. For coal of the same quality, the price of lump coal is much higher than that of crushed coal. Therefore, reducing the percentage of crushed coal in the blasting process is an important means to improve quality and efficiency in open-pit coal mining. How to develop a reasonable blasting scheme based on actual geological conditions has been a hot topic among scholars. In response to this issue, this study combines numerical simulation and field tests. Using the LS-DYNA software’s fluid–solid coupling algorithm, the effects of charge structure, explosive type, intermediate medium, and hole spacing parameters on blasting results are analyzed. An optimized blasting scheme is determined, with specific parameters including a charge spacing of 7 m, hole spacing of 11 m, charge structure with a 5 m blocking length, 4 m upper charge length, 2 m intermediate coal powder spacing, and 5 m lower charge length, using low-density explosives. This optimized scheme is applied in field tests, and a comparison with the control group shows that the fines rate decreased from 30.10 to 24.17%, a reduction of 5.93%; the lump coal proportion increased from 59.33 to 68.41%, an increase of 9.08%; and the proportion of large coal lumps decreased from 10.57 to 7.42%, a decrease of 3.15%. The fines rate and large lump rate decreased in the experimental group compared to the control group, improving blasting efficiency and effectively reducing the downtime of the surface production system due to blockages. This study not only provides theoretical guidance for blasting in soft coal seams of open-pit coal mines but also offers scientific support for practical engineering applications, demonstrating significant engineering value and broad application prospects.

Investigating fracture evolution mechanisms in thick coal seam mining under upper hard and lower soft overburden: a case study

To investigate the fracture evolution mechanisms during thick coal seam mining under an upper hard-lower soft overburden structure, this study analyzed the 304 working face of the Tingnan coal mine in the Binchang mining area. A physical similarity model (1.20 m height, 1:250 geometric similarity ratio) was constructed to simulate overburden fracture propagation, complemented by numerical simulations using FLAC3D and theoretical analysis based on linear elastic fracture mechanics and Griffith’s energy release rate criterion. Results indicate that in soft rock layers, fractures propagate at an average inclination of 70°, while in hard rock, they extend more steeply, reaching 80°. The height of the water-conducting fracture zone was measured at 266.4 m in physical experiments, whereas theoretical analysis predicted 225.53 m, with a relative deviation of 15.3%. Stress analysis revealed that fracture initiation followed the maximum circumferential stress criterion, exhibiting compressive-shear failure characteristics. These findings enhance the accuracy of overburden fracture height predictions and provide theoretical support for mitigating water inrush hazards in thick coal seam mining.

Crack evolution and energy conversion characteristics of coal under acid corrosion conditions

In the process of coal mining with complex hydrological conditions, underground coal seams are often subjected to corrosion by acidic water, and acidic water–rock chemical interactions can significantly affect the mechanical properties of coal rocks, posing challenges for mine tunnel support and coal seam stability. This study investigates the effects of acidic solution exposure, specifically varying pH levels, on the mechanical and structural properties of coal samples. Static Brazilian splitting tests were conducted to determine the tensile mechanical properties of the treated coal samples. Additionally, the Particle Flow Code (PFC) was utilized to examine the evolution of microcracks, stress fields, and energy conversion characteristics within the coal samples. The results indicate that acidic solutions induce damage and softening of the coal structure, leading to a reduction in tensile strength and elastic modulus as acid corrosion intensifies. The primary mechanism of failure in the coal samples is attributed to the initiation, propagation, nucleation, and rapid consolidation of microcracks within stress concentration zones. A decrease in the area of stress concentration zones, increased stress unevenness, and reduced ultimate tensile strength in corroded coal samples lead to more complex crack propagation paths and lower macroscopic strength. Energy monitoring further reveals that acid-corroded coal has reduced resistance to damage and higher failure rates, highlighting the heightened vulnerability of acid-affected coal in structural applications.

Study of the influence of coal column width on the stress-fracture-displacement evolution law in sequential coal seam mining

The connectivity of the fissures in the adjacent air section represents a crucial foundation for the deployment of surface gas extraction drill holes in abandoned mines. To elucidate the impact of coal column width on overlying rock movement and fissure development in adjacent mine openings, a theoretical derivation and discrete element simulation approach was employed, utilizing the 8# coal seam in Baode Mine as a case study. The results demonstrate that, as a consequence of mining activities, the stress within the overlying rock layer of the mining area exhibits a distinctive pattern, comprising four distinct phases: concentration-unloading(yielding)-recovery-unloading-concentration. This pattern is observed to intensify with increasing coal column width. The elastic region in the center of the segmental coal column begins to appear as the width of the coal column increases. In addition, the vertical stress curve undergoes a transition from a single-peaked to a double-peaked configuration. Furthermore, the peak of the stress value demonstrates a decline in both velocity and magnitude. The peak stress value demonstrates a decelerating and decreasing trend. The coal column in the section transitions from a completely unstable state to a stable state in a gradual manner. The connectivity between the adjacent mining areas shifts from a completely through state to a gradually closed state. The sinking amount of the coal column in the section decreases from 2.56 m in the unstable state to 0.49 m in the 30 m width and exhibits a tendency towards stability. The findings of the theoretical derivation and simulation analysis suggest that the optimal width for coal columns in the section is approximately 20–25 m.