Burst Tendency Research Articles

Research Progress on the Mechanisms and Control Methods of Rockbursts under Water–Rock Interactions

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.

Study on signal characteristics of burst tendency coal under different loading rates

In order to study the mechanics, acoustic emission (AE) and electromagnetic emission (EME) response law of bursting liability coal at different loading rates, uniaxial compression tests were carried out on coal mass from Konggu Coal Mine. The corresponding relations among mechanical properties, AE and EME signals in the process of coal failure under loading were analyzed, and the energy evolution law of coal failure with bursting liability under loading rate was discussed. The results show that within a certain range of loading rate, the higher the loading rate, the higher the compressive strength and peak load of bursting liability coal, and the shorter the time for coal to reach the peak load. Under different loading rates, the mechanics, AE and EME signals of coal samples can be well corresponded. When the loading rate is low, the number of blocks destroyed of coal sample is large and the block size is relatively small, and the blocks are mainly scattered around the test platform. When the loading rate is high, the number of damaged blocks is relatively small and the block size is relatively large, and the blocks are far away from the test bench. When loading at a low rate, the internal cracks in coal can be fully developed and connected, and the energy release rate is relatively uniform in the process of loading and failure of coal sample. In the case of high loading rate, the energy release rate of coal sample in the loading process is much smaller than that in the moment of failure. Combining the above test results with the actual situation of the working face, it can be concluded that the total energy stored in the coal of fast mining increases and the threshold of impact decreases compared with that of slow mining. Therefore, under the disturbance of external dynamic load, rapid mining is more likely to induce rock burst.

Study on the size effect of rock burst tendency of red sandstone under uniaxial compression

The study of rock burst tendency of rock masses with different sizes plays a key role in the prevention of rock burst. Through theoretical analysis, it is proposed that uniaxial compressive strength and deformation modulus ratio are the key mechanical parameters affecting rock burst occurrence. In order to find out the size effect of uniaxial compressive strength and deformation modulus ratio, theoretical analysis and uniaxial compression experiment are carried out on rock samples with different heights, different cross-sectional areas and different volumes. The results show that the smaller the uniaxial compressive strength is, the larger the deformation modulus ratio is, and the more likely rock burst are to occur. On the contrary, rock burst is still not easy to generate. The uniaxial compressive strength of rock samples with different heights, different cross-sectional areas and different volumes increases with the increase of rock sample size. The deformation modulus ratio of rock samples with different heights and different volumes shows an upward trend on the whole, while that of rock samples with different cross-sectional areas shows a downward trend on the whole. The fracture forms of rock are analyzed using the energy conversion law in the process of deformation and failure for three kinds of rock with different shapes and sizes.

Study of hydraulic cutting as a method to prevent coal burst disasters

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

Burst Failure Characteristics and Energy Evolution Law of Coal with Prefabricated Cracks at Different Angles

In order to study the influence of fissures on the burst tendency of coal, the test and numerical simulation of the burst tendency of coal with different burst angles were carried out. The evolution law of the burst tendency index of coal under the influence of burst angle was analyzed, and the mechanism of energy storage and release of coal under the influence of fissure angle was revealed. The results show that compared with the specimens without prefabricated cracks, the uniaxial compressive strength of the specimens with 0° cracks is reduced by 48.4%, the dynamic failure time is increased by 279.4%, the burst energy index is reduced by 54%, and the burst energy velocity index is reduced by 87.9%. After that, with the increase of prefabricated crack angle, the uniaxial compressive strength of coal increases gradually, the dynamic failure time decreases gradually, the burst energy index increases gradually, and the burst energy velocity index increases gradually. That is to say, the larger the crack angle contained in the coal body, the stronger the burst tendency of the coal body, but it is still lower than that of the complete coal body. With the increase of prefabricated crack angle, the proportion of prepeak elastic energy of coal body increases, the less energy dissipation in the whole loading process of coal body, and the faster energy release rate during failure. The research results can provide some theoretical support for the prevention and control of rock burst disaster.

