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30 pages, 15886 KiB

Open AccessArticle

Study on Key Parameter Design and Adaptability Technology of the 110 Mining Method for the Yuwang NO.1 Coal Mine in the Diandong Mining Area

by Xingen Ma, Manchao He, Bing Hu, Dalong Wang, Cunqiang Chen, Jing Li, Jianxun Gao, Qi Jiang and Zongrong Bai

Minerals 2023, 13(2), 176; https://doi.org/10.3390/min13020176 - 26 Jan 2023

Cited by 5 | Viewed by 1573

Abstract

The 110 mining method is a high-efficiency entry-retaining technology without coal pillars or filling materials. At present, there is no precedent for its application in the Huaneng Group. In order to introduce this technology, it is planned to carry out experimental application research [...] Read more.

The 110 mining method is a high-efficiency entry-retaining technology without coal pillars or filling materials. At present, there is no precedent for its application in the Huaneng Group. In order to introduce this technology, it is planned to carry out experimental application research in the Yuwang NO.1 Coal Mine of the Huaneng Diandong mining area. The Yuwang NO.1 Coal Mine is a typical coal and gas outburst mine with a coal seam group. In view of the introduction of the 110 mining method under these conditions, first, the geological conditions of the Yuwang NO.1 Coal Mine in the Huaneng Diandong mining area are analyzed, the geological characteristics of the test mining face are summarized, and the practical feasibility of the 110 mining method is analyzed according to the geological characteristics of “one soft, one low, two high, and two complex”. Then, according to the engineering experience, calculations, and analysis, the key parameters of roof cutting of the test mining face in the Yuwang NO.1 Coal Mine are obtained, and with the help of a numerical simulation, the roof-cutting height, the roof-cutting angle, and the blasting parameters are numerically simulated and analyzed. The roof-cutting key parameters of the test face are obtained as follows: the roof-cutting depth is 7 m, the roof-cutting angle is 15°, and the blasting method is continuous hole blasting with 500 mm spacing. After that, according to the coal and gas outburst and the occurrence conditions of coal seams in the Yuwang NO.1 Coal Mine, a variety of gob closure design schemes and gob gas drainage design schemes are put forward, and the field effect investigation scheme is given. After the tunnels and open-off cut of the test coal mine’s first mining face are connected, under the guidance of the above research results, the field blasting test and the 110 mining method entry-retaining test are further carried out to verify the rationality of the design of the roof-cutting parameters and the feasibility of the gangue wall closure and gas drainage design. Furthermore, in the process of the field practice, continuous research is carried out on the stope pressure law and the adjacent layer gas drainage technology under the 110 mining method, and finally, the 110 mining method application technology system in the Diandong Mining Area is formed. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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15 pages, 3151 KiB

Open AccessArticle

Classification of Coal Bursting Liability Based on Support Vector Machine and Imbalanced Sample Set

by Yuefeng Li, Chao Wang and Yv Liu

Minerals 2023, 13(1), 15; https://doi.org/10.3390/min13010015 - 23 Dec 2022

Cited by 9 | Viewed by 2310

Abstract

As an inherent property of the accumulation of elastic energy and the sudden instability failure of coal, coal bursting liability (CBL) is the basis of the research on the early warning and prevention of coal burst. To accurately classify the CBL level, the [...] Read more.

As an inherent property of the accumulation of elastic energy and the sudden instability failure of coal, coal bursting liability (CBL) is the basis of the research on the early warning and prevention of coal burst. To accurately classify the CBL level, the support-vector-machine (SVM) method was introduced in this paper, and the dynamic failure time (DT), elastic energy index (W_ET), impact energy index (K_E) and uniaxial compressive strength (R_C) were selected as the classification indexes. An imbalanced sample set, containing 95 groups of measured data of CBL, was established, and eight SVM classification models were constructed, based on different kernel functions and swarm-intelligence-optimization algorithms. Focusing on the problem of sample imbalance, the classification accuracy, A, F1-score and kappa coefficient were used to comprehensively evaluate the classification performance of SVM models, and the grey-wolf-optimizer SVM (GWO-SVM) model was selected as the best model in this paper, reaching the highest accuracy of 98.9%. The GWO-SVM was applied to identify the CBL level of the 4# coal seam in Xiaozhuang Coal Mine and the 1# coal seam in the Wanfeng Coal Mine. The results of the engineering application are consistent with those from the engineering field, and show that the proposed model is scientific and practical, and can be a new method for CBL classification. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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22 pages, 5134 KiB

Open AccessArticle

Applying Machine Learning and Automatic Speech Recognition for Intelligent Evaluation of Coal Failure Probability under Uniaxial Compression

by Honglei Wang, Zhenlei Li, Dazhao Song, Xueqiu He and Majid Khan

Minerals 2022, 12(12), 1548; https://doi.org/10.3390/min12121548 - 30 Nov 2022

Cited by 2 | Viewed by 1904

Abstract

Acoustic emission (AE) monitoring is an effective tool to quantify the dynamic damage that may cause heavy casualties and huge property losses in rock engineering. Instead of traditional failure evaluation methods, in this paper, the coal failure mechanism is evaluated in a complicated [...] Read more.

