Prevention Of Dynamic Disasters Research Articles

True triaxial modeling test of high-sidewall underground caverns subjected to dynamic disturbances

Seismicity resulting from the near- or in-field fault activation significantly affects the stability of large-scale underground caverns that are operating under high-stress conditions. A comprehensive scientific assessment of the operational safety of such caverns requires an in-depth understanding of the response characteristics of the rock mass subjected to dynamic disturbances. To address this issue, we conducted true triaxial modeling tests and dynamic numerical simulations on large underground caverns to investigate the impact of static stress levels, dynamic load parameters, and input directions on the response characteristics of the surrounding rock mass. The findings reveal that: (1) When subjected to identical incident stress waves and static loads, the surrounding rock mass exhibits the greatest stress response during horizontal incidence. When the incident direction is fixed, the mechanical response is more pronounced at the cavern wall parallel to the direction of dynamic loading. (2) A high initial static stress level specifically enhances the impact of dynamic loading. (3) The response of the surrounding rock mass is directly linked to the amplitude of the incident stress wave. High amplitude results in tensile damage in regions experiencing tensile stress concentration under static loading and shear damage in regions experiencing compressive stress concentration. These results have significant implications for the evaluation and prevention of dynamic disasters in the surrounding rock of underground caverns experiencing dynamic disturbances.

Dynamic mechanical behaviours of frozen rock under sub-zero temperatures and dynamic loads

Dynamic mechanical behaviours of frozen rocks are essential for dealing with the design and stability of various engineering structures in cold regions. A dynamic-cryogenic testing system integrated with high-speed Digital Image Correlation (DIC) is adopted to investigate the dynamic mechanical behaviours of rock subjected to ambient room and sub-zero temperatures, along with high-rate loading. Dynamic compression, tensile and Mode I dynamic fracture tests were performed at 20, -20, −50 and −70 °C using dry and saturated sandstone from Yulong Copper Mine at high-altitude cold region. A DIC-based approach using pixel-based virtual extensometers is proposed to accurately capture the real-time cracking speed with high precision. The proportion of ice and unfrozen water in rock pores across various temperatures is quantified using the nuclear magnetic resonance (NMR) method. The results indicate significant temperature and rate dependencies in dynamic fracture toughness, crack propagation velocity, dynamic tensile strength, dynamic compressive strength, and failure modes; These parameters exhibit an increase with decreasing ambient temperature as unfrozen water transitions into ice, demonstrating the frozen effect of ice filling pores, supporting the rock skeleton, and bonding ice-rock interfaces. With decreasing temperature, crack branching becomes more pronounced in dynamic notched semi-circular bending (NSCB) tests. Additionally, dynamically compressed frozen rocks tend to transition from pulverization (Type II) to splitting (Type I) with multiple elongations, attributed to the strengthening effect. The findings elucidate the failure mechanisms observed in a higher proportion of larger blast blocks and hold valuable implications for blasting designs and dynamic disaster prevention in cold regions.

Analysis of mechanical response mechanism and energy evolution characteristics of saturated coal with a single pre-existing hole

It is essential to elucidate the mechanical mechanism of water injection and large-diameter drilling pressure relief measures on coal rock deformation and failure. This helps coal mines adopt more precise and effective dynamic disaster prevention and control measures. To obtain the mechanical response mechanism and energy evolution characteristics of saturated coal with a single pre-existing hole, uniaxial compression tests was carried out, and the deformation and failure process of coal samples were monitored by high-speed camera and acoustic emission monitoring systems. It is found that water saturation, single pre-existing hole measures, and their coupling effect resulted in a deterioration in the coal sample's strength by approximately 23.49%, 9.47%, and 47.95% respectively. The final failure mode of coal samples with different measures is shear failure. The law of fracture development and expansion and energy accumulation and release in different coal samples is roughly the same, the speed of energy accumulation and release in different stages is different. Water saturation and single pre-existing hole measures can affect the impact risk of coal samples, and water saturation can significantly reduce the impact tendency of coal samples, and reduce the impact energy index of complete coal samples by 56.59%. The impact tendency index of natural coal sample is slightly increased by single pre-existing hole measure, and the impact energy index of intact coal sample is reduced by 46.78% by the coupling of the two measures. These findings can provide technical support for coal mine power disaster prevention and control.