Characterization of the Time–Space Evolution of Acoustic Emissions from a Coal-like Material Composite Model and an Analysis of the Effect of the Dip Angle on the Bursting Tendency

Rock bursts pose a grievous risk to the health and lives of miners and to the industry. One factor that affects rock bursts is the dip angle of the coal seam. Because of the uniquely high gas content of the coal in a mine in Shanxi Province, China, coal specimens were obtained from this mine to produce coal–rock combination specimens and test the effects of various seam inclinations. Using a DYD-10 uniaxial compression system and a PCI-8 acoustic emission (AE) signal acquisition system, we investigated the spatial and temporal evolution characteristics of the burst tendency of specimens with different coal seam inclination angles (0°, 10°, 20°, 30°, 35°, 40°, and 45°). Uniaxial pressure was applied to the specimens, and we found that, as the inclination angle increased, the coal–rock combination specimens exhibited structural damage and destabilization, which was attributed to the generation of an interface slip phenomenon. In all tests, the coal exhibited greater damage than the rock. There was an energy convergence at the coal–rock interlayer interface, which was the main carrier for the accumulated energy. The impact energy dissipation index is defined according to the energy dissipation properties of the loading process of coal–rock composites. As the inclination angle increased, the impact energy dissipation index, energy storage limit, compressive strength, elastic modulus, and other indexes gradually decreased. This effect was strongest where the angles were 40° and 45°. The indexes used to assess the impact propensity decreased to a notable degree at these angles, revealing that the burst tendency of coal–rock is curtailed as the inclination angle increases. The results of this research are of great importance to the early evaluation of mine burst risks and the sustainable development of coal utilization.

Experimental Study on Mode I Fracture Characteristics of Granite after Low Temperature Cooling with Liquid Nitrogen

Liquid nitrogen fracturing has emerged as a promising technique in fluid fracturing, providing significant advantages for the utilization and development of geothermal energy. Similarly to hydraulic fracturing in reservoirs, liquid nitrogen fracturing entails a common challenge of fluid–rock interaction, encompassing the permeation and diffusion processes of fluids within rock pores and fractures. Geomechanical analysis plays a crucial role in evaluating the transfer and diffusion capabilities of fluids within rocks, enabling the prediction of fracturing outcomes and fracture network development. This technique is particularly advantageous for facilitating heat exchange with hot dry rocks and inducing fractures within rock formations. The primary objective of this study is to examine the effects of liquid nitrogen fracturing on hot dry rocks, focusing specifically on granite specimens. The experimental design comprises two sets of granite samples to explore the impact of liquid nitrogen cooling cycles on the mode I fracture characteristics, acoustic emission features, and rock burst tendency of granite. By examining the mechanical properties, acoustic emission features, and rock burst tendencies under different cycling conditions, the effectiveness of liquid nitrogen fracturing technology is revealed. The results indicate that: (1) The ultimate load-bearing capacity of the samples gradually decreases with an increase in the number of cycling times. (2) The analysis of acoustic emission signals reveals a progressive increase in the cumulative energy of the samples with cycling times, indicating that cycling stimulates the release of stored energy within the samples. (3) After undergoing various cycling treatments, the granite surface becomes rougher, exhibiting increased porosity and notable mineral particle detachment. These results suggest that the cyclic application of high-temperature heating and liquid nitrogen cooling promotes the formation of internal fractures in granite. This phenomenon is believed to be influenced by the inherent heterogeneity and expansion–contraction of internal particles. Furthermore, a detailed analysis of the morphological sections provides insights into the structural changes induced by liquid nitrogen fracturing in granite samples.

Numerical study of mechanical properties and microcrack evolution of double-layer composite rock specimens with fissures under uniaxial compression

Layered and heterogenous fissured rock masses are ubiquitous in nature. Fissures exert significant influence as release surfaces and nucleation sites for failure in layered rock masses. However, key mechanisms controlling microcrack initiation and extension in layered and heterogenous rock masses remain unclear. We complete a suite of numerical (granular mechanics) and complementary physical compression experiments on layered rocks containing fissures in different modalities where the overlying layer is both stronger and stiffer. We complete this to understand the impact of local specimen and system stiffness on ultimate strength and modes of failure (stability). We systematically examine the influence of fissure angles, lengths and positions on the mechanical response, including observations of microcrack evolution and tendency for instability (i.e. rock bursting), constrained by acoustic emission (AE). Peak strength and overall elastic moduli vary in a predictable and systematic manner. The strengths and stiffnesses of the double-layer composite specimens fall between those of the homogeneous weak and strong single layer specimens. The AE counts, micro crack growth and failure characteristics of the double-layer composite specimens are closely related to the fissure angles, lengths and positions. Whether the weak rock or the strong rock contains fissures, the rock burst tendency of the double-layer composite specimens decreases in varying degrees–defining the potential of pre-blasting/fracturing to soften the mass. Fissure angles and lengths do not have to be too large. Additionally, failure in the double-layer composite specimens results not only from crack propagation in the weak layer, but also failure of the entire specimen when the length of the fissure in the strong layer is sufficiently large. These observations provide a reference for stability evaluation and disaster mitigation of layered rock masses in engineering.