Acoustic emission (AE) monitoring is an effective tool to quantify the dynamic damage that may cause heavy casualties and huge property losses in rock engineering. Instead of traditional failure evaluation methods, in this paper, the coal failure mechanism is evaluated in a complicated geological environment under uniaxial compression tests by employing machine learning (ML) and automatic speech recognition (ASR). Taking advantage of the ASR technology, the Mel-frequency cepstrum coefficients (MFCC) were extracted as sample features, while ML was used to paradigm the artificial intelligent evaluation of the failure probability of coal (AIEFPC). Additionally, the five-fold cross-validation method was used to assess the AIEFPC predictive effect incorporating cumulative hits number, cumulative ring count, and amplitude as sample features. The influence of category weight on the prediction effect of AIEFPC on a different category of sample sets has been discussed and analyzed. The results show that AIEFPC has the potential to use the MFCC of the 40 ms AE segment at any time to predict the dangerous state of the coal sample with a prediction accuracy of >85%. The probability value of the hazardous samples is computed through AIEFPC that further helped in evaluating the reliability of the prediction results. It is inferred from the obtained results that a larger category weight value of the hazardous samples can improve the prediction accuracy of AIEFPC than the safe sample. This research provides a new way of effectively predicting the coal failure probability before the damage and failure that can be applied to worldwide case-studies. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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20 pages, 6371 KiB

Open AccessArticle

Acoustic Emission Parameter Characterization of Damage Process of the Limestone with Different Rockburst Tendencies

by He Zhang, Qinglin Chen, Xiaojun Wang, Kui Zhao and Qiang Zeng

Minerals 2022, 12(11), 1423; https://doi.org/10.3390/min12111423 - 10 Nov 2022

Cited by 6 | Viewed by 1676

Abstract

The laboratory discrimination tests of the rockburst tendency and AE tests under the uniaxial compression were conducted on the limestone. Three criterions were used to judge the rockburst tendency of the limestone with a buried depth of 600–1000 m under the same borehole. [...] Read more.

The laboratory discrimination tests of the rockburst tendency and AE tests under the uniaxial compression were conducted on the limestone. Three criterions were used to judge the rockburst tendency of the limestone with a buried depth of 600–1000 m under the same borehole. The rock damages were quantified by the AE events, ring count and energy. The fractal characteristics of these parameters were compared and analyzed. The characterization accuracy of these parameters on the damage process of the limestone with different rockburst tendencies was discussed. The AE parameters of the limestone with different rockburst tendencies increase sharply when the stress is near its peak. With the increase in the rockburst tendency, the variation of the AE event rate and ring count of the limestone is more and more consistent with the AE energy. Based on the characterization of the AE events and ring count, the damage process is characterized by a gradual evolution, while based on the energy characterization, it is characterized by a stepped evolution. The damage represented by the AE energy reveals the intensity and instantaneity of the rockburst failure. According to the verification of the CV value, the fractal dimension D of the AE energy fluctuates more gently with the increase in the rockburst tendency. It reflects the energy storage characteristics of the rock with a rockburst tendency in the loading process, which is consistent with the failure mechanism of the rockburst. Therefore, AE energy is more accurate to characterize and predict the failure of the limestone with a rockburst tendency. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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23 pages, 9955 KiB

Open AccessArticle

Application Study of Empirical Wavelet Transform in Time–Frequency Analysis of Electromagnetic Radiation Induced by Rock Fracture

by Quan Lou, Xiangyun Wan, Bing Jia, Dazhao Song, Liming Qiu and Shan Yin

Minerals 2022, 12(10), 1307; https://doi.org/10.3390/min12101307 - 17 Oct 2022

Cited by 9 | Viewed by 2363

Abstract

The time–frequency characteristics of electromagnetic radiation (EMR) waveform induced by rock fracture are very important to the monitoring and early–warning using the EMR method for the mine rockburst. The empirical wavelet transform (EWT), as a waveform time–frequency analysis method, has the advantages of [...] Read more.

The time–frequency characteristics of electromagnetic radiation (EMR) waveform induced by rock fracture are very important to the monitoring and early–warning using the EMR method for the mine rockburst. The empirical wavelet transform (EWT), as a waveform time–frequency analysis method, has the advantages of a clear theoretical basis, convenient calculation, and no modal aliasing. To apply EWT to the field of EMR time–frequency analysis, the operation of Fourier axis segmentation of EWT is improved. In detail, the adaptive selection method for a window width of closing operation and the adaptive determination method of segment number of Fourier axis are proposed for EWT. The Fourier axis obtained by short–time Fourier transform (STFT) is used in the EWT process, rather than that obtained by discrete Fourier transform (DFT), taking a better Fourier axis segmentation effect. The improved EWT together with Hilbert transform (HT) applied to the time–frequency analysis for the EMR waveform of rock fracture, and the time–frequency spectrum obtained by EWT–HT can well describe the time–frequency evolution characteristics. Compared with STFT and Hilbert–Huang transform (HHT), EWT–HT has significant advantages in time–frequency resolution and overcoming modal aliasing, providing a powerful tool for time–frequency analysis for the EMR waveform induced by rock fracture. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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20 pages, 88266 KiB

Open AccessArticle

A Dynamic Coupled Elastoplastic Damage Model for Rock-like Materials Considering Tension-Compression Damage and Pressure-Dependent Behavior

by Xuelong Hu, Ming Zhang, Wenyao Xu, Min Tu, Zhiqiang Yin and Xiangyang Zhang

Minerals 2022, 12(7), 851; https://doi.org/10.3390/min12070851 - 2 Jul 2022

Cited by 5 | Viewed by 2386

Abstract

A dynamic coupled elastoplastic damage model for rock-like materials is proposed. The model takes unified strength theory as the strength criterion. To characterize the different damage between compression and tension, two damage variables both in compression and in tension are introduced into the [...] Read more.

