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16 pages, 5373 KiB

Open AccessArticle

Evolution Model of Coal Failure Using Energy Dissipation under Cyclic Loading/Unloading

by Chunlai Wang, Chang Zuo and Ze Zhao

Appl. Sci. 2023, 13(9), 5797; https://doi.org/10.3390/app13095797 - 8 May 2023

Cited by 3 | Viewed by 1236

Abstract

The damage and fracture of coal is accompanied by a complex energy conversion process, and these different stages of energy evolution are closely related to coal failure. In this paper, an evolution model describing the behavior of coal failure was proposed using the [...] Read more.

The damage and fracture of coal is accompanied by a complex energy conversion process, and these different stages of energy evolution are closely related to coal failure. In this paper, an evolution model describing the behavior of coal failure was proposed using the energy dissipation under cyclic loading/unloading. The energy growth pattern and energy consumption characteristics of the coal fracture were analyzed under cyclic loading/unloading. An evolution model of the energy behavior of coal fracture was established. The damage variables of energy dissipation were defined, and a theoretical model was established. The parameters included the relationship between the energy state, damage state, and strength state according to the uniaxial cyclic loading/unloading test. The results show that there are energy excitation and inhibition effects in the process of coal fracture; that is, the accumulation rate and level of energy are affected by the energy storage state, and the energy storage rate changes in the mode of “low promotion and high inhibition”. The abrupt increase in dissipated energy can be regarded as the precursor of coal fracture. Based on the analysis of the characteristics of the damage and failure state and dissipated energy, the discriminant equation for the stability of the coal energy state was constructed; it is a meaningful discovery for predicting and evaluating coal failure. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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15 pages, 10256 KiB

Open AccessArticle

Analysis of the Dynamic Stability of Tailing Dams: An Experimental Study on the Dynamic Characteristics of Tailing Silt

by Fuqi Kang, Guangjin Wang, Yaoji Li, Binting Cai, Shujian Li, Lei Zhao and Xiaoshuang Li

Appl. Sci. 2023, 13(9), 5250; https://doi.org/10.3390/app13095250 - 22 Apr 2023

Cited by 1 | Viewed by 2032

Abstract

With the improvement in tailing mining-grade requirements and in mineral processing technology, tailing materials tend to be fine-grained. Under the action of earthquakes, a tailing dam is prone to liquefaction, which endangers the safety and stability of the dam. To further explore the [...] Read more.

With the improvement in tailing mining-grade requirements and in mineral processing technology, tailing materials tend to be fine-grained. Under the action of earthquakes, a tailing dam is prone to liquefaction, which endangers the safety and stability of the dam. To further explore the dynamic properties of tailing silt under cyclic stress, through a series of dynamic triaxial experiments, we investigated the growth of the hysteresis curve, the development of pore pressure, and the energy dissipation law of tailing silt. The experimental findings indicated that increasing the density of the sample significantly improves its liquefaction resistance and the pore pressure development curve can be fitted using the BiDoseResp function. At the same cyclic stress ratio, the sample’s anti-liquefaction strength did not rise monotonically with increasing confining pressure but changed variably at values near a specified low confining pressure; when the sample density rose under the same settings, the specific confining pressure reduced. We also further discussed the evolution law of the stress–strain curves of tailing silt. The results further explored the dynamic characteristics of tailing silt, which can provide some reference for the seismic design and reinforcement measures of many fine-grained tailing dams. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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14 pages, 3372 KiB

Open AccessArticle

Investigation of Microseismic Characteristics of Rock Burst Based on Fractal Theory

by Ping Wang, Ze Zhao, Da Zhang and Zeng Chen

Appl. Sci. 2023, 13(7), 4613; https://doi.org/10.3390/app13074613 - 5 Apr 2023

Cited by 3 | Viewed by 1442

Abstract

Microseismic monitoring is a common monitoring tool in the mining production process; for supervising a huge amount of microseismic data, effective analysis tools are necessary. In this study, the monitoring results of microseismic events at the Maoping lead-zinc mine in Yiliang County, Yunnan [...] Read more.

