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16 pages, 16755 KiB

Open AccessArticle

Study on the Evolutionary Characteristics of Acoustic–Magnetic–Electric Signals in the Entire Process of Coal and Gas Outburst

by Jianchun Ou, Enyuan Wang, Zhonghui Li, Nan Li, He Liu and Xinyu Wang

Sustainability 2023, 15(22), 15944; https://doi.org/10.3390/su152215944 - 14 Nov 2023

Viewed by 546

Abstract

In recent years, with the continuous increase in the depth and intensity of coal mining, coal and gas outburst disasters pose a severe threat to the safe production of coal mines. Thus, this experiment studied the characteristics of electromagnetic radiation, acoustic emission, and [...] Read more.

In recent years, with the continuous increase in the depth and intensity of coal mining, coal and gas outburst disasters pose a severe threat to the safe production of coal mines. Thus, this experiment studied the characteristics of electromagnetic radiation, acoustic emission, and electric potential signals during gas adsorption, stress loading, and the entire outburst process. The results indicate that during the adsorption process, different parts of the coal body exhibit variations in electric potential signals, electromagnetic radiation, and acoustic emissions. During the loading process, the consistency between the acoustic–electric signals and the load change rate is good, and at the moment of outburst, the acoustic–electric signals significantly increase with the ejection of coal and gas. Outbursts generally occur during the decline in electromagnetic radiation and acoustic emission signals, with the internal electric potential signal strength first decreasing then rapidly increasing and the surface electric potential directly rising. The closer to the outburst opening, the greater the change in signal amplitude. Based on the above experimental results, the outburst can be monitored through the acoustic–magnetic–electric precursory signal changes during the adsorption and loading processes, which is of great significance to the safety production and rapid excavation of coal mines. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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19 pages, 12651 KiB

Open AccessArticle

Application of the Time Function Model for Dynamic Deformation Prediction in Mining Areas under Characteristic Constraints

by Zhihong Wang, Huayang Dai, Yueguan Yan, Jintong Ren, Jibo Liu, Yanjun Zhang and Guosheng Xu

Sustainability 2023, 15(20), 14719; https://doi.org/10.3390/su152014719 - 11 Oct 2023

Cited by 1 | Viewed by 781

Abstract

The fundamental model for dynamically predicting surface subsidence is the time influence function. However, current research and the application of time functions often neglect the comprehensive characteristics of the entire surface deformation process, leading to a less systematic representation of the actual deformation [...] Read more.

The fundamental model for dynamically predicting surface subsidence is the time influence function. However, current research and the application of time functions often neglect the comprehensive characteristics of the entire surface deformation process, leading to a less systematic representation of the actual deformation law. To rectify this, we explore ground point deformation along the strike line from two perspectives: dynamic subsidence and dynamic horizontal movement. Moreover, we develop prediction models for dynamic subsidence and dynamic horizontal movement at any point along the strike line, utilizing the probability integral method (PIM) and considering the surface deformation features. We then use characteristic constraints based on the prediction models to constrain the time influence function. For this purpose, we employ the Richards time function which has strong universality to establish the time functions for dynamic subsidence and horizontal movement under these constraints. We provide an illustrative example of its application in the 12,401 working face. Additionally, we explore the suitability of interferometric synthetic aperture radar (InSAR) technology for acquiring dynamic subsidence data on the surface. The experimental findings reveal the following key observations: the Richards model, when applied for dynamic subsidence prediction under constraints, exhibits high accuracy with an R-squared (R²) value of 0.997 and a root mean squared error (RMSE) of 94.6 mm, along with a relative mean square error of 1.9%. Meanwhile, the dynamic horizontal movement prediction model exhibits an accuracy in fully mined areas with an R² of 0.986, an RMSE of 46.2 mm, and a relative mean square error of 2.6%. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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13 pages, 3499 KiB

Open AccessArticle

Acoustic-Gas Coupling Response Law in the Whole Process of Coal and Gas Outburst

by Chaolin Zhang, Wei Zeng, Jiang Xu, Shoujian Peng, Shan Yin, Qiaozhen Jiang and Mingliang Liu

Sustainability 2023, 15(17), 12940; https://doi.org/10.3390/su151712940 - 28 Aug 2023

Viewed by 603

Abstract

The intensification of the global energy crisis has led to an increasing demand for coal. China is a major coal-producing country in the world and also the country with the most severe coal and gas outburst disasters. Thus, the coal and gas outburst [...] Read more.