A dynamic coupled elastoplastic damage model for rock-like materials is proposed. The model takes unified strength theory as the strength criterion. To characterize the different damage between compression and tension, two damage variables both in compression and in tension are introduced into the model. The former is represented by the generalized shear plastic strain and volumetric plastic strain and the latter is expressed with the generalized shear plastic strain. Furthermore, the model takes the strain rate effect into account to reflect the strength enhancement under dynamic loading. Because of the difference in plastic hardening between compression and tension, a modified hardening function is adopted. At the same time, the volume strain from HJC model is modified to be consistent with one of continuum mechanics. The developed model is numerically implemented into LS-DYNA with a semi-implicit algorithm through a user-defined material interface (UMAT). The reliability and accuracy of the developed model are verified by the simulation of four basic experiments with different loading conditions. The proposed model was found to be applicable to different mechanical behaviors of rock-like materials under static and dynamic loading conditions. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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18 pages, 4430 KiB

Open AccessArticle

Mechanical Properties and Acoustic Emission Characteristics of Unloading Instability of Sandstone under High Stress

by Zhiyuan Hou, Fukun Xiao, Gang Liu, Oleg Viktorovich Bashkov and Lan Lyu

Minerals 2022, 12(6), 722; https://doi.org/10.3390/min12060722 - 5 Jun 2022

Cited by 7 | Viewed by 2059

Abstract

In order to analyze the law of unloading instability of deep rock mass, the unloading experiment of sandstone under different confining pressures was carried out, and the mechanical properties and acoustic emission characteristics of sandstone unloading failure under high stress were obtained. The [...] Read more.

In order to analyze the law of unloading instability of deep rock mass, the unloading experiment of sandstone under different confining pressures was carried out, and the mechanical properties and acoustic emission characteristics of sandstone unloading failure under high stress were obtained. The results demonstrate that before unloading, the sandstone under low stress shows compression and elastic deformation, whereas that under high stress shows elastic deformation and plastic deformation. Moreover, the unloading behavior of sandstone under low stress is ductile, whereas that under high stress is brittle. Poisson’s ratio and elastic modulus have negative and positive correlation with initial confining pressure, respectively. During unloading, the higher the initial confining pressure is, the earlier the rock sample damage occurs. Prior to the accelerated damage stage, the unloading amount and AE cumulative count are inversely proportional and directly proportional to the initial confining pressure, respectively. The simultaneous occurrence of UHF, HF, MF, and LF in the AE power spectrum, as well as a steep increase in fractal dimension followed by a decrease, can be used as precursors to unloading instability in sandstone. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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11 pages, 3529 KiB

Open AccessArticle

Integration of Seismic Refraction and Fracture-Induced Electromagnetic Radiation Methods to Assess the Stability of the Roof in Mine-Workings

by Sergei Daniliev, Natali Danilieva, Sergei Mulev and Vladimir Frid

Minerals 2022, 12(5), 609; https://doi.org/10.3390/min12050609 - 12 May 2022

Cited by 18 | Viewed by 2298

Abstract

This paper considers the joint use of two popular geophysical methods (fracture-induced electromagnetic radiation and seismic refraction tomography) to assess the stress-state in underground mine-workings. Such a combination of two indirect methods allows the identification of zones of increased stress in the rock [...] Read more.

This paper considers the joint use of two popular geophysical methods (fracture-induced electromagnetic radiation and seismic refraction tomography) to assess the stress-state in underground mine-workings. Such a combination of two indirect methods allows the identification of zones of increased stress in the rock along the axis of the mine-workings, and zones of intense weakening or disintegration in the rock massif above the roof of the mine-workings. The measurements of longitudinal and compressive wave speeds were used to calculate 2D sections of Young’s modulus and Poisson’s ratio to assess the rock mechanical properties in the vicinity of the mine-workings. It is shown that the anomalies of both elastic parameters correspond to those of fracture-induced electromagnetic radiation. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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16 pages, 9180 KiB

Open AccessArticle

Dynamic Propagation and Electro-Mechanical Characteristics of New Microcracks in Notched Coal Samples Studied by the Three-Point Bending Test System and AFM

by Weixiang Wang, Dazhao Song, Xueqiu He, Qingxia Liu, Zhenlei Li, Liming Qiu and Guodong Mei

Minerals 2022, 12(5), 582; https://doi.org/10.3390/min12050582 - 5 May 2022

Cited by 2 | Viewed by 1903

Abstract

This work extends research on the mechanism of electromagnetic radiation (EMR) induced by coal or rock fractures to the category of microscopic dynamic experimental research. A custom-made three-point bending test system and atomic force microscope (AFM) were integrated to obtain the microdynamic loading [...] Read more.