Microseismic monitoring is a common monitoring tool in the mining production process; for supervising a huge amount of microseismic data, effective analysis tools are necessary. In this study, the monitoring results of microseismic events at the Maoping lead-zinc mine in Yiliang County, Yunnan Province, and the spatiotemporal distribution characteristics of microseismic events are analyzed. We analyze the temporal characteristics of microseismic events using fractal theory, combining the change in fractal dimension with the rock burst incubation process. We also construct an observation area model for event anomalies based on the spatial distribution characteristics of microseismic events. The results show that the growth of the fractal dimension is consistent with the trend of the incubation process before rock burst, and the larger the fractal dimension, the higher the rock burst risk. The observation model, based on the density of microseismic events, can effectively refine the rock burst discrimination range and facilitate subsequent observations. An effective and feasible method of microseismic analysis is provided. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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19 pages, 6307 KiB

Open AccessArticle

Energy Behaviour of Coal Failure under Uniaxial Cyclic Loading/Unloading

by Chunlai Wang, Ze Zhao and Chang Zuo

Appl. Sci. 2023, 13(7), 4324; https://doi.org/10.3390/app13074324 - 29 Mar 2023

Cited by 3 | Viewed by 1332

Abstract

Coal failure is often the precursor of dynamic disaster. The energy evolution behaviour at different stress values was analysed under the gradation of equal amplitude cyclic loading/unloading. Based on the energy dissipation behaviour, the energy evolution model of the coal specimen was established. [...] Read more.

Coal failure is often the precursor of dynamic disaster. The energy evolution behaviour at different stress values was analysed under the gradation of equal amplitude cyclic loading/unloading. Based on the energy dissipation behaviour, the energy evolution model of the coal specimen was established. The multi-parameter energy behaviour predicting model was proposed. Then, the energy storage factor criterion, the energy tangent factor criterion, the energy dissipation growth factor criterion and the energy damage factor criterion of the coal specimen were proposed during the coal fracture process. The energy density and the energy storage status showed different evolution patterns under cyclic loading/unloading. The energy behaviours and status were different in fracture stages of coal specimens, and the dissipated energy behaviour had a sudden response during the failure process. The energy storage and energy dissipation mechanism were related to their respective limits. The energy storage mechanism showed a growth pattern of “low energy promotion, high energy suppression and dissipation promotion, cumulative suppression”. The damage evolution equation and the energy behaviour evolution criterion were established under the cyclic loading/unloading. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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16 pages, 6327 KiB

Open AccessArticle

Research on Multi-Scale Feature Extraction and Working Condition Classification Algorithm of Lead-Zinc Ore Flotation Foam

by Xiaoping Jiang, Huilin Zhao, Junwei Liu, Suliang Ma and Mingzhen Hu

Appl. Sci. 2023, 13(6), 4028; https://doi.org/10.3390/app13064028 - 22 Mar 2023

Cited by 1 | Viewed by 1646

Abstract

To address the problems of difficult online monitoring, low recognition efficiency and the subjectivity of work condition identification in mineral flotation processes, a foam flotation performance state recognition method is developed to improve the issues mentioned above. This method combines multi-dimensional CNN (convolutional [...] Read more.

To address the problems of difficult online monitoring, low recognition efficiency and the subjectivity of work condition identification in mineral flotation processes, a foam flotation performance state recognition method is developed to improve the issues mentioned above. This method combines multi-dimensional CNN (convolutional neural networks) characteristics and improved LBP (local binary patterns) characteristics. We have divided the foam flotation conditions into six categories. First, the multi-directional and multi-scale selectivity and anisotropy of nonsubsampled shearlet transform (NSST) are used to decompose the flotation foam images at multiple frequency scales, and a multi-channel CNN network is designed to extract static features from the images at different frequencies. Then, the flotation video image sequences are rotated and dynamic features are extracted by the LBP-TOP (local binary patterns from three orthogonal planes), and the CNN-extracted static picture features are fused with the LBP dynamic video features. Finally, classification decisions are made by a PSO-RVFLNs (particle swarm optimization-random vector functional link networks) algorithm to accurately identify the foam flotation performance states. Experimental results show that the detection accuracy of the new method is significantly improved by 4.97% and 6.55%, respectively, compared to the single CNN algorithm and the traditional LBP algorithm, respectively. The accuracy of flotation performance state classification was as high as 95.17%, and the method reduced manual intervention, thus improving production efficiency. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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11 pages, 1116 KiB

Open AccessArticle

Research of Peak Searching Technology for Separating Lithium from Coal Based on XRD Pattern

by Xiaoping Jiang, Yurong Liu and Tianning Xiu

Appl. Sci. 2023, 13(6), 4016; https://doi.org/10.3390/app13064016 - 22 Mar 2023

Viewed by 1311

Abstract

X-ray diffraction technology (XRD) is one of the common means of mineral separation, and peak identification and comparison is a key step. The symmetric zero-area conversion method (SZAC) performs well in peak searching of spectral lines, but its wide application is limited by [...] Read more.

