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Failure Characteristics of Deep Rocks
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Failure Characteristics of Deep Rocks

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (25 November 2022) | Viewed by 60448

Special Issue Editors

Prof. Dr. Diyuan Li

E-Mail Website
Guest Editor
School of Resources and Safety Engineering, Central South University, Changsha 410083, China
Interests: rock mechanics; fracture mechanics; tunnelling engineering; mining engineering; rock fragmentation
Special Issues, Collections and Topics in MDPI journals
Dr. Zhenyu Han

E-Mail Website
Guest Editor
School of Resources and Safety Engineering, Central South University, Changsha 410017, China
Interests: rock dynamics; DEM simulation; fracture mechanics; induced seismicity
Special Issues, Collections and Topics in MDPI journals
Dr. Xin Cai

E-Mail Website
Guest Editor
School of Resources and Safety Engineering, Central South University, Changsha 410083, China
Interests: rock mechanics; rock dynamics; fracture; rock-water Interaction
Special Issues, Collections and Topics in MDPI journals
Dr. Shijie Xie

E-Mail Website
Guest Editor
School of Civil Engineering, Southeast University, Nanjing 210096, China
Interests: rock mechanics; fracture mechanics; constitutive model; direct shear
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The design and construction of underground engineering, such as mines, tunnels, hydropower stations and nuclear waste repositories, have been surging in scale and quantity over the past few decades, and it is believed that this trend will continue into the future. These large-scale engineering projects are closely related to rock materials and rock mechanics. When rock engineering enters increasingly deep exploitation, two critical scientific problems pose a serious threat to people's life and property: the construction efficiency of projects and the ecological environment. For one thing, geological disasters, including rockbursts, landslides and slabbing, frequently occur during the construction and operation of rock projects as geostress becomes higher. Scientists have managed to prevent the instability and breakage of surrounding rock. Additionally, researchers and workers hope to efficiently break hard rock in the excavation process. Therefore, the investigation and better understanding of the mechanical and fracture behaviors of deep rocks is of key importance in the scientific design and safe operation of deep rock engineering. This Special Issue is dedicated as a specific platform for all rock failure research. This topical section can serve as the missing link between applied and fundamental research journals. Therefore, “Failure Characteristics of Deep Rock” is dedicated to, and thus welcomes, all rock-based scientific research in order to deepen the understanding of deep rock hazards. Authors are therefore invited to submit their relevant research contributions to this Special Issue.

Prof. Dr. Diyuan Li
Dr. Zhenyu Han
Dr. Xin Cai
Dr. Shijie Xie
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • loading rate
  • fracture/damage mechanics
  • mechanical properties
  • observing methods
  • stress fields
  • constitutive relations
  • engineering applications
  • rock breaking methods
  • cracking process
  • numerical simulation

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Related Special Issue

Published Papers (27 papers)