This work extends research on the mechanism of electromagnetic radiation (EMR) induced by coal or rock fractures to the category of microscopic dynamic experimental research. A custom-made three-point bending test system and atomic force microscope (AFM) were integrated to obtain the microdynamic loading test system. The notched coal samples were prepared specially. The dynamic propagation of new microcracks in coal samples was measured, and the propagation velocity was calculated. The morphology and electro-mechanical characteristics of new microcracks were tested. More importantly, the causes of the changes in the electro-mechanical characteristics before and after fracture were analyzed, and the effects of these changes on the EMR were discussed. The results showed that the average propagation velocities during the same time interval are 9.5 μm/s, 12.1 μm/s, and 16.2 μm/s. The elastic modulus of the material at the microcrack edge is generally smaller than that of the material in other locations, while the adhesion and deformation are larger. Moreover, the closer the material is to the microcrack, the higher its surface potential. The electrons generated at the microcrack edge and emitted into the atmosphere, which made the greater potentials of the microcrack edge. Many electrons with different velocities and directions migrate in similar parallel-plate capacitors, which are formed by the relative microscale surface of the coal microcrack tip and have different field strengths, resulting in EMR with complex frequencies and different intensities. This study provides a micro-dynamic experimental basis for research on the electromagnetic radiation mechanism. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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16 pages, 4383 KiB

Open AccessArticle

Characterization of Overburden Deformation and Subsidence Behavior in a Kilometer Deep Longwall Mine

by Manoj Khanal, Qingdong Qu, Yiran Zhu, Jianlin Xie, Weibing Zhu, Tao Hou and Shikang Song

Minerals 2022, 12(5), 543; https://doi.org/10.3390/min12050543 - 27 Apr 2022

Cited by 18 | Viewed by 2493

Abstract

A thorough understanding of mining-induced overburden deformation characteristics and the associated stress redistributions are essential to effectively manage complex safety and environmental issues that arise from underground mining. This is particular for mining in deep environments. This paper presents a numerical modelling study [...] Read more.

A thorough understanding of mining-induced overburden deformation characteristics and the associated stress redistributions are essential to effectively manage complex safety and environmental issues that arise from underground mining. This is particular for mining in deep environments. This paper presents a numerical modelling study on a kilometer-deep longwall coal mine where a thick sandstone aquifer is situated approximately 200 m above the working seam. The mine adopts a special mine layout with narrow and wide pillars between longwalls and areas to manage water inrush and coal burst risks. The modelling results show that overburden deformation stops at a certain height, above which the displacement profile over multiple longwall panels become nearly flat. Increasing panel width and extraction height lead to a greater extent of the fractured zone and a larger magnitude of surface subsidence. An extraction height of more than 7 m may breach the thick aquifer. Stress concentration on the wide pillar can undergo up to 5 times increase in the in-situ stress, posing high risks of coal burst. Adjusting mining parameters such as panel width and extraction height can facilitate an effective strategy to minimize water inrush and coal burst risks in such a mining condition. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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14 pages, 4217 KiB

Open AccessArticle

Application of MEMS-Based Accelerometers for Near-Field Monitoring of Blasting-Induced Seismicity

by Krzysztof Fuławka, Piotr Mertuszka, Marcin Szumny, Lech Stolecki and Krzysztof Szczerbiński

Minerals 2022, 12(5), 533; https://doi.org/10.3390/min12050533 - 25 Apr 2022

Cited by 12 | Viewed by 3111

Abstract

Proper monitoring of seismic risk and reliable evaluation of destress blasting efficiency requires a well-developed seismic network surrounding the analyzed area. Unfortunately, the construction of a dense seismic monitoring system using standard types of seismometers and accelerometers is associated with high costs of [...] Read more.

Proper monitoring of seismic risk and reliable evaluation of destress blasting efficiency requires a well-developed seismic network surrounding the analyzed area. Unfortunately, the construction of a dense seismic monitoring system using standard types of seismometers and accelerometers is associated with high costs of seismic network development and maintenance. Significant improvements in this regard may be potentially achieved by replacing expensive monitoring devices with other cost-effective sensors such as MEMS-based accelerometers. Nevertheless, this topic has not been sufficiently investigated yet, and the usefulness of such devices for monitoring seismicity in deep underground mines has not been recognized. The goal of this paper was to perform preliminary measurements of blasting-induced seismicity in the near-wave field with the use of a single three-axial MEMS-based accelerometer and three uniaxial seismometers. The collected seismic records induced by multi-face blasting were compared in time and frequency domains. In the time domain, the values of 3D peak motion plots were analyzed, and the possibility of identification of subsequent delay times in recorded waveforms was investigated. In the case of frequency distribution, the Power Spectrum Density plots were calculated and compared. The results of the analysis proved that MEMS-based accelerometers provide reliable results and may be successfully implemented for regular use in underground seismic monitoring systems. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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17 pages, 5557 KiB

Open AccessArticle

Core Orientation Technology Based on Drilling Trajectory Projection and Its Application in In Situ Stress Measurement of the Deepest Shaft in China

by Chunde Ma, Guanshuang Tan, Xibing Li, Jiaqing Xu and Jiangzhan Chen

Minerals 2022, 12(5), 521; https://doi.org/10.3390/min12050521 - 22 Apr 2022

Cited by 2 | Viewed by 3523

Abstract

Deep borehole cores are an important material basis for understanding deep stress conditions and rockburst risk; however, the complex environment of deep boreholes poses many challenges to traditional core orientation techniques, thus limiting the application of cores in fields such as in situ [...] Read more.