Experimental Investigation on the Influence of Temperature on Coal and Gas Outbursts

With the increasing mining depth, the dynamic disaster of coal and gas outbursts in coal mines has become increasingly prominent, and the bursting liability of coal and rock mass in deep coal seam mining is a necessary condition for the occurrence of rock burst and an important index to measure the failure of coal and rock mass. Thermal damage leads to rock instability and failure, which seriously influences the safe and efficient operation of coal mines. To investigate the effect of thermal damage on the bursting liability of deep coals, the burst tendency index of standard coal was measured after subjecting it to thermal damage at different temperatures. The effects of different thermal damage temperatures on the uniaxial compressive strength index, dynamic failure duration, stiffness ratio index, effective impact energy index, residual energy index change rate, and impact energy velocity of the coal and the influence of the post-peak failure mode of the coal were evaluated. The results revealed that the uniaxial compressive strength of the coal generally decreased with increasing thermal damage temperature. At temperatures above 200 °C, the strength significantly decreased. The comprehensive impact property index indicated that, with increasing thermal impact temperature, the burst tendency first increased up to the peak value at 200 °C and then gradually decreased. With the increase in the thermal damage temperature, the burst tendency decreased and disappeared in the temperature range of 250–300 °C, and the failure mode of the coal changed from brittle failure to brittle plastic failure, and finally ductile failure. The influence of thermal damage on coal bursting liability is studied, which provides a theoretical basis for preventing and controlling coal impact ground pressure hazards.

The Effect of Pore Pressure on the Mechanical Behavior of Coal with Burst Tendency at a Constant Effective Stress

The mechanical evolution of coal is evident when the pore pressure and the surrounding stress alone influence it. However, the evolution of the mechanical response of saturated coal under the coupling effect of pore pressure and confining pressure needs further investigation. This study identifies the mechanical behaviors of burst tendency dry and saturated coal under the stress condition where confining and pore pressure simultaneously increase but keep the constant difference by conducting a series of triaxial compressions on high burst tendency dry and saturated coal samples. The results show that the elastic modulus (E) and strength (σpeak) of dry coal increase from 3.4 to 4.8 GPa and 78.5 to 92.6 MPa, respectively, and the macro shear failure angle decreases from 64.2° to 56.5° when the confining pressure increases from 9 to 15 MPa. However, these parameters show the opposite evolution law when the pore pressure increases. Furthermore, the E and σpeak of saturated coal decrease from 3.84 to 2.75 GPa and 73.4 to 60.3 MPa, respectively, and the macro shear failure angle of saturated coal increases from 64.7° to 72.4° when the confining pressure and pore pressure increase simultaneously. The coefficient μ is proposed to reveal the evolution of strength at the effective confining pressure. Furthermore, the Mohr–Coulomb failure criterion, including μ, is ameliorated for application in coal under pore pressure conditions. In addition, a model was developed to reveal the effect of a pore-rich layer on the angle of macrocracks, which was confirmed by acoustic emission. The research reveals the mechanical behavior of coal under high pore pressure. Improved Mohr–Coulomb criterion criteria provide new guidance and vision for the analysis of coal instability in high pore pressure coal seams.

Effect of Loading Rates on Mechanical Characteristics and Rock Burst Tendency of Coal-Rock Combined Samples

According to the universal law of thermodynamics, the failure of any substance is closely related to its energy change. Understanding the strain energy and rock burst tendency of rock or coal under different loading rates is critical in many geological projects, such as mining, tunneling, and other underground engineering project. The mechanical and energy evolution characteristics of the coal-rock combined sample under different loading rates of uniaxial compression were numerically investigated. And, the rock burst tendency was also calculated by the Rock Burst Energy Index KE. The results show that with the increase of the loading rate, the total input energy, elastic strain energy, and dissipation energy all show an increasing trend. But the growth trend is different. And, under the five loading rates, the Rock Burst Energy Index KE of the coal-rock combined sample were all between 1.5 ≤ KE < 5. That is, they all have weak rock burst tendency. And the rock burst energy index increases first and then decreases with the increase of loading rates. This study provides references for propulsion speed of working face in the field mining practice.