X-ray diffraction technology (XRD) is one of the common means of mineral separation, and peak identification and comparison is a key step. The symmetric zero-area conversion method (SZAC) performs well in peak searching of spectral lines, but its wide application is limited by problems such as inaccurate identification results in specific scenes and dependence of parameter selection on spectral data. In this article, an improved symmetric zero-area conversion method (ISZAC) is proposed by combining the ideas of data fusion and passive anti-counterfeiting. The comparison method and flat peak screening were introduced, and the function group was designed to convert the spectral data after background deduction and intensity screening. The results were fused to obtain the peak address determination. Simulation and experimental results show that the improved method has higher accuracy and applicability. In addition, the method is easy to expand, and the conversion function group can be adjusted according to the spectral data characteristics to improve the recognition efficiency. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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12 pages, 8550 KiB

Open AccessArticle

Investigation of the Microseismic Response Characteristics of a Bottom Structure’s Ground Pressure Activity under the Influence of Faults

by Zeng Chen, Da Zhang, Chang Zuo, Ping Wang, Qiang Liu and Feng Shi

Appl. Sci. 2023, 13(6), 3796; https://doi.org/10.3390/app13063796 - 16 Mar 2023

Cited by 1 | Viewed by 1381

Abstract

To further understand the changing pattern of the bottom structure’s ground pressure activity under the influence of faults, predicting the potential occurrence of geological hazards and rock blast problems to reduce the loss of resources is important. A new microseismic monitoring system was [...] Read more.

To further understand the changing pattern of the bottom structure’s ground pressure activity under the influence of faults, predicting the potential occurrence of geological hazards and rock blast problems to reduce the loss of resources is important. A new microseismic monitoring system was established based on the original Pulang copper mine microseismic monitoring system. This paper analyzed the change law of the microseismic events on the fault in the first mining area of the Pulang copper mine, calculated the cumulative apparent volume and energy index changes of the microseismic events near the fault base, and quantitatively analyzed the microseismic event anomalies under the influence of the fault. The results show that rupture of the rock makes the cumulative apparent volume and energy index change significantly, while the timeliness of both makes the cumulative apparent volume predictive of the occurrence of rock fracture and rockburst, and the number of microseismic events corresponds to the intensity of the fault activation, which plays a predictive and guiding role in the subsequent study of fault activation, stability monitoring, and safe production in the mine area of Pulang copper mine. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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18 pages, 5006 KiB

Open AccessArticle

Classification of Mineral Foam Flotation Conditions Based on Multi-Modality Image Fusion

by Xiaoping Jiang, Huilin Zhao and Junwei Liu

Appl. Sci. 2023, 13(6), 3512; https://doi.org/10.3390/app13063512 - 9 Mar 2023

Cited by 3 | Viewed by 1528

Abstract

Accurate and rapid identification of mineral foam flotation states can increase mineral utilization and reduce the consumption of reagents. The traditional flotation process concentrates on extracting foam features from a single-modality foam image, and the accuracy is undesirable once problems such as insufficient [...] Read more.

Accurate and rapid identification of mineral foam flotation states can increase mineral utilization and reduce the consumption of reagents. The traditional flotation process concentrates on extracting foam features from a single-modality foam image, and the accuracy is undesirable once problems such as insufficient image clarity or poor foam boundaries are encountered. In this work, a classification method based on multi-modality image fusion and CNN-PCA-SVM is proposed for work condition recognition of visible and infrared gray foam images. Specifically, the visible and infrared gray images are fused in the non-subsampled shearlet transform (NSST) domain using the parameter adaptive pulse coupled neural network (PAPCNN) method and the image quality detection method for high and low frequencies, respectively. The convolution neural network (CNN) is used as a trainable feature extractor to process the fused foam images, the principal component analysis (PCA) reduces feature data, and the support vector machine (SVM) is used as a recognizer to classify the foam flotation condition. After experiments, this model can fuse the foam images and recognize the flotation condition classification with high accuracy. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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13 pages, 3195 KiB

Open AccessArticle

Experimental Study on Creep Characteristics of Unloaded Rock Masses for Excavation of Rock Slopes in Cold Areas

by Xingzhou Chen, Hai Jiang, Lili Chen, Wei Du and Sheng Gong

Appl. Sci. 2023, 13(5), 3138; https://doi.org/10.3390/app13053138 - 28 Feb 2023

Cited by 3 | Viewed by 1401

Abstract

Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank [...] Read more.

Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank slope under freeze–thaw action, triaxial unloading tests were carried out on sandstone, freeze–thaw tests simulating freezing strength were conducted, and triaxial creep tests were implemented with graded incremental loading on unloaded specimens subjected to freeze–thaw action. The test results showed that the total deformation of the unloaded specimens is significantly increased compared with the conventional specimens, and the lateral direction is more likely to produce creep behaviour than the axial direction. The level of confining pressure determines the level of creep deformation of unloaded specimens and affects the variation law of creep rate. The creep behaviour of the unloaded specimens is aggravated by freeze–thaw action and, the longer the freezing period, the larger the creep strain share, and the creep rate increases significantly. The creep damage pattern of the unloaded specimens subjected to freeze–thaw action is mainly manifested as shear damage, and the creep process intensifies the derivation of tension-type cracks in the specimens. The higher the confining pressure of the unloaded specimen, the more obvious the plastic characteristics and the weaker the brittle characteristics during creep failure. The freeze–thaw action significantly reduces the long-term strength of the unloaded specimen, which is approximately 50~55% of the instantaneous strength. The long-term strength decays significantly with an increasing freezing period, and the research results can provide a theoretical reference for the evaluation of the long-term stability of excavated and unloaded rock masses in cold areas. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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25 pages, 6215 KiB

Open AccessArticle

Automatic Identification System for Rock Microseismic Signals Based on Signal Eigenvalues

by Junzhi Chen, Hongbo Li, Chunfang Ren and Fan Hu

Appl. Sci. 2023, 13(4), 2619; https://doi.org/10.3390/app13042619 - 17 Feb 2023

Cited by 1 | Viewed by 1374

Abstract

The microseismic signals of rock fractures indicate that the rock mass in a particular area is changing slowly, and the microseismic signals of rock blasting indicate that the rock mass in a particular area is changing violently. It is of great significance to [...] Read more.

The microseismic signals of rock fractures indicate that the rock mass in a particular area is changing slowly, and the microseismic signals of rock blasting indicate that the rock mass in a particular area is changing violently. It is of great significance to accurately distinguish rock fracture signals and rock microseismic signals for analyzing the changes in the rock mass in the area where the signal occurs. Considering the microseismic signals of the Dahongshan Iron Mine, the time domain, frequency domain, energy characteristic distribution, and fractal features of each signal were analyzed after noise reduction of the original signal. The results demonstrate that the signal duration and maximum amplitude of the signal could not accurately distinguish the two types of signals. However, the main frequency of the rock fracture signal after noise reduction is distributed above 500 HZ, and the main frequency of the rock blasting signal is mainly distributed below 500 HZ. After the denoised signal is decomposed by the ensemble empirical simulation decomposition, the energy of the IMF1 frequency band of the rock fracture signal occupies an absolute dominant position, and the sum of the energy of the IMF2–IMF4 frequency bands of the rock blasting signal occupies a dominant position. The fractal box dimension of the rock fracture signal is mainly below 1.1, and the fractal box dimension of the rock blasting signal is mainly above 1.25. According to the above research results, an automatic signal recognition system based on the BP neural network is established, and the recognition accuracy of the rock blasting and rock fracture signals reached 93% and 94% respectively, when this system was used. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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13 pages, 5661 KiB

Open AccessArticle

Study on Paste Transformation and Parameter Optimization of Cemented Backfilling with Fine Tailings in Deep Gold Deposits

by Xinglin Wen, Zhengchen Ge, Yuemao Zhao, Zhenghua Zhang and Xianteng Sun

Appl. Sci. 2023, 13(3), 1850; https://doi.org/10.3390/app13031850 - 31 Jan 2023

Viewed by 1587

Abstract

The key to cementation backfilling in underground stopes of metal mines is quality and efficiency of backfilling. Backfilling quality is inseparable from the cementitious material as well as the tailings properties. To explore the influence of different factors on the strength of the [...] Read more.