The intensification of the global energy crisis has led to an increasing demand for coal. China is a major coal-producing country in the world and also the country with the most severe coal and gas outburst disasters. Thus, the coal and gas outburst experiment was conducted, and the following results were obtained: the whole outburst process was divided into three stages, namely the outburst preparation stage, the outburst gestation stage, and the outburst development stage. The gas pressure and acoustic emission signals show significant changes in all three stages, while the variation patterns are different. The gas pressure changes were strongest and the acoustic emission signals were highest during the development stage. Therefore, the outburst development stage was further subdivided into four phases, and the correlation between acoustic emission and gas pressure in each phase was analyzed in detail. Furthermore, the acoustic emission signals in three stages were compared and analyzed. The peak values of acoustic emission count and energy reached 285 times·s⁻¹ and 245 V in the preparation stage and reached 265 times·s⁻¹ and 231 V in the gestation stage, respectively, only 1.66%~1.78% and 2.19%~2.32% of the development stage, namely 15,980 times·s⁻¹ and 10,566 V. Moreover, it was found that the cumulative count and cumulative energy showed a parabolic relationship with the development time of the outburst. Based on the above experimental results, during the production process in coal mines, the dangerous state of outbursts can be monitored through gas pressure changes in the outburst preparation stage and gestation stage. Once in the development stage, more sensitive signals of acoustic emission and their fitting results are used for outburst hazard monitoring and early warning. Monitoring and warning of outbursts of combined gas pressure and acoustic emission signals can effectively improve the safety level of coal mine production. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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17 pages, 3043 KiB

Open AccessArticle

Numerical Investigation of the Evolution of Gas and Coal Spontaneously Burned Composite Disaster in the Goaf of Steeply Inclined Coal Seam

by Xiaojun Feng, Zichuang Ai, Xuebo Zhang, Qilei Wei, Chenjun Du, Qiming Zhang and Chuan Deng

Sustainability 2023, 15(12), 9246; https://doi.org/10.3390/su15129246 - 07 Jun 2023

Cited by 2 | Viewed by 854

Abstract

As the coal mine gets deeper and the stopes’ structures become more complex, gas and coal spontaneously burned composite disaster seriously threatens the efficient operation of coal mines. To study the interaction process and disaster-causing mechanism of gas and coal spontaneous combustion (GCSC), [...] Read more.

As the coal mine gets deeper and the stopes’ structures become more complex, gas and coal spontaneously burned composite disaster seriously threatens the efficient operation of coal mines. To study the interaction process and disaster-causing mechanism of gas and coal spontaneous combustion (GCSC), this paper establishes a numerical model to study the influence of drilling location/pressure and N₂ injection on the evolution of gas and coal spontaneously burned composite disaster in the goaf. The simulation shows that in the central part of the goaf, a combined area of gas and coal combustion poses a possibility of spontaneous combustion calamity, and the length of the compound disaster area is about 20 m. The methane (CH₄) explosion zone and the dioxygen(O₂) temperature rise zone do not overlap in the air entrance roadway and return air roadway, indicating that there is no risk of compound disasters. The optimal nitrogen (N₂) injection rate for this working face is 2000 m³/h, and the N₂ port should be located 25 m profound into the goaf, which can effectively drive the diffusion of N₂ and narrow the O₂ zone’s breadth. The findings have considerable engineering applications for revealing the evolution process, risk assessment and control for GCSC compound disasters in coal mines. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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15 pages, 3168 KiB

Open AccessArticle

A Study on Disasters Induced by Head-On Ejection in High-Speed Driving under the Influence of Roof Drainage

by Fenghui Li, Yunhai Cheng, Xiufeng Zhang, Dong Li and Shunjie Huang

Sustainability 2023, 15(11), 8580; https://doi.org/10.3390/su15118580 - 25 May 2023

Viewed by 694

Abstract

During the gob-side entry driving of the Jurassic coal seam in Western China, ejection disasters occur under the influence of roof drainage, which rarely appear in the eastern mining area. To address this problem, a method combining theoretical analysis, numerical simulation, and field [...] Read more.