Dynamic mechanical response and crack evolution law of raw coal loaded by dynamic-static coupling under three-dimensional constraints

This paper presents the investigation of the dynamic mechanical properties of coal rock under complex stress conditions at depth, based on the improved Separate Hopkinson Pressure Bar Test System. A total of 15 groups of coal samples were used to perform dynamic impact tests under different conditions. The changing rules of dynamic strength, crushing, fractal dimension and damage modes of coal under different stress conditions were analyzed. A total of nine groups of coal samples were selected for numerical simulation using ANSYS/LS-DYNA. The results show that: (1) The stress–strain curves of coal specimens under different strain rates, different confining pressures and axial pressures have basically the same trend and the curves show a certain jump forward. (2) The peak dynamic stress of the coal specimens increased linearly with the increase of strain rate and confining pressure, and the ambient pressure limited the expansion of internal cracks of the coal specimens under impact loading. Based on the experimental and simulated data, the maximum relative errors between the experimental and simulated data were determined to be 2.9578% for Group A, 6.177% for Group B, and 6.382% for Group C, respectively. (3) The damage modes of the coal samples under the three-dimensional dynamic-static combined loading were mainly “X” type and “conical” shear damage. The fractal dimension increases with the increase of strain rate, decreases with the increase of confining pressure, and first decreases and then increases with the increase of axial pressure. This research achievement can provide theoretical support for the prevention of dynamic disasters in deep coal mine engineering.

Experimental Study on Dynamic Tensile Mechanical Behavior and Fracture Mechanical Characteristics of Sandstone with a Single Prefabricated Fissure

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock’s fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock’s dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone’s dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits “double peak” characteristics; when it exceeds 30°, a “single peak” waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone’s fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space.

Mining stress formation and distribution: Predictive model based on overburden key strata structure

AbstractIn coal mines, the effective extraction of relief gas and the prevention of dynamic disasters depend on accurate predictions of the spatial distribution of mining stress in the overlying rock. However, at present, the prediction of stress relief and concentration zones based on operational experience or empirical modeling differs significantly from actual measurements in the field. The fundamental problem is the difficulty in modeling the transfer mechanism of the mining overburden load under the influence of key strata. In this study, a mechanical model of the spatial distribution of the mining stress field based on the structure of overburden key strata was established. The model demonstrates that the key strata are the main bearing bodies of the overlying rock, both before and after the fracture, and the overburden rock load can be transferred to the coal and rock mass around the stope through the key strata in the fracture and bending subsidence zones, thus forming a mining stress field. Equations for calculating the plane distributions of mining stress under the key strata at different horizons and abutment pressures on the stope were established, and a spatial distribution prediction method for the mining stress field based on the overburden key strata structure was proposed. The study area was the Gaojiapu Coal Mine, where it was found that the key stratum of the 400.45 m thick Luohe Formation sandstone bore most of the overlying rock load and transferred the load to the coal and rock mass around the stope. This load distribution is the root cause of a high concentration and wide influence range of mining stresses, leading to serious deformation of the main roadway and frequent dynamic disasters. The mining stress concentration was maximized at a mining length of 1458 m × 1458 m.