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Research

14 pages, 5517 KiB  
Article
Comparative Analysis of Tunnel Plastic Zone Calculation and Engineering Measurement Based on Various Methods
by Zhihong Dong, Qingwen Yan, Qifeng Guo, Xun Xi, Xianquan Lei and Wenhui Tan
Minerals 2023, 13(2), 141; https://doi.org/10.3390/min13020141 - 18 Jan 2023
Cited by 1 | Viewed by 1567
Abstract
The characteristics of plastic zone are a critical basis for the control and stability analysis of the surrounding rock of roadways. This paper aims to investigate the rationality and applicability of the numerical methods for the plastic zone analysis of deep jointed rock [...] Read more.
The characteristics of plastic zone are a critical basis for the control and stability analysis of the surrounding rock of roadways. This paper aims to investigate the rationality and applicability of the numerical methods for the plastic zone analysis of deep jointed rock roadways. Based on the detailed investigation and experiments, The plastic zone distribution of roadway surrounding rock under different GSI values and different buried depths was analyzed by analytical methods, parameter reduction, and equivalent rock mass technology, and then the acoustic wave measurement method was used to carry out the field measurement and was compared with the simulation results. The results show that when GSI is large, the difference between the results is not obvious. When GSI is small, the results obtained by the parameter reduction method and the analytical method show a more drastic increase and the discreteness increases. The results obtained by the equivalent rock mass technique are generally close to the measured values, and the growth rate is more uniform. According to the convenience of the calculation parameters and the accuracy of the calculation, the suitable calculation methods for different working conditions were suggested. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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21 pages, 17996 KiB  
Article
A Multi-Scale Study on the Property Degradation of High-Temperature Treated Beishan Granite
by Xiang Zhang, Manke Wei, Zhen Lei and Ying Chen
Minerals 2023, 13(1), 27; https://doi.org/10.3390/min13010027 - 23 Dec 2022
Cited by 1 | Viewed by 1905
Abstract
Granite is the main host rock for the underground storage of nuclear waste in Beishan, China. Heat is continuously generated during the long-term disposal of nuclear waste; therefore, it is important to investigate the influence of high temperature on the physical and mechanical [...] Read more.
Granite is the main host rock for the underground storage of nuclear waste in Beishan, China. Heat is continuously generated during the long-term disposal of nuclear waste; therefore, it is important to investigate the influence of high temperature on the physical and mechanical properties and the constitutive relation of Beishan granite. In this study, laboratory experiments on heat-treated (25 ∘C, 200 ∘C, 400 ∘C, 600 ∘C and 800 ∘C) Beishan granite samples were performed in combination with nuclear magnetic resonance (NMR) analysis and regular physical-mechanical tests. The results show that the elastic modulus tends to decline faster at the temperature ranges of 25–200 ∘C and 600–800 ∘C by approximately 26.767% and 66.996%, respectively. Compared with the results at 25 ∘C, the peak stress decreases by 72.664% at 800 ∘C. The peak strain increases gradually from 25 ∘C to 600 ∘C and abruptly from 600 ∘C to 800 ∘C. The peak strain at 800 ∘C is 2.303× greater than that at 25 ∘C. Based on the damage theory, the Weibull distribution, the rock damage threshold point, and the residual strength, this study corrected the Drucker–Prager (D–P) criterion to consider the damage stress and then to establish the constitutive model of thermally damaged Beishan granite. The parameters required for the model are conventional mechanical parameters that can be calculated from the uniaxial test results, thus making the model convenient to apply. Meanwhile, the mechanical behavior of thermally damaged Beishan granite under uniaxial compression was simulated using the Particle Flow Code (PFC) to explore the development of cracks from the microscopic scale. The research results can provide theoretical support for the calculation and numerical simulation related to the mechanics of high-temperature treated rocks. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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15 pages, 2922 KiB  
Article
Application of a Hybrid Machine Learning Model for the Prediction of Compressive Strength and Elastic Modulus of Rocks
by Xiaoliang Jin, Rui Zhao and Yulin Ma
Minerals 2022, 12(12), 1506; https://doi.org/10.3390/min12121506 - 25 Nov 2022
Cited by 12 | Viewed by 1845
Abstract
This paper presents a machine learning-based approach to estimating the compressive strength and elastic modulus of rocks. A hybrid model, GWO-ELM, was built based on an extreme learning machine network optimized by the grey wolf algorithm. The proposed model was carried out on [...] Read more.
This paper presents a machine learning-based approach to estimating the compressive strength and elastic modulus of rocks. A hybrid model, GWO-ELM, was built based on an extreme learning machine network optimized by the grey wolf algorithm. The proposed model was carried out on 101 experimental datasets, and four commonly used models were used as benchmarks to evaluate the accuracy of the proposed model. The results showed that the proposed hybrid model can accurately achieve the prediction of elastic modulus and compressive strength with high correlation coefficients and small prediction errors. The prediction performance of the hybrid model is significantly better than the other four original models, and it is an alternative model for predicting the compressive strength and elastic modulus of rocks, which is recommended as an auxiliary tool for real-time prediction of rock mechanical properties. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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15 pages, 3899 KiB  