During the gob-side entry driving of the Jurassic coal seam in Western China, ejection disasters occur under the influence of roof drainage, which rarely appear in the eastern mining area. To address this problem, a method combining theoretical analysis, numerical simulation, and field monitoring was used to study the disaster induced by head-on ejection during speedy driving under the influence of roof drainage in the context of gob-side entry driving of the 2202 auxiliary haulage roadway in a mine. A calculation model for the critical energy conditions for disasters induced by head-on ejection was established. The relationships between the driving velocity and the dynamic and static loads on the driving face and the disasters induced by ejection were clarified under the influence of roof drainage. The results indicate that the energy threshold for ejection-induced disaster is 12.23 kJ, and the elastic energy of the driving face induced only by static load fails to reach the energy threshold. When the driving velocity exceeds 5 m/d, microseismic activity in front of the driving face increases in a stepwise manner, and the influence of dynamic load intensifies. The superposition of accumulated elastic energy induced by static load and the energy transmitted by microearthquake to the driving face exceeds the energy threshold, resulting in the risk of ejection-induced disaster. Based on this, measures such as microseismic monitoring in front of the driving face, advanced pulverized coal monitoring, driving speed adjustment, and advanced pressure relief of large-diameter boreholes are adopted to ensure safe driving. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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19 pages, 2448 KiB

Open AccessArticle

A Comparative Investigation of the Adsorption Characteristics of CO₂, O₂ and N₂ in Different Ranks of Coal

by Haijian Li, Qiang Zeng, Jianhong Kang, Gang Cheng, Jianwei Cheng and Shengcheng Wang

Sustainability 2023, 15(10), 8075; https://doi.org/10.3390/su15108075 - 16 May 2023

Viewed by 986

Abstract

The adsorption mechanism of carbon dioxide, oxygen and nitrogen in coal is important for preventing and controlling coal spontaneous combustion and for understanding the technology of CO₂ storage in goaf. Adsorption amount and adsorption heat are key adsorption parameters that are required [...] Read more.

The adsorption mechanism of carbon dioxide, oxygen and nitrogen in coal is important for preventing and controlling coal spontaneous combustion and for understanding the technology of CO₂ storage in goaf. Adsorption amount and adsorption heat are key adsorption parameters that are required to understand the material and energy conversions during adsorption in coal. In this study, we studied the factors that influence the adsorption amounts and adsorption heat values of carbon dioxide, oxygen and nitrogen in coal by testing four different coal samples using conventional coal quality analysis, low-pressure nitrogen and carbon dioxide adsorption, Fourier transform infrared spectroscopy and three gas adsorption experiments at different temperatures. Then, we analyzed the relationships between the structural parameters of the coal samples and the adsorption amounts and the adsorption heat values of carbon dioxide, oxygen and nitrogen. The results show that the adsorption isotherms of carbon dioxide conform to the Langmuir equation, and the adsorption isotherms of oxygen and nitrogen conform to Henry’s law between 0 and 110 kPa. The adsorption amounts of carbon dioxide, oxygen and nitrogen decreased with an increase in temperature, and the change in the rate of the adsorption amount with temperature was determined by the adsorption heat. The results of the pore structure show that the pores of the coal samples are composed of mesopores and micropores; the micropores contribute to the main specific surface area. The micropore and mesopore structures are the main determinants of the adsorption amounts of carbon dioxide, oxygen and nitrogen in coal. The gas adsorption heat is affected by the pore structure and the chemical composition of coal. The adsorption heat of nitrogen correlates positively with the pore structure of the coal. The adsorption heat of oxygen correlates positively with the ash, elemental nitrogen, elemental sulfur and mineral contents of the coal. The adsorption heat of carbon dioxide correlates positively with the elemental sulfur content of the coal. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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17 pages, 3985 KiB

Open AccessArticle

Study on Height Development Characteristics of Water-Conducting Fracture Zone in Fully Mechanized Mining of Shallow Thick Coal Seam under Water

by Xikun Chang, Mingguo Wang, Wei Zhu, Jinmeng Fan and Mingyang Liu

Sustainability 2023, 15(9), 7370; https://doi.org/10.3390/su15097370 - 28 Apr 2023

Cited by 3 | Viewed by 747

Abstract

The height of water-conducting fracture zone (HWCFZ) is one of the important technical parameters for water-preserved coal mining. The purpose of this paper is to acquire information about the height development characteristics of water-conducting fracture zone (WCFZ) in fully mechanized mining of shallow [...] Read more.