Study on Dynamic Parameters and Energy Dissipation Characteristics of Coal Samples under Dynamic Load and Temperature

Coal and rock dynamic disasters such as rock burst and outburst seriously threaten the sustainable development of the coal mining industry, which are intimately correlated with the nonlinear dynamic response process of the deep coal and rock mass. This study conducts coal dynamic experiments under vibration load from room temperature to 60 °C by using the split Hopkinson bar (SHPB) with a temperature real-time control system and analyzes the variation in stress and strain and the energy dissipation characteristics of coal during the dynamic load process. The expression equation of dissipated energy of coal at different scales is established, and the judgment conditions of the macroscopic mechanical behavior of coal are analyzed theoretically. The stress curves show a multi-stress peak phenomenon when the coal samples are subjected to different temperatures and dynamic loads, and the coal’s dynamic stress and temperature show a polynomial fitting relationship at different stages. When the coal sample is subjected to temperature and dynamic load, the macroscopic changes in incident energy, reflected energy, and dissipated energy are consistent; that is, various energies gradually increase to a fixed value and tend to stabilize with the time of stress wave action. The transmission energy exhibits a rising trend in correlation with the duration of the dynamic load action, but the value is less than 0.1 J. The growth gradients of the different energies, in descending order, are: the growth gradient of incident energy, reflection energy, dissipation energy, and transmission energy. The energy inflection point appears at 60 °C. Based on the linear elastic fracture mechanics and damage mechanics theories, the expression for coal energy dissipation from the nanoscale to the microscale is established, and the relationship between energy dissipation and macroscopic mechanical behavior response of the coal samples is analyzed. The main physical components of the coal sample are calcite and kaolinite. Within the temperature range of 18–60 °C, the macroscopic failure form of the coal is horizontal tensile failure. The study results are introduced into dynamic disaster prevention and control and the surrounding rock system stability evaluation in deep mines.

Accurate prediction of indicators for engineering failures in complex mining environments

Due to seismic load, complex geological and geo-mechanical conditions of rock mass in Steeply Inclined and Extremely Thick Coal Seam (SIETCS) mines, the prediction and prevention of dynamic disasters remain quite challenging. Traditionally, physical models and numerical simulations are widely practiced for disaster prediction at shallow depths which becomes difficult in SIETCS mines. The drilling tests and above models are generally time-consuming and uneconomic providing miniature coverage. Whilst, rockburst driven disasters require detailed regional geological understanding and mechanical behavior of rock mass. For this purpose, a non-invasive and cost-effective geophysical workflow covering regional-scale geology is introduced for accurate identification and prediction of rockburst in a SIETCS mine of northwestern China. Passive seismological in-situ observations were made for a period of twenty-four months to compute the seismic source parameters, map fracturing process, identify regional lineaments and calculate important rockburst prediction indicators. The spatiotemporal distribution of induced-microseismicity, three-states stress theory, and mapped fractures helped in the identification of three rockbursts, several high-energy tremors, and the prediction of two new rockburst-prone regions. The mapped fractures through the novel ‘Seismo-Frac model’ showed that for the simultaneous excavation in B3 + 6 and B2 + 1 coal seams subjected to repetitive episodes of seismic deformation, the shear-displacement accumulation, prying effects of rock pillar and roof coupled with dynamic stress are the primary mode of deformation. The mapped fractures and lineaments are unevenly distributed in the minefield with a maximum density of the fractures concentrated in the B3 + 6 coal seam and rock pillar. Furthermore, through conditional probability analysis, the prediction efficiency of source parameter averages (E and N), seismological parameters (b-value and Δb), and maximum potential magnitude (Mm) was compared. A sharp-increase in source parameter averages while a sharp-decrease in the seismological parameters proved to be effective rockburst prediction indicators. This study also introduces decreasing occurrence frequency of fractures and lineaments as the new prediction indicators. This method, while a panacea for imaging the entire fracturing phenomenon, provides insights with widespread implications for academic researchers and industry practitioners to mitigate dynamic disasters in global underground engineering excavation.