Experimental and numerical study on fracture characteristics and constitutive model of sandstone under freeze-thaw-fatigue

The present paper proposes a whole-process constitutive model of rock mass under freeze-thaw-fatigue based on the Drucker-Prager criterion and the Lemaitre strain equivalence hypothesis and by using a Weibull distribution. The fracture characteristics of rock mass under freeze-thaw-fatigue are studied from a macro and mesoscopic perspective, by using the discrete element method and acoustic emission technology. The results show that as the number of freeze-thaw treatments increases, the b value fluctuation amplitude of the rock mass at fatigue failure decreases, the shear crack increases, the anisotropy of the mesoscopic force field enhances, and the required energy decreases, and the rock burst tendency weakens.

Investigation of Rock Burst Mechanism under Thermomechanical Coupling Conditions Based on Rock Mechanical Tests

Abstract The thermomechanical (TM) coupling effects of rock bursts have attracted considerable attention from researchers owing to the high geothermal and geostresses in deep tunnels in regions such as Western China. To study the brittleness and rock burst mechanism under TM conditions, various tests, such as splitting, uniaxial compression, rock burst tendency, and rock burst physical model tests, were conducted at temperatures ranging from 20°C to 80°C. The results revealed that, when granite samples were heated, their tensile strengths decreased in the splitting tests. Their peak stresses and the corresponding strains increased; their macroscopic tensile fracture surfaces became more evident; and the microcosmic tensile properties of intergranular fractures became prominent under uniaxial compression. Rock burst physical model tests and acoustic emission monitoring results revealed that, at higher temperatures, the fracture degree and failure range were larger, the energy was higher and more concentrated during failure, and failure occurred earlier. The brittleness index B, rock burst tendency Wet, and σθ/σc all exhibited a clear increasing tendency with an increase in temperature. The rock burst mechanism, considering the temperature effect, can be summarized as follows: the increase in brittle tensile fracture components and geostress caused by temperature increasing is conducive to the rapid release of energy, which will promote the occurrence of rock burst. The researching result is of great academic value and practical significance for the prevention, design, and safe construction of rock burst in deep high geothermal tunnels.

Applied Research of Water Jet Technology in Preventing Rock Burst Occurred in Roadways

Taking mining area 2502 in the Huayan mine field which was affected by strong geological tectonic stress as an engineering background, the water jet technology is studied through in-site survey, laboratory test, theoretical analysis, numerical simulation, and field industrial test. The research results are as follows: the burst tendency of No. 5 coal seam can be reduced to a certain extent after softening with water, and then the water jet technology is used to prevent rock burst of roadways; the typical characteristics of rock-burst accidents mainly cause heaving floor and serious deformation of two sides. The occurrence mechanism of rock burst in roadway ribs has two different forms, and they are static load dominant type and dynamic load dominant type. The abutment stress concentration value is higher than a certain concentration static load, it will affect the coal and rock medium in the floor, and the coal and rock medium in the floor will be transformed into a plastic state and then occur rock burst; the water jet technology for roadway ribs can effectively prevent rock burst of roadway ribs and floor based on the dynamic and static loads superposition theory and Terzaghi theory. Based on the results of numerical simulation, the specific parameters of water jet technology for roadway ribs in 250204 tailgate are as follows: the diameter and length of initial borehole are 110 mm and 20.0 m, the diameter and length of water jet section are 500 mm and 15.0 m, and the spacing between adjacent water jet boreholes is 3.0 m; the monitoring result of signal intensity by EMR indicates that the decreasing amplitude of signal intensity of EMR is about 60.2% on the side of coal-pillar rib, and the decreasing amplitude of signal intensity of EMR is about 68.6% on the side of solid-coal rib; the convergences monitoring result indicates that the convergence ratio of roadway height is about 3.2%, and the convergence ratio of roadway width is about 2.3% in the pressure relief roadway part; the water jet technology is not only helpful to the prevention of rock burst for the roadway ribs but also can play a good prevention of rock burst for roadway floor. The research results provide a theoretical foundation and a new guidance for preventing rock burst in roadway ribs and floor with similar engineering geological conditions.