The height of water-conducting fracture zone (HWCFZ) is one of the important technical parameters for water-preserved coal mining. The purpose of this paper is to acquire information about the height development characteristics of water-conducting fracture zone (WCFZ) in fully mechanized mining of shallow thick coal seam under water body in western mining area of China. The 91,105 fully mechanized mining face of Daheng coal mine under composite water body was taken as the research object, the development height, morphological characteristics, development and evolution process of WCFZ in working face mining were studied through underground up-hole water injection method by intervals, borehole TV and numerical simulation. The results show that the HWCFZ in 91,105 fully mechanized mining face is 52.7~53.6 m, and the fracture mining ratio is 12.55~12.76. The final development form is saddle-shaped with “large at both ends and small in the middle”. It is accurate and reliable to determine the development characteristics of overburden fractures and the HWCFZ by the field measurement of the combination of underground upward hole segmented water injection method and borehole TV. The development height of the water-conducting fracture zone obtained by numerical simulation is consistent with the field measured results. The development and evolution of the height of WCFZ presents four stages: “development–slow increase–sudden increase–stability”. When the WCFZ develops to a certain layer, the cracks generated by the weak strata in the fracture zone of overlying strata on the working face will automatically close with the advancement of the working face, resulting in “bridging phenomenon”, which inhibits the further development of the WCFZ. That is, the existence of soft rock with a certain thickness in overburden will become the key inhibiting layer for the development of WCFZ, effectively blocking the communication between water-conducting fracture and overlying aquifer. The research results are intended to provide guidance for the implementation of water preserving mining and ecological environment protection in ecologically fragile areas in western China. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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16 pages, 14498 KiB

Open AccessArticle

Seismic Reduction Mechanism and Engineering Application of Paste Backfilling Mining in Deep Rock Burst Mines

by Jiazhuo Li, Songyue Li, Wentao Ren, Hui Liu, Shun Liu and Kangxing Yan

Sustainability 2023, 15(5), 4336; https://doi.org/10.3390/su15054336 - 28 Feb 2023

Cited by 2 | Viewed by 1031

Abstract

In the process of coal resources development, a large number of strip coal pillars have been left behind in the coal mines in central–eastern China. With the increase in coal mining depth year by year, the rock burst threat of strip coal pillars [...] Read more.

In the process of coal resources development, a large number of strip coal pillars have been left behind in the coal mines in central–eastern China. With the increase in coal mining depth year by year, the rock burst threat of strip coal pillars is becoming more and more prominent due to the influence of buried depth, geological structure, gob and other factors. Backfilling mining is the main means to recover the residual strip coal pillar. In order to investigate the effect of backfilling mining on the prevention and control of rock burst, taking the paste backfilling workface 1# of Gucheng coal mine as the engineering background, a comprehensive research method of theoretical analysis, numerical simulation and field monitoring was used to study the evolution of stress and of the overburden spatial structure of the backfilling workface under the control of the backfilled ratio. The results showed that the backfilling mining controls the movement and deformation of overburden by reducing the activity range of roof strata. The overburden fracture development height decreases with the increase in backfilled ratio, but there is a boundary effect influenced by the roof deflection before backfilling and the defective distance of roof contact. With the increase in backfilled ratio, the concentration coefficient of front abutment pressure, the vertical displacement of the roof and the development height of the plastic zone of overlying strata decreased obviously, which indicates that filling mining can effectively control the stress of surrounding rock and the movement of overlying strata. The field monitoring data showed that the influence range of the front abutment pressure of the paste backfilling workface was about 90 m and the maximum stress of the surrounding rock of the two entries did not exceed 7 MPa. The average daily frequency of microseism was 1.34, and the average daily total energy of microseism was 1.80 + 10³ J, which decreased by 69% and 90%, respectively, compared with the caving method working face with similar geological conditions. The data above showed that the backfilling mining can effectively reduce the working face stress level and dynamic load strength to achieve the effect of prevention and control of rock burst. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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19 pages, 6260 KiB

Open AccessArticle

Analytical Prediction of Coal Spontaneous Combustion Tendency: Pore Structure and Air Permeability

by Bin Du, Yuntao Liang, Fuchao Tian and Baolong Guo

Sustainability 2023, 15(5), 4332; https://doi.org/10.3390/su15054332 - 28 Feb 2023

Cited by 5 | Viewed by 1303

Abstract

In previous research, many scientists and researchers have carried out related studies about the spontaneous combustion of coal at both the micro and the macro scales. However, the macroscale study of coal clusters and piles cannot reveal the nature of oxidation and combustion, [...] Read more.