Dynamic mechanical mechanism and optimization approach of roadway surrounding coal water infusion for dynamic disaster prevention

Roadway surrounding coal water infusion is a most significant technical means for the dynamic disasters prevention. To evaluate its efficiency in dynamic mechanical environment, the damage distribution and mechanical parameters were analyzed before and after water infusion. And the relationship among damage distribution, dynamic mechanical parameters, and stress wave propagation were established. With the medium of the wave impedance, the stress wave transmission process was characterized, and the dynamic stability criterion was established from the perspectives of energy and stress, respectively. On this basis, the optimization approaches were further proposed and validated in practice. The results demonstrate that water infusion can effectively enlarge the wave impedance difference among each adjacent circumferential coal segment and damage range in the surrounding coal. It will enhances the stress wave attenuation, thereby protecting the roadway from dynamic failure. To better play its role, the optimization approaches should focus on increasing the damage degree and range of the microscopic fracture zone in surrounding coal. These findings provide valuable insights into the design and implementation of surrounding coal water infusion for dynamic disasters prevention.

Dynamic characteristics and deterioration mechanism of coal under distinct initial gas pressure

Additional to dynamic and static superimposed loads, gas effects frequently affect coal seams throughout the coal mining process. It is crucial to comprehend coal samples’ mechanical properties and deterioration mechanisms under distinct initial gas pressure conditions. Consequently, the dynamic compression experiment of coal samples was conducted utilizing a self-developed observable combined dynamic and static loading test system of gas-bearing coal (GAS). The mechanical characteristics including failure mode in coal samples under distinct initial gas pressures were studied. Furthermore, the mechanism of gas deteriorated mechanical parameters and aggravated the propagation of cracks when combined with dynamic and static loads was revealed. The conclusions are drawn as follows: The GAS can go through four stages of deformation: elastic stage, elastoplastic stage, plastic stage, and failure stage. Furthermore, the dynamic strength and failure strain deteriorated with increasing gas pressure. Based on computed tomography (CT) technology, it is found that the splitting-spallation composite cracks of impacted samples become more noticeable with rising initial gas pressure, and finally, the two kinds of cracks create a complex reticular crack system. Meanwhile, the crack volume and fractal dimension increase with rising gas pressure, indicating that gas can aggravate the coal’s failure degree. Under combined dynamic and static loads, the deterioration model of mechanical parameters of GAS is obtained, that is, with rising initial gas pressure, the dynamic strength of coal samples reduces and the failure strain rises synchronously. The main reason for the aggravation of compound failure in impacted samples is that the stress intensity factor rises with the rise of gas pressure. These conclusions enrich the basic theories such as the inducing mechanism of dynamic disasters caused by coal-rock-gas compounds and can offer a theoretical foundation for the technology employed in monitoring, early warning, and prevention of dynamic disasters in compounds.

Coal and rock dynamic disaster prevention and control technology in the large mining face of a deep outburst mine

Coal and rock dynamic disaster prevention and control technology in the large mining face of a deep outburst mine

Influence of Gas Pressure on the Failure Mechanism of Coal-like Burst-Prone Briquette and the Subsequent Geological Dynamic Disasters

Rock bursts and coal and gas outbursts are geodynamic disasters in underground coal mines. Laboratory testing of raw coal samples is the dominant research method for disaster prediction. However, the reliability of the experimental data is low due to the inconsistency of the mechanical properties of raw coal materials. The utilization of structural coal resources and the development of new coal-like materials are of significance for geodynamic disaster prediction and prevention. This paper studies the failure characteristics and dynamic disaster propensities of coal-like burst-prone briquettes under different gas pressures. A self-made multi-function rock–gas coupling experimental device was developed and burst-prone briquettes were synthesized, which greatly improved the efficiency and precision of the experimental data. The results showed that the burst proneness of the briquette was thoroughly reduced at a critical gas pressure of 0.4 MPa. When the gas pressure was close to 0.8 MPa, both the bearing capacity and the stored burst energy reduced significantly and the dynamic failure duration extended considerably, indicating the typical plastic-flow failure characteristics of coal and gas outbursts. The acoustic emission monitoring results showed that with the increase in gas pressure, the post-peak ringing and the AE energy ratio of coal samples increased, suggesting that the macroscopic damage pattern changed from bursting-ejecting of large pieces to stripping–shedding of small fragments adhered to mylonitic coal. In addition, the transformation and coexistence of coal failure modes were discussed from the perspectives of coal geology and gas migration. This study provides a new method for the scientific research of compound dynamic disaster prevention in burst coal mines with high gas contents.