The key to cementation backfilling in underground stopes of metal mines is quality and efficiency of backfilling. Backfilling quality is inseparable from the cementitious material as well as the tailings properties. To explore the influence of different factors on the strength of the backfilling body, the ratio of backfilling cementitious materials in the preparation process of backfilling slurry was experimentally studied to determine the economical and reasonable proportion of backfilling cementitious materials. Under the multi-factor test, it is concluded that the proportion concentration of 1:6 and 66% in the cemented specimen of medium and fine tailings meets the strength requirements of the surface layer of the backfilling body. Using the numerical simulation software FLAC^3D, the movement of rock mass under different backfillings is simulated, and the subsidence of overburden, the stress of the ore body, and the damage range of the plastic zone are analyzed. The results showed that, during the transition from full tailings cemented backfilling to medium-fine tailings paste backfilling, the vertical stress concentration area of the overlying strata shifts from the surrounding ore body to the backfilling body, the plastic zone decreases, and the complexity of failure forms gradually decreases. Finally, the transformation method from full tailings cementation backfilling to medium fine tailings paste backfilling is determined, and the medium fine tailings paste backfilling in a deep gold mine is realized. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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14 pages, 3776 KiB

Open AccessArticle

Spatial Characterization of Single-Cracked Space Based on Microcrack Distribution in Sandstone Failure

by Xiaolin Hou, Hongyu Zhai, Chunlai Wang, Tingting Wang, Xiang He, Xiang Sun, Zhian Bai, Baokun Zhou and Xiaoshuang Li

Appl. Sci. 2023, 13(3), 1462; https://doi.org/10.3390/app13031462 - 22 Jan 2023

Cited by 1 | Viewed by 1619

Abstract

To further understand the rock damage zone, an approach based on microcrack distribution was proposed to characterize the crack space of rock specimens in this research. Acoustic emission (AE) technology was utilized on sandstone to obtain the spatial distribution of microcracks in which [...] Read more.

To further understand the rock damage zone, an approach based on microcrack distribution was proposed to characterize the crack space of rock specimens in this research. Acoustic emission (AE) technology was utilized on sandstone to obtain the spatial distribution of microcracks in which uniaxial compression forms the single-cracked fracture. The proposed theoretical distribution pattern space (TDPS), 3D convex hull, and the minimum volume enclosing ellipsoid (MVEE) algorithms were adopted to analyze the geometric features of the crack space. It was found that the 3D convex hull method returned the smallest results in both area and volume of the crack space, and the largest results were provided by the proposed TDPS method. The difference between the results of the proposed TDPS method and the MVEE method became smaller after 85%. The deviation angle of the principal axis of the cracked space gradually decreased as the spatial scale decreased, while the other two major axes exhibited a tendency to increase at the 65% scale. The results indicate that a spatial scale from 65% to 85% is a reliable range for the characterization of crack space. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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13 pages, 1626 KiB

Open AccessArticle

Characteristics, Dynamic Analyses and Hazard Assessment of Debris Flows in Niumiangou Valley of Wenchuan County

by Zhiquan Yang, Xuguang Zhao, Mao Chen, Jie Zhang, Yi Yang, Wentao Chen, Xianfu Bai, Miaomiao Wang and Qi Wu

Appl. Sci. 2023, 13(2), 1161; https://doi.org/10.3390/app13021161 - 15 Jan 2023

Cited by 21 | Viewed by 2398

Abstract

Niumiangou valley, the epicenter of the 12 May 2008 Wenchuan earthquake (MS 8.0), became an area with frequent and dense debris flow disasters post-earthquake. Based on the in situ investigations after the earthquake on 14 August 2010 and a series of gathered data, [...] Read more.