In previous research, many scientists and researchers have carried out related studies about the spontaneous combustion of coal at both the micro and the macro scales. However, the macroscale study of coal clusters and piles cannot reveal the nature of oxidation and combustion, and the mesoscale study of coal molecule and functional groups cannot be directly applied to engineering practice. According to our literature survey, coal is a porous medium and its spontaneous combustion is a multi-scale process. Thus, the mesoscale study of coal’s spontaneous combustion is essential. In this manuscript, the mesoscale of the coal body (such as pore size, pore volume, and specific surface area), and the meso-scale structural morphological characteristics of the coal surface are finely analyzed and characterized. On this basis, the meso-scale structure of pores and fractures are digitally reconstructed. Furthermore, velocity and pressure distributions of the flow field in the pores of the scan plane are outlined and described by numerical simulation. The results indicate that, because of the pore structure characteristics and fluid viscosity, not all fluids in the pores demonstrate flow. This conclusion well explains the source of CO gas in methane extraction pipes, which is one of the main index/indicator gases of the spontaneous combustion of coal. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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16 pages, 4138 KiB

Open AccessArticle

The Failure Characteristics and Energy Evolution Pattern of Compound Coal–Rock under the Action of Cyclic Loading

by Guohua Zhang, Lei Wang, Tao Qin, Ji Li, Gang Liu and Yubo Li

Sustainability 2023, 15(5), 4133; https://doi.org/10.3390/su15054133 - 24 Feb 2023

Viewed by 970

Abstract

Based on the entire loading process of compound coal–rock, test pieces with three different coal/rock ratios (1:3, 1:1, and 3:1) have been constructed and the corresponding cyclic loading experiments have been carried out. Through the experiment, the deformation and failure characteristics of the [...] Read more.

Based on the entire loading process of compound coal–rock, test pieces with three different coal/rock ratios (1:3, 1:1, and 3:1) have been constructed and the corresponding cyclic loading experiments have been carried out. Through the experiment, the deformation and failure characteristics of the compound coal–rock samples have been explored and the stage evolution characteristics of energy density have been subsequently analyzed. Ultimately, the relation between deformation failure and the energy evolution mechanism has been established, and thus the reasons behind rock bursts in the coal–rock compounds have been discussed. The experimental results indicate that with the increase in cyclic loading, the stress–strain curve of the compound coal–rock demonstrates a positive shift, whereas the change in the hysteretic curve from dense to sparse results in a “hysteresis expansion”. The increase in the coal body height increases the chance of brittleness failure of the compound coal–rock. The coal body, as the main controlling factor of compound coal–rock failure, generates cracks that expand to the rock body along the juncture of the coal and rock, leading to instability. The energy density evolution curve can be described by a quadratic function. The evolution process is initiated from the slow increase in input energy density and elastic energy density. A large amount of energy is stored through the rapid increase in the density mentioned above. At last, the evolution is completed by a surge in dissipated energy. The energy evolution drives the crack expansions in the compound coal–rock under load. The energy accumulation in the compound coal–rock is increased by the exploitation of the clamping effect of the thick and hard top and bottom plate. The risk of rock burst is intensified by the failure of the coal body because of the energy in the coal–rock system. The study results help to comprehend the energy evolution pattern in the surrounding rock of deep mining roadways and expand the prevention methods for impact ground pressure. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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19 pages, 5988 KiB

Open AccessArticle

Experimental Study on Mechanical Properties and Failure Mechanism of Damaged Sandstone

by Yongqiang Zhao, Quansheng Li, Kai Zhang, Yingming Yang, Dongxiao Zhang, Weilong Zhang and Xiaojun Ding

Sustainability 2023, 15(1), 555; https://doi.org/10.3390/su15010555 - 28 Dec 2022

Viewed by 1164

Abstract

Solid materials such as rocks can contain primary defects, and internal defects are activated in the event of mining disturbance, which causes rock damage and destruction. Therefore, it is of great significance for rock engineering to study the mechanical properties and failure mechanism [...] Read more.