Experimental study of the dynamic mechanical responses and failure characteristics of coal under true triaxial confinements

Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines. Thus, a modified true triaxial Hopkinson bar was employed to explore the dynamic mechanical behaviors of coal at different confining pressures (0–20 MPa) and strain rates (40–220 s−1). The results show that the dynamic peak stress is positively correlated with lateral static pre-stress σy and σz, but negatively correlated with axial static pre-stress σx. At approximate strain rates, increasing the lateral static pre-stress facilitates increasing the dynamic peak stress, but the minimum lateral static pre-stress is the primary factor limiting a significant increase in dynamic peak stress of coal. Furthermore, the dynamic differential stress is linearly related to the logarithm of strain rate, and the peak strain varies linearly with strain rate. However, there is no significant correlation between confining pressure and peak strain. Moreover, X-ray CT images and photographic fracture observations of coal samples show the failure patterns under uniaxial and triaxial conditions are splitting failure and shear failure, respectively. The device provides a viable approach for fully comprehending the dynamic mechanical behaviors of rock-like material in complex stress conditions.

Evaluation of Rock Brittleness Index under Dynamic Load

Rock is a typical brittle material, and the evaluation of its brittleness index has important guiding significance for hard rock resource exploitation, unconventional oil and gas resource exploitation, mechanical driving efficiency, rock burst prediction, and dynamic disaster prevention and control. At present, brittleness index often measures the brittleness of rock under static load; thus, whether it is applicable to dynamic load is worth exploring. In this study, static and dynamic uniaxial compression tests and Brazilian splitting tests were carried out on five kinds of rocks, including fine granite, coarse granite, shale, marble, and sandstone, using the INSTRON−1346 test system and split−Hopkinson pressure bar (SHPB), respectively. The brittleness index values of different rocks under static and dynamic load were determined, and the changes in the brittleness of rocks under different loading methods and different strain rates were studied. The definition of brittleness and the applicability of existing brittleness indices were also discussed. It was found that the loading rate amplified the variation of the brittleness characteristics of rock. When static load changes to dynamic load, the brittleness of rocks increases, and the brittleness relationship between different rocks remains unchanged. The more brittle the rock is under static load, the greater the range of brittleness enhancement is under dynamic load. It was also found that the brittleness of sandstone had an obvious effect on the strain rate. The brittleness of rock increases with the increase in strain rate, and the greater the strain rate, the greater the brittleness enhancement degree. These research results can provide reference values for dynamic disaster prevention and safe construction of deep rock projects such as mines and tunnels.

The influence of the internal structure of loaded composite coal-rock on the variation characteristics of electromagnetic radiation (EMR) signal