Niumiangou valley, the epicenter of the 12 May 2008 Wenchuan earthquake (MS 8.0), became an area with frequent and dense debris flow disasters post-earthquake. Based on the in situ investigations after the earthquake on 14 August 2010 and a series of gathered data, characteristics and dynamic analyses of post-earthquake debris flows in Niumiangou valley were conducted, and then their hazard degree was assessed. Some research conclusions are obtained: (1) these post-earthquake debris flows have some typical characteristics, such as rainstorm viscous-type debris flow, happening usually between 11 p.m. and 5 a.m., broken out in the main channel as well as six branch gullies at the same time and also induced in the branches with good vegetation; (2) the dynamic parameters of Niumiangou debris flow (including volumetric weight, velocity, peak discharge, impact force, total amount of debris flow, total amount of solid materials washed out by single debris flow, maximum height of the debris flow rises and super elevation in bend) are relatively significant, and due to which it can be indicated that these debris flow disasters have great destructive power and harmfulness; (3) the hazard degree of debris flow in Niumiangou valley is very high, compared with the debris flows that occurred in the years of 2008 and 2013 in Niumiangou valley post-Wenchuan earthquake, and the comparison result shows that the hazard degree of debris flow in Niumiangou valley is relatively higher, which is consistent with the current situation. Therefore, according to these results, debris flows in Niumiangou valley are in the development phase and large-scale rainfall-induced debris flow disasters, with greater damage and stronger wallop, will easily occur in the rainy seasons of the 20 years after the earthquake. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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15 pages, 4695 KiB

Open AccessArticle

Mechanical Properties and Energy Evolution Law of Fractured Coal under Low Confining Pressure

by Zhiqi Wang, Xufei Gong and Xuebin Gu

Appl. Sci. 2022, 12(23), 12422; https://doi.org/10.3390/app122312422 - 5 Dec 2022

Cited by 5 | Viewed by 1587

Abstract

To study the mechanical properties and energy evolution characteristics of the shallow fractured coal in the Western China mining area, a series of triaxial compression tests was carried out on fractured coal specimens. The stress–strain curve, mechanical properties and failure characteristics were analyzed. [...] Read more.

To study the mechanical properties and energy evolution characteristics of the shallow fractured coal in the Western China mining area, a series of triaxial compression tests was carried out on fractured coal specimens. The stress–strain curve, mechanical properties and failure characteristics were analyzed. Then, the fractal characteristics and energy evolution law were investigated. Results show that with the increase of prefabricated crack number, the post-peak stage of the stress–strain curve changed from a linear drop to a stepped drop, indicating that the damage degree tends to moderate. Both the elastic modulus and peak strength decreased as the prefabricated crack number increased, whereas the peak strain did not exhibit a clear trend. The failure mode changed from overall tensile failure to tensile-shear mixed failure as the prefabricated crack number increased. With the increase of prefabricated crack number, the failure shape dimension increased linearly. The total energy and elastic energy decreased gradually with the increase of prefabricated crack number, whereas the dissipation energy increased gradually. The results can provide a better understanding of the failure mechanism of fractured coal and its application for control design. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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13 pages, 3059 KiB

Open AccessArticle

An Algorithm of Acoustic Emission Location for Complex Composite Structure

by Peixun Liu, Yanshuang Guo, Yanqun Zhuo, Wenbo Qi, Jiahui Feng, Hao Chen and Shunyun Chen

Appl. Sci. 2022, 12(23), 12323; https://doi.org/10.3390/app122312323 - 2 Dec 2022

Cited by 1 | Viewed by 1600

Abstract

Acoustic emission (AE) is widely used in engineering and rock mechanics. The algorithm of AE location based on homogeneous medium or single velocity structure is confronted with lower accuracy when it is applied to the actual working conditions that are prevailing complicated and [...] Read more.

Acoustic emission (AE) is widely used in engineering and rock mechanics. The algorithm of AE location based on homogeneous medium or single velocity structure is confronted with lower accuracy when it is applied to the actual working conditions that are prevailing complicated and heterogeneous. In this paper, an AE location algorithm based on complex composite structure (CCS) is proposed via carrying out the following studies: (1) A new travel time calculation scheme suitable for CCS with step-like velocity change is proposed based on an optimized shortest path algorithm. By doing this, a reasonable ray path that is only deflected at the interface is obtained to improve the travel time accuracy. The time complexity of the new algorithm is

O (n \log_{2} n)

. (2) The availability of the new algorithm is verified via a theoretical analysis under a one-dimensional velocity structure as well as an AE experiment using a complex structure under artificial excitation. (3) The AE location during the failure of a simulated CCS in the laboratory indicates that the new algorithm can effectively calculate the travel time and ray path of the sample. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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19 pages, 4923 KiB

Open AccessArticle

Mechanical Strength Decay Evaluation of Excavation Unloaded Rock Mass under Freeze-Thaw Conditions

by Xingzhou Chen, Wei Du, Lili Chen, Bin Ma, Sheng Gong, Hai Jiang and Wenrui Wang

Appl. Sci. 2022, 12(23), 12205; https://doi.org/10.3390/app122312205 - 29 Nov 2022

Cited by 2 | Viewed by 1572

Abstract

The quality of excavated and unloaded rock masses on steep and high slopes in cold regions is prone to deterioration, which in turn affects the long-term stability and safety of excavated slopes. Based on a triaxial unloading-damage test of sandstone, the unloading quantity [...] Read more.