Solid materials such as rocks can contain primary defects, and internal defects are activated in the event of mining disturbance, which causes rock damage and destruction. Therefore, it is of great significance for rock engineering to study the mechanical properties and failure mechanism of damaged rock. In this study, damaged prefabricated crack sandstone specimens were prepared with the cyclic loading-unloading test, and the uniaxial loading test was carried out with damaged specimens. The evolution law of peak strength, elastic modulus, and peak strain of specimens with different damage degrees was studied, the quantitative relationship between the P-wave velocity and the damage degree was obtained, and the acoustic emission (AE) count and energy evolution characteristics of specimens with different damage degrees were analyzed. The energy evolution law of damaged specimens was revealed, and with the increase in damage degree, the elastic energy stored in the specimens can be converted into crack propagation more quickly, and the dissipated energy density increases rapidly, resulting in complete rock failure. The research results can provide theoretical support for the stability analysis and control of underground engineering rock mass in the event of multiple disturbances. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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12 pages, 7675 KiB

Open AccessArticle

Numerical Simulation Study on Deformation Characteristics of Surrounding Rock during Construction and Operation of Large Underground Gas Storage Structures

by Zhenhua Peng, Hao Ding, Xinghong Jiang, Xuebing Hu and Liang Cheng

Sustainability 2022, 14(24), 16864; https://doi.org/10.3390/su142416864 - 15 Dec 2022

Viewed by 1076

Abstract

Underground gas storage is an important technical measure for future natural gas storage. The stability of the surrounding rock during excavation and under ultra-high gas storage pressure is the key to the stable operation of gas storage reservoirs. A numerical calculation model for [...] Read more.

Underground gas storage is an important technical measure for future natural gas storage. The stability of the surrounding rock during excavation and under ultra-high gas storage pressure is the key to the stable operation of gas storage reservoirs. A numerical calculation model for different surrounding rock conditions, different depth-span ratios, and different buried depth conditions was conducted to study the stability of surrounding rock after large section underground gas storage excavation and under an ultra-high gas storage pressure of 20 MPa. The results show that after construction is completed, the deformation of the rock surrounding the cavern increases with a decrease in the surrounding rock grade, and the deformation of the rock surrounding the cavern increases as the burial depth increases. In addition, the maximum vertical deformation of the surrounding rock decreases with the increase in the depth-span ratio of the cavern, and the maximum horizontal displacement increases with the increase in the depth-to-span ratio. While operating at 20 MPa gas storage pressure, the displacement of the rock surrounding the chamber tends to increase with the decrease in the surrounding rock grade and the deformation of the surrounding rock of the chamber decreases as the burial depth increases. Furthermore, the vertical displacement of the rock surrounding the chamber decreases with the increase in the depth-span ratio, while the horizontal displacement of the surrounding rock increases with the increase in the depth-span ratio. Considering the stability of the surrounding rock during construction and operation, gas storage chambers should be built in areas with better conditions, such as Grade II and Grade III surrounding rocks within a burial depth range of 200 m. Moreover, the stability of the surrounding rocks is better when the chamber depth-span ratio is 2.5~3.0. These research results can provide a theoretical reference for the design of large underground gas storage structures. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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19 pages, 4578 KiB

Open AccessArticle

A New Method to Assess Thick, Hard Roof-Induced Rock Burst Risk Based on Mining Speed Effect on Key Energy Strata

by Wenlong Li, Shihao Tu, Hongsheng Tu, Xun Liu, Kaijun Miao, Hongbin Zhao, Jieyang Ma, Long Tang and Yan Li

Sustainability 2022, 14(22), 15054; https://doi.org/10.3390/su142215054 - 14 Nov 2022

Cited by 5 | Viewed by 1062

Abstract

Roof-type rock burst (RTRB) frequently occurs in the hard, thick roof of working faces, which causes roadway failure, facility damage and even personnel casualties. Previous research results show that mining speed has obvious effects on the rock burst risk and many rock burst [...] Read more.

Roof-type rock burst (RTRB) frequently occurs in the hard, thick roof of working faces, which causes roadway failure, facility damage and even personnel casualties. Previous research results show that mining speed has obvious effects on the rock burst risk and many rock burst accidents are caused by an unreasonable mining speed. To provide a theoretical foundation for the determination of a reasonable mining speed in a specific working face subjected to RTRB, in this study, the key energy strata (KES) principle contraposing the RTRB was proposed, and the criterion of KES was determined by defining the energy release coefficient k_c. On this basis, the energy accumulation characteristics of coal and energy release of surrounding rock were analyzed using FLAC3D numerical simulation. Accordingly, to assess the rock burst risk considering the mining speed effect, a new method was proposed and a new energy index Φ_vi was defined to divide rock burst risk with different mining speeds into four grades. To validate the availability of the KES principle and the new assessment method, they were adopted in a thick, hard roof working face. The application results indicate that the mining speed of 3.6 m/d obtained by the method meets the demands of safe and high-efficiency production. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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10 pages, 2096 KiB