In this study, authors analysed the distribution law of the loaded coal-rock internal current field, and then derived a theoretical model of the loaded composite coal-rock with fracture. Then, the influence of fracture state in coal-rock on the time-frequency characteristics of the EMR signal was studied, and the relationship between the EMR characteristics and the coal-rock states was summarized and verified by uniaxial experiments. The results showed that: the superposition of multiple micro-current sources in the loaded coal-rock leads to changes in the EMR, and the properties of the internal fracture of the coal-rock affect the distribution of the internal current field, which causes the external EMR intensity to exhibit a characteristic of “slow increase - slow increase - steady increase - slow increase - rapid decrease” with time. In addition, the proportion of internal charged fractures is highly correlated with the degree of damage, and there is a quadratic or linear fit between the internal charged fractures and the EMR intensity at each stress stage, with a fit above 93%. Meanwhile, the frequency-domain features contain more information than the time-domain's, and the more severe the damage to the coal-rock, the more complex the EMR spectrum measured from the outside will be. When the main frequency is around 5 kHz, the deformation of the coal-rock is mainly elastic, but when the main frequency is around 20 kHz, the damage is mainly plastic. On this basis, loaded coal-rock could be divided into six loading stages from I to VI according to EMR characteristics, and the EMR intensity, main frequency bandwidth, energy distribution characteristics and spectrum composition of each stage are different, which are related to the coal-rock's internal fracture state. Moreover, the experimental results are consistent with the theoretical and simulation results. These results can help improve the coupling theory between coal-rock internal structure and EMR, and have theoretical and reference value for the study of coal and rock dynamic disaster prevention methods based on multi-source information fusion.

Coal-Rock Dynamic Disaster Prevention Mechanism Based on the Dual Loads of Dynamic Barrier and Static Pressure Relief by Hydraulic Slotting.

According to the characteristics of coal-rock dynamic disasters and hydraulic slotting, the mechanism of dynamic load barrier and static load pressure relief in hydraulic slotting is proposed. The stress distribution in a coal mining face and the slotted area of a section coal pillar is analyzed by numerical simulation. The results show that the slot formed by hydraulic slotting can effectively alleviate the stress concentration and transfer the high-stress area to a deeper coal seam. When slotting and blocking the dynamic load propagation path in a coal seam, the wave intensity of the stress wave transmitted into the slot is greatly reduced, so the risk of a coal-rock dynamic disaster is reduced. A field application of hydraulic slotting prevention technology was carried out in the Hujiahe coal mine. An investigation of microseismic events and an evaluation of the rock noise system show that the average event energy within 100 m mining mileage decreased by 18%, the microseismic energy per unit footage decreased by 37%, the times of strong mine pressure behavior evaluated in the working face decreased by 17%, and the number of risks decreased by 89%. In conclusion, hydraulic slotting technology can effectively reduce the risk of coal-rock dynamic disasters in mining faces and provides a more effective technical means for coal-rock dynamic disaster prevention.

Acoustic Emission Characteristics and Damage Evolution Analysis of Sandstone under Three-Point Bending Test

In order to study the prevention of roadway roof bending, sinking, and breaking and the prevention of dynamic disasters such as the appearance of rock bursts, three-point bending experiments of sandstone under different spans were carried out. By using stress loading system and acoustic emission technology, the acoustic emission characteristic parameters of the sandstone fracture process were analyzed, the precursory information of rock bending fracture was explored, and the evolution law of sandstone damage based on acoustic emission characteristics was obtained. The results showed that according to the variation of acoustic emission ringing count, the load-time curve was divided into four typical stages: the first stage showed an overall increasing trend; the second stage showed an obvious increasing trend; the third stage showed obvious accelerated growth and the acoustic emission ringing count reached the maximum at the moment of rupture. In the fourth stage, the amplitude and frequency of the ringing count are large and high. With the increase in span, the cumulative ringing counts of AE decreased, and the rate of change gradually decreased. The fracture process of three-point bending sandstone can reflect the precursor information of rock fracture from time domain, frequency domain, and R value (ratio of cumulative acoustic emission ringing count to cumulative energy count). In time domain, the evolution characteristics of AE cumulative ringing count stage II can be used to predict the three-point bending fracture of sandstone. The peak frequency shows a linear increase after a spike and then an accelerated increase to a rupture, and the boundary point between the spike and the linear and nonlinear can be obtained. The decrease in R value can indicate that the main crack is growing in the specimen. According to the damage rate, the characteristics of the damage variables can be divided into five stages: stationary and low, gradually increasing, gradually decreasing, main crack coalescence, and complete fracture. With the increase in span, the fracture damage shows a decreasing trend. The residual damage fluctuates between 0.38 and 0.40 due to the difference in crack propagation trajectory. It has theoretical research value for revealing the internal mechanism of rock bending and fracture and has engineering guiding significance for mine pressure and rock strata control and dynamic disaster prevention.