Deep borehole cores are an important material basis for understanding deep stress conditions and rockburst risk; however, the complex environment of deep boreholes poses many challenges to traditional core orientation techniques, thus limiting the application of cores in fields such as in situ stress measurement. A technical method of restoring the original spatial attitude of nonoriented geological cores on the ground was proposed based on the inherent “trajectory projection consistency” relationship between the borehole and the corresponding core. A prototype machine of core ground reorientation was developed. Using this method and machine, ground reorientation was performed on cores drilled from the deepest shaft in China. Subsequently, the reoriented core acoustic emission (AE) method was conducted to identify the in situ stress within the project area. Meanwhile, measurement accuracy was verified by the stress relief method. The results show that the in situ stress distributions, including the azimuth and the trends in principal stresses by the two methods, are in good agreement and indicate that the historical maximum principal stress in the case of the mine has little abrupt variability with that of the present day. The research results can be used as the design basis for the safe construction of the deepest shaft. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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16 pages, 5070 KiB

Open AccessArticle

An Experimental Study: Variation Law of Magnetic Field around Concrete during Loading

by Liming Qiu, Yongjun Tong, Jie Li, Dazhao Song, Man Wang and Shan Yin

Minerals 2022, 12(4), 399; https://doi.org/10.3390/min12040399 - 24 Mar 2022

Cited by 6 | Viewed by 2375

Abstract

In order to reveal the magnetic field response law and mechanism of concrete under load, the variation law of magnetic field intensity (MFI) of concrete samples under uniaxial loading, graded loading and cyclic loading was tested, and the field application scenarios of magnetic [...] Read more.

In order to reveal the magnetic field response law and mechanism of concrete under load, the variation law of magnetic field intensity (MFI) of concrete samples under uniaxial loading, graded loading and cyclic loading was tested, and the field application scenarios of magnetic field monitoring technology are proposed. The results showed that a magnetic field signal would be generated during the loading failure process of the concrete sample, which was accompanied by the whole loading process. In the uniaxial compression process, MFI showed a steady increase trend, but it would increase rapidly when the load drop occurred in the sample. The stronger the rupture, the more significant the change of MFI. MFI was not linearly proportional to the amount of change in the load drop. MFI around the concrete sample was positively correlated with the load. When the concrete was in the constant load stage, MFI around the concrete remained basically stable. When the main rupture of the concrete sample occurred, MFI reached a peak value, it did not keep at a high level all the time, but decreased rapidly. There are two mechanisms for the generation of the magnetic field in the process of concrete failure under load, namely the piezomagnetic effect and the friction effect, which correspond to the action of the load and the excitation of the fracture, respectively. The former causes the stable increase of MFI, and the effect is related to the influence of the content of the piezoelectric magnetic material in the material composition; the latter leads to a sudden increase of MFI, and the effect is related to the triboelectric effect of the micro-particles of the material. The research results are conducive to the accurate prediction of the concrete magnetic field monitoring, and help promote the development of mine dynamic disaster monitoring and early warning technology. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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19 pages, 4501 KiB

Open AccessArticle

Orthogonal Numerical Analysis of Deformation and Failure Characteristics of Deep Roadway in Coal Mines: A Case Study

by Xiaojun Feng, Zeng Ding, Qinjing Hu, Xue Zhao, Muhammad Ali and Jefferson T. Banquando

Minerals 2022, 12(2), 185; https://doi.org/10.3390/min12020185 - 30 Jan 2022

Cited by 29 | Viewed by 3199

Abstract

With the development of deep, underground coal mines in China, the failure mechanism of the rocks surrounding roadways is becoming increasingly complicated and the deformational control is also significantly difficult. In this study, based on the temporal and spatial deformational distribution of the [...] Read more.

With the development of deep, underground coal mines in China, the failure mechanism of the rocks surrounding roadways is becoming increasingly complicated and the deformational control is also significantly difficult. In this study, based on the temporal and spatial deformational distribution of the deep roadway area in the 2233 working face of Fuxin Hengda Coal Mine, factors affecting the deformation and failure mechanism of deep-buried roadways, such as cohesion (c), tensile strength (

σ_{t}

), internal friction angle (φ), vertical ground stress (p), and the horizontal-to-vertical stress ratio (λ), were analyzed using orthogonal numerical experiments. The stress and electromagnetic radiation monitoring data were used to locate areas of highly concentrated deformation in the roadway and surrounding rocks. The results show that the order of the degree of influence of the surrounding rock and geometric parameters on the deformation of the deep-buried roadway is φ > p >

σ_{t}

> λ > c. The vertical stress of the roof and the horizontal stress of the two sides are negatively correlated with the tensile strength and horizontal-to-vertical stress ratio, respectively, and mainly shear failure occurs in the area. The higher the level of the surrounding rock, the more serious is the deterioration and deformation. The electromagnetic radiation reflects the distribution range of the high-stress concentration area and strength deterioration area. The test results accurately describe the deformation–deterioration-failure laws of rock surrounding deep-buried roadways influenced by different factors. The results are of great significance for analyzing the deformation and failure characteristics of rocks surrounding roadways, preventing rockburst, and supporting the parameter optimization of roadways. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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17 pages, 5232 KiB

Open AccessArticle

Study on the Nonlinear Characteristics of EMR and AE during Coal Splitting Tests

by Liming Qiu, Yi Zhu, Dazhao Song, Xueqiu He, Weixiang Wang, Yang Liu, Yuzhe Xiao, Menghan Wei, Shan Yin and Qiang Liu

Minerals 2022, 12(2), 108; https://doi.org/10.3390/min12020108 - 19 Jan 2022

Cited by 57 | Viewed by 3037

Abstract

Coal and rock dynamic disasters have been the main concern in underground engineering because these seriously threaten the safety of miners and industrial production. Aiming to improve the EMR and AE monitoring technology, the refined nonlinear characteristics of EMR and AE during coal [...] Read more.