Open AccessArticle

Research on Prediction of Coal Sample Deformation Based on Acoustic-Emission Sensitive Index

by Man Wang, Jianguo Zhang, Bing Jia, Weihang Du, Zhaofan Chen and Shuaitao Liu

Sustainability 2022, 14(22), 14875; https://doi.org/10.3390/su142214875 - 10 Nov 2022

Cited by 1 | Viewed by 957

Abstract

Establishing the relationship between the deformation of coal samples and acoustic emission response is the basis for the deformation prediction of coal samples. Using a combination of laboratory tests and theoretical analysis, acoustic emission tests of the uniaxial loading process were conducted on [...] Read more.

Establishing the relationship between the deformation of coal samples and acoustic emission response is the basis for the deformation prediction of coal samples. Using a combination of laboratory tests and theoretical analysis, acoustic emission tests of the uniaxial loading process were conducted on coal samples in the study area and the test results were analyzed, focusing on the rule of variation of acoustic emission counts with loading time. Based on the analysis of stress, strain, time, and acoustic-emission parameters variation, the relationship between the deformation of coal samples and acoustic emission response was established and analyzed. The analysis results show that during the loading process, the acoustic emission counts show the characteristics of stage changes, which can be divided into three stages: the initial stage with sporadic acoustic emission events, the middle stage with a stable increase of acoustic emission events, and the final stage with the rapid increase of acoustic emission events. This stage division has good consistency with the deformation stages of coal samples. Moreover, the acoustic emission counts have obvious and easily identifiable characteristics of changes in the deformation process of coal samples. The acoustic emission count can be used as a sensitive indicator in this study area to predict the deformation of coal samples. It provides a reference for the application of acoustic-emission prediction technology in this study area, which is important to improve the accuracy of geohazard prediction. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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20 pages, 9413 KiB

Open AccessTechnical Note

Precursory Analysis of Water-Bearing Rock Fracture Based on The Proportion of Dissipated Energy

by Lixiao Hou, Kewang Cao, Naseer Muhammad Khan, Danial Jahed Armaghani, Saad S. Alarifi, Sajjad Hussain and Muhammad Ali

Sustainability 2023, 15(3), 1769; https://doi.org/10.3390/su15031769 - 17 Jan 2023

Cited by 4 | Viewed by 1391

Abstract

In order to better understand the failure process of water-bearing rocks, samples of water-bearing sandstone were tested uniaxially. The failure process and the development of internal cracks were studied through the evolution characteristics of dissipated strain energy and particle flow simulation. In this [...] Read more.

In order to better understand the failure process of water-bearing rocks, samples of water-bearing sandstone were tested uniaxially. The failure process and the development of internal cracks were studied through the evolution characteristics of dissipated strain energy and particle flow simulation. In this study, we found that: (1) The presence of water in sandstone results in a reduction in energy storage capacity as well as strength. (2) The dissipated energy ratio curve of sandstone samples and simulated samples’ internal fracture development curve has obvious stages. The dissipated energy ratio turning point and the rapid fracture development point are defined as the failure precursor points of sandstone samples and simulated samples, respectively. In both sandstone samples and simulated samples, the ratio between failure precursor stress and peak strength remains almost unchanged under various water conditions. (3) The ratio of fracture to dissipated energy (RFDE) of sandstone is proposed, and interpreted as the increased number of cracks in the rock under the unit dissipated. On this basis, the fracture initiation dissipated energy (FIDE) of sandstone under different water cut conditions is determined, that is, the dissipation threshold corresponding to the start of the development of sandstone internal cracks. (4) The analysis shows that RFDE increases exponentially and FIDE decreases negatively with the scale-up in moisture content. Further, high moisture content sandstone consumes the same dissipative strain energy, which will lead to more fractures in its interior. The research in this paper can lay a theoretical and experimental foundation for monitoring and early warning of rock engineering disasters such as coal mining, tunnel excavation, slope sliding, and instability. Full article

(This article belongs to the Special Issue Coal and Rock Dynamic Disaster Monitor and Prevention)

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