The quality of excavated and unloaded rock masses on steep and high slopes in cold regions is prone to deterioration, which in turn affects the long-term stability and safety of excavated slopes. Based on a triaxial unloading-damage test of sandstone, the unloading quantity was used to analyze the evolution law of unloading damage; a freeze-thaw cycle test of the unloaded-damaged samples was carried out, and it was found that the average change in porosity and the reloading peak strength damage rate after freeze-thaw increased with the increase in the number of freeze-thaw cycles, and the porosity change characteristics were independent of the value of the confining pressure at the time of the unloading damage. An exponential decay model was used, and based on the average change in porosity after freeze-thaw, a freeze-thaw strength decay model that can take into account the effect of confining pressure was established, and its ability to predict the strength decay of unloaded-damaged rock samples after freeze-thaw was verified by experimental data. The research results provide a reference for the evaluation of freeze-thaw degradation of unloaded rock masses during slope excavation in cold regions. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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12 pages, 3156 KiB

Open AccessArticle

Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading

by Mingtao Gao, Hongyu Yan, Huiqiang Duan and Si Xiong

Appl. Sci. 2022, 12(22), 11810; https://doi.org/10.3390/app122211810 - 20 Nov 2022

Cited by 3 | Viewed by 1293

Abstract

The paper represents a test investigation of the mechanical properties and acoustic emission (AE) characteristics of low-strength coal specimens subjected to cyclic loading and unloading. From the lab tests, the following conclusions can be obtained: (1) The axial strain is very well linear [...] Read more.

The paper represents a test investigation of the mechanical properties and acoustic emission (AE) characteristics of low-strength coal specimens subjected to cyclic loading and unloading. From the lab tests, the following conclusions can be obtained: (1) The axial strain is very well linear with the loading–unloading cycle number, and the circumferential and volumetric strains are approximately quadratic functions with the loading–unloading cycle number; (2) Under the same loading stress interval, the elastic modulus firstly increases and then remains stable with the loading–unloading cycle number. In addition, the higher the maximum stress of a loading–unloading cycle, the more significant the plastic strengthening effect produced by this cycle; (3) The damage calculated by the cumulative AE hit count can better reflect the fact that the damage has been increasing in the loading phase and keeps basically unchanged in the unloading phase. So, the AE hit count, as a damage variable, can better describe the damage development of coal specimens. (4) The significant fluctuation of the AE b value can be used as the precursor of coal specimen failure. Additionally, the AE b value decreases rapidly at coal specimen failure. (5) The closer to the loading–unloading cycle of coal specimen failure, the more accurate the predicted “maximum magnitude” at coal specimen failure. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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14 pages, 3173 KiB

Open AccessArticle

Experimental Investigation of Task Performance and Human Vigilance in Different Noise Environments

by Chenyuan Yang, Liping Pang, Jin Liang, Xiaodong Cao, Yurong Fan and Jie Zhang

Appl. Sci. 2022, 12(22), 11376; https://doi.org/10.3390/app122211376 - 9 Nov 2022

Cited by 1 | Viewed by 1833

Abstract

Twelve healthy male college-age students were recruited to investigate the effects of different noise exposure conditions on complex task performance and vigilance. During each noise exposure, the Multi-Attribute Task Battery (MATB) with low, medium, and high mental workloads were conducted in the order [...] Read more.