Fracture Evolution of Overburden Strata and Determination of Gas Drainage Area Induced by Mining Disturbance

Overburden strata fracture evolution is critical to dynamic disaster prevention and gas-relief drainage, so it is important to accurately determine the evolution relationships with mining disturbance. In this paper, experiments and numerical simulation were adopted jointly to characterize the time-varying fracture area of overlying strata. The experimental results showed that the roof strata gradually broke and collapsed with coal mining, which indicated the fractures of overburden strata developed in an upward direction. The fracture development causes were explained by numerical simulation, which showed that stress increase exceeded the strength of coal and rock strata, and fractures were formed and expanded. Both experiments and numerical simulation results showed the two sides and the top of fracture areas provided channels and spaces for gas migration and reservoir, respectively. In addition, the breaking angle of overburden strata and the height of fracture areas were analyzed quantitatively. Through microseismic monitoring at the mining site, the fracture scales and ranges of overburden strata were verified by the energy and frequency of microseismic events, which were consistent with the support of maximum resistance. The position of drainage boreholes was considered based on the results of overburden strata fracture evolution. Our study is aimed at promoting coal mining in safety and improving gas drainage with a sustainable approach.

Research on composite dynamic disaster prevention and control system of mine earthquake and shock in thick and hard rock mines

Abstract With the rapid entry into deep mining of coal mines in China, the impact composite dynamic disaster of thick and hard layer mines and mine earthquakes has increasingly become a major disaster that threatens the safe and efficient mining of deep coal. Studying its occurrence mechanism, disaster prevention and control system has become a new major scientific issue in the field of coal mine safety. This paper proposes a framework for a composite dynamic disaster prevention and control system framework for thick and hard rock mines. First, the gravity forms, extents and deformation characteristics of different rock layers of the structural model are analysed, and the expressions of concentrated force and periodic breaking step distance of rock beams in thick and hard rock layers at the fixed support end are deduced. Then, according to the cause of the shock composite dynamic disaster, finally, the specific testing and calculation methods of mine earthquakes in thick hard rock mines are designed. The regional and local measures to manage compound dynamic disasters are put forward. Experiments show that the system is successfully applied to the mining practice of working face, and the results of water conservancy and stress monitoring support the rationality of the system. And through the implementation of impact prevention and control measures, the safety and disaster prevention and control of the working face was finally realised.

Influence of temperature on gas desorption characterization in the whole process from coals and its application analysis on outburst risk prediction

With the continuing advance of deep coal mining, temperature has become an important factor affecting coal methane recovery and gas dynamic disaster prevention. However, the influence of coal temperature on the whole process of gas desorption (including initial period) and released gas energy has been rarely studied. In this paper using a self-designed gas desorption device, the gas desorption characterization, e.g. desorption capacity, desorption theoretical model and released gas expansion energy law under varied temperatures were investigated. The results show that the increased coal temperature increases the gas desorption capacity, e.g. desorption amount and rate. However, for the same coal sample, the increased effect under the same gas pressure is weaker than that under the same gas adsorption amount. Compared with exponential function, the gas desorption law at different temperatures is more in line with the power function. The ratio of initial desorption amount of gas (∼10 s) increases with the increasing temperature, even up to 50%. The initial released gas expansion energy accordingly increases with the increase of temperature, showing a linear change between them. Moreover, the change degree of initial released gas expansion energy is greater under the same gas adsorption capacity compared with the same gas pressure. Meanwhile, with the increase of desorption time the linear correlation degree between the initial released gas expansion energy and gas desorption amount decreases. This represents that shortening measurement time will make the outburst risk results more credible when the gas desorption amount is used to determine the outburst risk of coal masses.