Study on Pressure Relief Zone Formed Inside Roadway Rib by Rotary Cutting with Pressurized Water Jet for Preventing Rock Burst

Based on the engineering geological conditions of mining area 2502 in Yanbei coal mine as a background, the comprehensive index method is used to evaluate the rock burst risk of mining area 2502, and the burst tendency of coal seam 5# under natural and water‐saturated conditions is also tested in laboratory. Then the pressurized water jet technology is proposed as an effective and feasible method to prevent rock burst. By means of theoretical analysis, the coal‐rock mass system has three strain‐stress states under the influence of static load, and it has another strain‐stress state under the influence of static and dynamic combined load; meanwhile, the greater the horizontal tectonic stress caused by fold structure is, the more prone to instability and failure and induce rock burst coal mass composed of countless cell cubes is; when a pressure relief zone is formed inside the roadway rib by using pressurized water jet technology, the initial single peak stress curve will change to a final bimodal stress curve inside the roadway rib. A “strong‐weak‐strong” prevention structure can be formed inside the roadway rib and this prevention structure can well prevent the occurrence of rock burst. By means of numerical simulation analysis, the optimal diameter, length, and interval of rotary cutting sections are identified as 400 mm, 3.0 m, and 15.0 m, respectively. By means of on‐site industrial application analysis, all these monitoring results verify that when the pressurized water jet is used to conduct rotary cutting of roadway rib, a large‐scale pressure relief zone will be formed in the coal mass inside the roadway rib, and it can achieve the purpose of preventing rock burst in the roadway rib. The research results can effectively provide theoretical foundation and a new guidance for preventing rock burst with similar engineering geological conditions.

Experimental and Numerical Simulation of Coal Rock Impact Energy Index Based on Peridynamics

In response to the increasing severity of the rock burst phenomenon and its relatively difficult prediction, peridynamics and indoor uniaxial compression experiments were used to calculate the changes of the internal elastic energy (t) and impact energy (c) for different rock masses during a loading process from an energy perspective. Two traditional indices for judging rock burst tendency—the rock elastic deformation energy index (WET) and the rock impact energy index (WCF)—were combined to define a new actual impact energy index (W) to more accurately determine the occurrence tendency of rock bursts. The LAMMPS software was used to simulate the internal energy changes of rock materials under pressure, and the results were compared with experimental results for verification. The results were as follows: (1) in the uniaxial compression experiments of different specimens, fine sandstone had the strongest impact resistance, followed by coarse sandstone, mudstone, bottom coal seam, and top coal seam, and the obtained material properties provide a reference for predicting the rock bursts of various rock types in practical engineering. (2) The values calculated using the actual impact energy index (W) and the simulation value were 1.75 and 1.77, respectively, which corresponded to a lower error than when the rock impact energy index (WCF) and the rock elastic deformation energy index (WET) were used individually. Thus, this index can better predict the rock burst. (3) The simulated specimen was subjected to a gradual increase in the internal stored elastic energy during compression, which gradually decreased after the ultimate compressive strength was exceeded. The degree of impact damage formed after macroscopic crushing occurred depended on its residual energy.

Inverse analysis of dynamic failure characteristics of roadway surrounding rock under rock burst

AbstractRock burst is one of the most serious dynamic disasters in the process of coal resources mining, in order to study its occurrence mechanism and the characteristics of its impact on roadways. Based on the No. 25110 working face of Yuejin Mine in Yi Coal Mine and No. 21032 return air uphill event in Qianqiu Mine, combined with geological conditions, shock location, and source waveform, this paper uses numerical simulation to inverse the dynamic response characteristics of roadway surrounding rock under rock burst. The results show that the plastic strain energy density of No. 25110 working face in Yuejin Mine is mainly distributed around the roadway, and the maximum plastic strain energy density is 3.30 × 107 J at 75 ms, all rock masses around the roadway are damaged, and the maximum damage variable value is 0.44. The plastic strain energy density of No. 21032 return air uphill in Qianqiu mine is mainly distributed around the lower side of the roadway, and the maximum plastic strain energy density is 2.68 × 108 J at 80 ms, all rock masses around the roadway are damaged, and the maximum damage variable value is 1.76, indicating that the rock masses at the roof and two sides of the roadway have been damaged after the impact. Based on the results of numerical simulation, the energy gradient criterion of rock burst tendency was proposed, the degree of energy accumulation of surrounding rock is measured by the change amplitude of energy gradient, and the tendency index of rock burst is quantified, which provides a new method for the prediction of rock burst.