Coal and rock dynamic disasters have been the main concern in underground engineering because these seriously threaten the safety of miners and industrial production. Aiming to improve the EMR and AE monitoring technology, the refined nonlinear characteristics of EMR and AE during coal splitting failure are studied using Hilbert-H and multifractal theory, and valuable information pertaining to coal fracture law contained in EMR and AE waveform was revealed. The results show that the EMR and AE of coal splitting failure are related to the process of coal crack propagation. They possess the same initiation time and frequency band, however, the signal duration of EMR is comparatively longer than AE, and the main frequency of AE is higher than EMR. The EMR of coal splitting failure has the same excitation source as AE; nonetheless, the excited forms display different behavior. In terms of signal duration, the distribution of EMR signal is relatively uniform, the proportion of large-signal is less, the amount of information is more than that of AE, and the multifractal characteristics are more complicated. During the coal splitting failure, AE is mainly generated in the process of wall vibration caused by crack propagation, while the generation of EMR includes piezoelectric effect, charge separation, free charge vibration, charge neutralization and other processes, making EMR more complicated than AE and has a relatively low frequency. The research provides an effective method for studying nonlinear refinement characteristics of coal EMR and AE, and can provide an important basis for the study of the mechanism of EMR generation. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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19 pages, 6138 KiB

Open AccessArticle

Discrimination of Different AE and EMR Signals during Excavation of Coal Roadway Based on Wavelet Transform

by Baolin Li, Zhonghui Li, Enyuan Wang, Nan Li, Jing Huang, Youcang Ji and Yue Niu

Minerals 2022, 12(1), 63; https://doi.org/10.3390/min12010063 - 3 Jan 2022

Cited by 14 | Viewed by 2075

Abstract

During the process of coal road excavation, various interference signals, induced by environmental noise, drilling, and scraper loader, will affect the risk assessment of coal and gas outburst using acoustic emission (AE) and electromagnetic radiation (EMR) monitoring technology. To distinguish between different interference [...] Read more.

During the process of coal road excavation, various interference signals, induced by environmental noise, drilling, and scraper loader, will affect the risk assessment of coal and gas outburst using acoustic emission (AE) and electromagnetic radiation (EMR) monitoring technology. To distinguish between different interference signals and danger signals, discrete wavelet transform (DWT) was used to decompose and reconstruct signals, and continuous wavelet transform (CWT) was used to obtain the time-frequency plane. The research results show that: (1) interference signals generally exhibit fluctuating changes within small ranges; in comparison, the intensity of AE and EMR signals caused by coal and rock fracture is found to continuously rise for a long period (longer than 2 h). (2) Different interference signals and danger signals differ significantly in their time-frequency plane. (3) Through decomposition and reconstruction of original signal, obvious precursor information can be found in the time-frequency plane of reconstructed signals. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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23 pages, 11295 KiB

Open AccessArticle

Numerical Investigation on Influence of Two Combined Faults and Its Structure Features on Rock Burst Mechanism

by Anye Cao, Yaoqi Liu, Siqi Jiang, Qi Hao, Yujie Peng, Xianxi Bai and Xu Yang

Minerals 2021, 11(12), 1438; https://doi.org/10.3390/min11121438 - 19 Dec 2021

Cited by 14 | Viewed by 3510

Abstract

With the increase in coal mining depth, engineering geological conditions and the stress environment become more complex. Many rock bursts triggered by two combined faults have been observed in China, but the mechanism is not understood clearly. The focus of this research aims [...] Read more.

With the increase in coal mining depth, engineering geological conditions and the stress environment become more complex. Many rock bursts triggered by two combined faults have been observed in China, but the mechanism is not understood clearly. The focus of this research aims at investigating the influence of two combined faults on rock burst mechanisms. The six types of two combined faults were first introduced, and two cases were utilized to show the effects of two combined faults types on coal mining. The mechanical response of the numerical model with or without combined faults was compared, and a conceptual model was set up to explain the rock burst mechanism triggered by two combined faults. The influence of fault throw, dip, fault pillar width, and mining height on rock burst potential was analyzed. The main control factors of rock burst in six models that combined two faults were identified by an orthogonal experiment. Results show that six combinations of two faults can be identified, including stair-stepping fault, imbricate fault, graben fault, horst fault, back thrust fault, and ramp fault. The particular roof structure near the two combined faults mining preventing longwall face lateral abutment pressure from transferring to deep rock mass leads to stress concentration near the fault areas. Otherwise, a special roof structure causing the lower system stiffness of mining gives rise to the easier gathering of elastic energy in the coal pillars, which makes it easier to trigger a rock burst. There is a nonlinear relationship between fault parameters and static or dynamic load for graben faults mining. The longwall face has the highest rock burst risk when the fault throw is between 6 and 8 m, the fault dip is larger than 65°, the mining height is greater than 6 m, and the coal pillar width is less than 50 m. The stair-stepping, imbricate, horst, and ramp fault compared to the other fault types will produce higher dynamic load stress during longwall retreat. Fault pillar width is the most significant factor for different two combined faults, leading to the rise of static load stress and dynamic proneness. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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20 pages, 20675 KiB