Article
A New Shear Constitutive Model Characterized by the Pre-Peak Nonlinear Stage
by Shijie Xie, Hang Lin, Zhenyu Han, Hongyu Duan, Yifan Chen and Diyuan Li
Minerals 2022, 12(11), 1429; https://doi.org/10.3390/min12111429 - 10 Nov 2022
Cited by 1 | Viewed by 1783
Abstract
The pre-peak shear stress-displacement curve is an important part of the study of the shear mechanical behavior of rock joints. Underpinned by the Haldane distribution, a new semi-analytical model for the pre-peak shear deformation of rock joints was established in this paper, the [...] Read more.
The pre-peak shear stress-displacement curve is an important part of the study of the shear mechanical behavior of rock joints. Underpinned by the Haldane distribution, a new semi-analytical model for the pre-peak shear deformation of rock joints was established in this paper, the validity of which was verified by laboratory and in situ experimental data. Other existing models were employed to make comparisons. The comparison results show that the model has superior adaptability and is more suitable for convex-type shear constitutive curves than existing models. Besides, only one parameter was introduced to the model, which is more convenient for application. All of these imply that the proposed model is an effective tool to evaluate the pre-peak shear constitutive curves of different rock joints. The research results can provide a reference for further understanding of the shear fracture characteristics of rock materials. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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15 pages, 5548 KiB  
Article
Fractal Dimension Analysis of Pores in Coal Reservoir and Their Impact on Petrophysical Properties: A Case Study in the Province of Guizhou, SW China
by Wei Fu, Wangshui Hu, Tongsheng Yi, Oumar Ibrahima Kane, Manting Zhang and Xin Huang
Minerals 2022, 12(11), 1425; https://doi.org/10.3390/min12111425 - 10 Nov 2022
Cited by 3 | Viewed by 1400
Abstract
Coal is a complex, porous medium with pore structures of various sizes. Therefore, it is difficult to accurately describe the characteristics of pore structure by using the traditional geometry method. The results from the present investigation suggest that the porous media system of [...] Read more.
Coal is a complex, porous medium with pore structures of various sizes. Therefore, it is difficult to accurately describe the characteristics of pore structure by using the traditional geometry method. The results from the present investigation suggest that the porous media system of the coal reservoir has obvious fractal characteristics at different scales. To study the complexity of the pores in the coal reservoir, 27 coal samples from Guizhou, SW China were studied. The fractal dimensions of coal pores were calculated, and the fractal dimension of a pore in a coal reservoir can be classified into two types: percolation and diffusion. The comprehensive fractal dimension can be obtained using the weighted summation method and the pore volume fraction of different fractal segments as the weight. The percolation fractal dimensions (Dp) of coal samples are between 2.88 and 3.12, the diffusion fractal dimensions (Dd) are between 3.57 and 3.84, and the comprehensive fractal dimensions (Dt) are between 3.05 and 3.63. The Dd values of all coal samples are all larger than the Dp values, which indicates that the random distribution and complexity of diffusion pores in coal are stronger than those of the percolation pores. The percolation fractal dimension decreases as the maturity degree increases, whereas the diffusion and comprehensive fractal dimensions increase. The diffusion pore volume fraction and total pore volume are all highly correlated with the comprehensive and diffusion fractal dimensions, respectively. The correlation between the comprehensive fractal dimension, diffusion pore volume fraction, and coal reservoir porosity is negative exponential, whereas the correlation between the total pore volume and coal reservoir porosity is positive linear. In comparison with the percolation and diffusion fractal dimensions, the comprehensive fractal dimension is better suited for characterizing the permeability of coal reservoirs. The fractal analysis of this paper is beneficial for understanding the relationship between the fractal characteristics of coal pores and properties. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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20 pages, 6158 KiB  
Article
Effects of Freeze–Thaw Cycling on Dynamic Compressive Strength and Energy Dissipation of Sandstone
by Bangbiao Wu, Ling Yang, Yong Mei, Yunhou Sun, Jinming Liu and Jun Shen
Minerals 2022, 12(10), 1331; https://doi.org/10.3390/min12101331 - 20 Oct 2022
Cited by 3 | Viewed by 1605
Abstract
In this study, the dynamic compressive strength and dissipated energy of rocks were investigated under hydrostatic pressure after different freeze–thaw cycles (FTCs). A split Hopkinson pressure bar (SHPB) with a lateral confining pressure chamber was used for the dynamic testing of sandstone specimens. [...] Read more.