Investigation of mechanical and energy evolution characteristics for sandstone after high temperature damage under cyclic loading

During the production of underground engineering, investigating the mechanical behaviors of rock materials after high temperature damage is of great importance for controlling the stability of the underground structure. In this paper, for revealing the deformation and energy evolution laws of rock materials after high temperature damage under cyclic loading, a series of uniaxial compressive and cyclic loading experiments were conducted on sandstone after various high temperature damages, i.e., 200, 300, 400, 500, 600, 700, 800, and 900°C, to study the effect of high temperature on primary wave velocity, microstructure, deformation, strength, energy, etc. It can be observed that the primary wave velocity and microstructure weakened seriously with the development of high temperature damage and the uniaxial compressive strength of samples increases toward the maximum value with a high temperature damage of 300°C and then decreases gradually. The energy proportion index was established to characterize the influence of high temperature damage and cyclic stress levels on energy evolution laws of samples. With an increase in temperature, compared with input energy, elastic strain energy proportion decreases and dissipated energy proportion rises up, which indicate that the property of samples transforms from elasticity to plasticity. Finally, the variation laws between the burst tendency of the sample and high temperature damage were well described by presenting the average elastic energy index, which provides references for studying failure characteristics of rock materials.

Experimental Study of the Influence of Moisture Content on the Mechanical Properties and Energy Storage Characteristics of Coal

Rock burst occurs frequently as coal mining depth goes deeper, which seriously impacts the safety production of underground coal mines. Coal seam water injection is a technique commonly used to prevent and control such accidents. Moisture content is a critical factor tightly related to rock burst; however, an in-depth insight is required to discover their relationship. In this study, the influence of moisture content on the mechanical properties of coal and rock burst tendency is explored via multiple measurement techniques: uniaxial compression test, cyclic loading/unloading test, and acoustic emission (AE) test. These tests were performed on coal samples using the MTS-816 rock mechanics servo testing machine and AE system. The testing results showed that with the increase in moisture content, the peak strength and elastic modulus of each coal sample are reduced while the peak strain increases. The duration of the elastic deformation phase in the complete stress-strain curves of coal samples is shortened. As the moisture content increases, the area of hysteretic loop and elastic energy index W ET of each coal sample are reduced, and the impact energy index K E is negatively correlated with the moisture content, whereas dynamic failure time is positively correlated with the moisture content, but this variation trend is gradually mitigated with the continuous increase of moisture content. The failure of the coal sample is accompanied by the sharp increase in the AE ring-down count, whose peak value lags behind the peak stress, and the ring-down count is still generated after the coal sample reached the peak stress. With the increase in moisture content, the failure mode of the coal sample is gradually inclined to tensile failure. The above test results manifested that the strength of the coal sample is weakened to some extent after holding moisture, the accumulative elastic energy is reduced in case of coal failure, and thus, coal and rock burst tendency can be alleviated. The study results can provide a theoretical reference for studying the fracture instability of moisture-bearing coal and prevention of coal and rock burst by the water injection technique.

The Influence of Fracture Strain Energy on the Burst Tendency of Coal Seams and Field Application

Coal is typically considered a special engineering rock mass because of its low strength, high internal fracture development, good permeability, and random distribution of microparticles and fractures. The results of cyclic loading and unloading tests indicate that the strain energy during the coal deformation process can be divided into three parts: plastic strain energy; fracture strain energy; and base-material strain energy. The energy composition ratio differs depending on coal strength. Lower proportions of fracture strain energy are associated with higher elastic energy indexes, and there is a negative correlation between fracture strain energy and other coal burst tendency indexes. The results were applied on the 4206 isolated island working face of coal mine A in Yan’an, Shanxi, China, yielding good benefits. The findings presented here provide a theoretical basis for understanding the principle of coal seam bursting and guidance for reducing burst risks.