Twelve healthy male college-age students were recruited to investigate the effects of different noise exposure conditions on complex task performance and vigilance. During each noise exposure, the Multi-Attribute Task Battery (MATB) with low, medium, and high mental workloads were conducted in the order designated by the Latin square method. Meanwhile, a psychomotor vigilance test (PVT) was used to evaluate human vigilance. Heart rate variability (HRV) signals were also collected while participants performed the tasks. The generalized additive mixed-effect model (GAMM) results showed that the increased mental workload had an inverted U-shaped effect on MATB task performance. Noise exposure had no significant impact on the overall performance of MATB tasks. However, when exposed to increased noise sharpness at low mental workloads, Tracking Task (TRA) performance significantly decreased, whereas the System Monitoring Task (SYS) performance was significantly improved. In addition, higher noise sound pressure level and sharpness would impair human vigilance, which was reflected in a lower mean sample entropy of HRV and worse performance on the PVT. The results indicated that noise control in the workplace should consider both sound pressure level and sharpness. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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13 pages, 1975 KiB

Open AccessReview

Analysis on the Spatial-Temporal Distribution Patterns of Major Mine Debris Flows in China

by Tianhao Ye, Guangjin Wang, Chunlai Wang, Hui Chen and Yingming Xin

Appl. Sci. 2023, 13(8), 4744; https://doi.org/10.3390/app13084744 - 10 Apr 2023

Cited by 1 | Viewed by 1565

Abstract

In order to provide more accurate data support for the prevention and control of geological disasters in mines, the article counts the major mine debris flow accidents in China from 1954 to 2019; studies the distribution of debris flow disasters in each province; [...] Read more.

In order to provide more accurate data support for the prevention and control of geological disasters in mines, the article counts the major mine debris flow accidents in China from 1954 to 2019; studies the distribution of debris flow disasters in each province; reveals the intra-annual and inter-annual variation patterns of the number of mine debris flow disasters; analyzes the distribution of mine debris flows under different geoenvironmental backgrounds; and combines AHP hierarchical analysis with a comprehensive regional evaluation of the likelihood of mine debris flows. The results of the study show that from 1954 to 2019, the number of major mine debris flow disasters first increased and then decreased. The proportion of mine debris flow disasters to the total number of debris flow disasters also showed a trend of first increasing and then decreasing, with the southwestern region being the area of high occurrence of mine debris flow, and the geoenvironmental areas of middle and low hills and middle and high mountains being the topographic areas of high occurrence of mine debris flow. More than 90% of the major mine debris flow disasters occurred from May to September, with the largest number of disasters occurring in July. A comprehensive evaluation of the regional nature of mine debris flow distribution based on the regional evaluation score is derived. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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19 pages, 4828 KiB

Open AccessProject Report

Research on Seismic Wave Quality Factor of Marble Jointed Rock Mass under SHPB Impact

by Changkun Sun, Changhong Li and Xiaoming Wei

Appl. Sci. 2022, 12(21), 10875; https://doi.org/10.3390/app122110875 - 26 Oct 2022

Cited by 6 | Viewed by 1636

Abstract

In order to quantitatively describe the energy dissipation law of jointed rock mass, we obtained the jointed cores in laboratory conditions using marble from the roof and floor of Jinchanghe Lead–zinc mine in Baoshan. The dissipative degree of stress wave in marble jointed [...] Read more.

In order to quantitatively describe the energy dissipation law of jointed rock mass, we obtained the jointed cores in laboratory conditions using marble from the roof and floor of Jinchanghe Lead–zinc mine in Baoshan. The dissipative degree of stress wave in marble jointed rock mass is measured by introducing quality factor

Q s

parameter. Based on the experimental principle of Split Hopkinson Pressure rod loading device (SHPB), we proposed a three-wave energy method of incident wave, reflected wave and projected wave for calculating jointed rock samples’ quality factor

Q s

based on stress wave energy. Using the SHPB test system for multiple specimens taken from the same piece of rock mass shock compression experiment, the three groups of specimens under different loading conditions gained incident wave and reflected wave and transmission wave experimental data, using the method of stress wave energy to deal with stress wave data, and calculate the joint sample maximum storage energy, dissipation energy and

Q s

quality factors. The results show that: ① The non-destructive breaking time–history strain of Dali rock mass under impact load is obtained by SHPB dynamic test system; combined with the deformation energy and dissipation energy calculation principle of quality factor, six groups of

Q s

experimental values are obtained. Although the

Q s

experimental values are discrete, the overall deviation is small with an average of 43.07. ② AUTODYN-Code was used to simulate the damage and fracture characteristics of rock mass with different quality factors under explosive dynamic load. The results showed that the radius of rock mass compression shear damage area gradually increased with the increase in porosity, but it was not obvious. Full article

(This article belongs to the Special Issue Research on Rock Mechanics and Backfilling Materials for Underground Mining)

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