Open AccessArticle

Investigation on the Failure Mechanism of Weak Floors in Deep and High-Stress Roadway and the Corresponding Control Technology

by Dong Zhang, Jianbiao Bai, Shuai Yan, Rui Wang, Ningkang Meng and Gongyuan Wang

Minerals 2021, 11(12), 1408; https://doi.org/10.3390/min11121408 - 12 Dec 2021

Cited by 15 | Viewed by 3420

Abstract

Large deformation of roadway and floor burst are the two major geotechnical hazards encountered with high mining stress in deep mines. In this paper, the stress and energy conditions generated by the impact damage on the rock surrounding a roadway are analyzed, and [...] Read more.

Large deformation of roadway and floor burst are the two major geotechnical hazards encountered with high mining stress in deep mines. In this paper, the stress and energy conditions generated by the impact damage on the rock surrounding a roadway are analyzed, and UDEC software was used to study the deformation characteristics of the roadway, as well as its failure mechanism under the influence of superimposed dynamic and static loads. The results indicate that the soft floor of a deep-buried roadway has a high damage degree and an obvious stress release effect, high static load leads to slow floor heave, and strong dynamic load disturbance is the principal trigger leading to floor burst. In addition, the anisotropy caused by the bedding surface weakens the cooperative characteristics of the support system, resulting in serious instability of the whole rock surrounding the roadway. Full-section anchor cables and inverted arches were adopted to maintain the stability of the rock surrounding the roadway. The monitoring results obtained from field tests show that the adoption of the combined support system effectively avoids floor burst caused by the superposition of dynamic and static loads; the maximum floor heave is 67.9 mm, which is 95% lower than the original value, ensuring safety in coal mining operations. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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18 pages, 7018 KiB

Open AccessArticle

Study on the Modification of Confining Rock for Protecting Coal Roadways against Impact Loads from a Roof Stratum

by Haiyang Yi, Zhenhua Ouyang, Xinxin Zhou, Zhengsheng Li, Jianqiang Chen, Kang Li and Kunlun Liu

Minerals 2021, 11(12), 1331; https://doi.org/10.3390/min11121331 - 28 Nov 2021

Cited by 4 | Viewed by 2091

Abstract

Promoting the ability of anti-bursting of the confining rock of a coal roadway is of significant importance to the safe production of a coal mine. In particular, in deep-buried coal mines, highly frequent rock burst occurs due to large earth pressure and complex [...] Read more.

Promoting the ability of anti-bursting of the confining rock of a coal roadway is of significant importance to the safe production of a coal mine. In particular, in deep-buried coal mines, highly frequent rock burst occurs due to large earth pressure and complex geological conditions, which needs serious improvement. This paper investigated a type of confining rock modified method, which can modify the physical properties of the surrounding rock and form a crack region and a reinforced region by blasting and grouting reinforcement. Based on a set of physical model experiments and numerical modeling, the results of a comparative analysis between a normal roadway and the modified roadway in the static stress redistribution, dynamic stress, damage evolution, and energy dissipation suggest that the modified confining rock is capable of protecting the coal roadway against rock burst from roof stratum, obviously reducing and transferring the concentered static–dynamic stress out of the cracked region, dissipating the dynamic energy by plastic damage in the cracked region, and keeping the integrity of the reinforced region. In addition, the velocity of the dynamic stress vibration wave at the surface of the modified coal roadway is obviously reduced, which is beneficial for decreasing the movement of cracked rock blocks and protecting the lives and goods in the coal roadway. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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15 pages, 1456 KiB

Open AccessArticle

An Intelligent Rockburst Prediction Model Based on Scorecard Methodology

by Honglei Wang, Zhenlei Li, Dazhao Song, Xueqiu He, Aleksei Sobolev and Majid Khan

Minerals 2021, 11(11), 1294; https://doi.org/10.3390/min11111294 - 22 Nov 2021

Cited by 8 | Viewed by 2864

Abstract

Rockburst is a serious hazard in underground engineering, and accurate prediction of rockburst risk is challenging. To construct an intelligent prediction model of rockburst risk with interpretability and high accuracy, three binary scorecards predicting different risk levels of rockburst were constructed using ChiMerge, [...] Read more.

Rockburst is a serious hazard in underground engineering, and accurate prediction of rockburst risk is challenging. To construct an intelligent prediction model of rockburst risk with interpretability and high accuracy, three binary scorecards predicting different risk levels of rockburst were constructed using ChiMerge, evidence weight theory, and the logistic regression algorithm. An intelligent rockburst prediction model based on scorecard methodology (IRPSC) was obtained by integrating the three scorecards. The effects of hazard sample category weights on the missed alarm rate, false alarm rate, and accuracy of the IRPSC were analyzed. Results show that the accuracy, false alarm rate, and missed alarm rate of the IRPSC for rockburst prediction in riverside hydropower stations are 75%, 12.5%, and 12.5%, respectively. Setting higher hazard sample category weights can reduce the missed alarm rate of IRPSC, but it will lead to a higher false alarm rate. The IRPSC can adaptively adjust the threshold and weight value of the indicator and convert the abstract machine learning model into a tabular form, which overcomes the commonly black box problems of machine learning model, as well as is of great significance to the application of machine learning in rockburst risk prediction. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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24 pages, 15272 KiB

Open AccessArticle

Borehole-Based Monitoring of Mining-Induced Movement in Ultrathick-and-Hard Sandstone Strata of the Luohe Formation

by Xiaozhen Wang, Weibing Zhu, Jianlin Xie, Hongkai Han, Jingmin Xu, Zhongyi Tang and Jialin Xu

Minerals 2021, 11(11), 1157; https://doi.org/10.3390/min11111157 - 21 Oct 2021

Cited by 5 | Viewed by 2542

Abstract

Water outbursts and rock bursts often occur during the mining of coal seams under water-rich sandstone strata with thicknesses exceeding 50 m, otherwise called ultrathick-and-hard strata (UTHS), which are common throughout the mining areas of northwestern China. It is important to understand the [...] Read more.

Water outbursts and rock bursts often occur during the mining of coal seams under water-rich sandstone strata with thicknesses exceeding 50 m, otherwise called ultrathick-and-hard strata (UTHS), which are common throughout the mining areas of northwestern China. It is important to understand the behaviors of their movement and the evolution of their internal fractures to inform the formulation of effective disaster prevention. Due to the presence of the Luohe Formation UTHS in the overburden of the Tingnan Coal Mine in the Binchang mining area and the powerful mining-induced pressure (MIP) events that occurred during the excavation of Panel #2, the internal strata movement of the overburden and the evolution of its fractures were monitored in situ by fiber optic and multipoint borehole extensometers (MPBX) during the excavation of Working Face #207. It was found that a large number of ring-shaped fractures were observed at 24.8–81 m above the lower boundary of the Luohe Formation—in areas above the goaf of Working Face #206—before Working Face #207 was mined. When Working Face #207 was mined, the fractures that were originally located in the deep strata of the Luohe Formation started to close and migrate towards shallow strata. Crack closure and migration were also observed during the monitoring of internal strata movement. Furthermore, the final displacements of Y1-1-1#, Y1-2-2#, and Y1-2-3# relative to the surface were 77, 248, and 134 mm, which were very small relative to the surface subsidence of 1380 mm. It was found that mining-induced perturbations caused the Luohe Formation UTHS to subside continuously and no risk of a large and sudden break would occur in the Luohe Formation UTHS during the mining of Working Face #207. The results of this study provide important data for the safety of mining operations at Working Face #207, which were validated by microseismic monitoring during the mining of it. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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Review

Jump to: Research

17 pages, 2202 KiB

Open AccessFeature PaperReview

Evaluating the Application of Rock Breakage without Explosives in Underground Construction—A Critical Review of Chemical Demolition Agents

by Kelly-Meriam Habib, Shahé Shnorhokian and Hani Mitri

Minerals 2022, 12(2), 220; https://doi.org/10.3390/min12020220 - 9 Feb 2022

Cited by 24 | Viewed by 8131

Abstract

The method of drilling and blasting with explosives is widely used in rock fragmentation applications in underground construction projects, such as tunnels and caverns. However, the use of explosives is associated with rigorous safety and environmental constraints, since blasting creates toxic fumes, ground [...] Read more.

The method of drilling and blasting with explosives is widely used in rock fragmentation applications in underground construction projects, such as tunnels and caverns. However, the use of explosives is associated with rigorous safety and environmental constraints, since blasting creates toxic fumes, ground vibrations, and dust. Because of these constraints, there has been a growing interest in transitioning away from explosives-based rock fragmentation. The use of explosives-free methods could lead to continuous operation by eliminating the need for idle time with additional ventilation required to exhaust the blast fumes. This paper first presents a critical review of various methods that have been developed so far for rock fragmentation without explosives. Such methods include thermal fragmentation, plasma blasting, controlled foam injection, radial-axial splitter, and supercritical carbon dioxide. Thermal fragmentation, as the name implies, uses high heat to spall high-grade ore. However, it requires high heat energy, which requires additional ventilation as compared to normal conditions to cool the work area. Plasma blasting uses a high temperature and pressure plasma to fracture rock in a safe manner. While this method may be environmentally friendly, its usage may significantly slow tunnel development due to the need to haul one or more large energy capacitor banks into and out of the work area repeatedly. Controlled foam injection is another chemical method, whereby foam is the medium for fracturing. Although claimed to be environmentally friendly, it may still pose safety risks such as air blast or flyrock due to its dynamic nature. A radial-axial splitter (RASP) is an instrument specially designed to fracture a borehole in the rock face but only at the pace of one hole at a time. Supercritical carbon dioxide is used with the equipment designed to provide a high-pressure jet stream to fracture rock, and replaces water in these instruments. The method of soundless chemical demolition agents (SCDA) is evaluated in more detail and its merits over others are highlighted, making it a potentially viable alternative to blasting with explosives in underground excavation applications. Future work involves the optimization of SCDA for implementation in underground mines. The discussion compares the key features and limitations, and future work needs are underlined. Full article

(This article belongs to the Special Issue Rockburst Mechanism and Its Prevention and Control in Underground Mines)

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