In this study, the dynamic compressive strength and dissipated energy of rocks were investigated under hydrostatic pressure after different freeze–thaw cycles (FTCs). A split Hopkinson pressure bar (SHPB) with a lateral confining pressure chamber was used for the dynamic testing of sandstone specimens. The results indicated that under a certain loading rate and hydrostatic pressure, both the dissipative energy and dynamic compression strength of rocks decreased with the increase in the number of FTCs. The hydrostatic pressure significantly increased the dissipated energy and dynamic compression strength of rocks, and the enhancement became more pronounced as the number of FTCs increased. By analyzing the energy and damage characteristics of the specimens, after 40 FTCs, the internal damage of the specimens became critical and desensitized the dissipated energy to the loading rate. Based on the testing results, an empirical function was proposed to describe how the dissipated energy was related to the number of FTCs, hydrostatic pressure, and loading rate. It was demonstrated that the dissipated energy had a negative linear relation with FTC, which was enhanced by confinement. The dissipated energy of the specimen corresponded to the dynamic compression strength according to a quadratic function. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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22 pages, 17420 KiB  
Article
Failure Behavior of Cuboid Granite Sample with a Circular Hole beneath a Bonding Fracture under Biaxial Compression
by Diyuan Li, Jingtai Jiang and Feihong Gao
Minerals 2022, 12(10), 1328; https://doi.org/10.3390/min12101328 - 20 Oct 2022
Cited by 2 | Viewed by 1684
Abstract
Ore bodies incubating within fault zones are a common phenomenon in geological strata and pose a huge challenge for underground mining. To effectively exploit mineral resources, the layout of the mining roadway and the interaction between the roadway and geological fault must be [...] Read more.
Ore bodies incubating within fault zones are a common phenomenon in geological strata and pose a huge challenge for underground mining. To effectively exploit mineral resources, the layout of the mining roadway and the interaction between the roadway and geological fault must be considered. In this paper, a bonding fracture was formed on granite samples to simulate a closed fault, under which a circular hole was fabricated to simulate the roadway of the gold mine. We performed a biaxial compression test at a true-triaxial electrohydraulic servo testing system for granite samples with a combined fracture-hole structure. It is worth noting that the fracture inclination β and relative distance between fracture and hole L were taken into account. The digital image correlation (DIC) technique was used to observe the displacement and strain field evolution around the fracture-hole structure. Our results demonstrate that (1) the strength of the granite sample decreases with increasing bonding fracture dip angle β, and the displacement drops between the hanging wall and foot wall raised in both the horizontal and vertical displacement directions. Macroscopic cracks become dense, and the failure degree becomes severe around simulated fault areas. (2) With the increase in the distance L, the strength of the granite sample increases, the influence of the hole on the slip of the fracture plane is weakened, and the discontinuity of displacement becomes less obvious. (3) The maximum principal strain field quantitatively reveals the details of the crack initiation, propagation, and coalescence around the fracture-hole structure, and displacement nucleation is observed in the vertical displacement field. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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22 pages, 40037 KiB  
Article
Safe and Efficient Recovery Technique of Horizontal Isolated Pillar under Loose Tailings Backfill; A Case Study in a Zinc-Lead Mine
by Fan Feng, Jiqing Zhang, Zhikai Yan, Yedan Wu, Yamin Song, Zhiwei Xie and Xiang Cheng
Minerals 2022, 12(9), 1066; https://doi.org/10.3390/min12091066 - 24 Aug 2022
Cited by 3 | Viewed by 2005
Abstract
The presence of loose medium backfill above the horizontal pillar will technically hinder the efficient recovery of the pillar since the improper design and preserved roof protection layer height will potentially lead to casualties and equipment damage caused by large area collapse of [...] Read more.
The presence of loose medium backfill above the horizontal pillar will technically hinder the efficient recovery of the pillar since the improper design and preserved roof protection layer height will potentially lead to casualties and equipment damage caused by large area collapse of filled tailings as well as roof fall accidents. In this study, a safe and efficient technique for the recovery of isolated pillars under loose tailings backfill was carried out via field investigation, theoretical analysis, numerical simulation, and analytic hierarchy process using the isolated pillars in the 855 middle sublevel of Hongling Zinc-Lead Mine, Chifeng, Inner Mongolia, as a practical engineering background. Current studies have revealed that the optimal scheme for an isolated horizontal pillar recovered via the cut-and-fill stoping of a drift vertical to ore body strike involves preserving a 1.0-m roof protection layer above the crown pillar combined with a spaced mining extraction sequence. This design minimizes ore dilution and losses during the pillar extraction process under safe operation. Our research results provide theoretical and technical support for the safe and efficient recovery of isolated pillars under loose tailings backfill in similar mines. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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18 pages, 5934 KiB  
Article
Experimental Study on the Mechanical and Acoustic Emission Characteristics of Tuff with Different Moisture Contents
by Wenlong Dong, Lijun Han, Lingdong Meng, Hexuan Zhu, Shuai Yan, Changyu Xu and Yaning Dong
Minerals 2022, 12(8), 1050; https://doi.org/10.3390/min12081050 - 20 Aug 2022
Cited by 4 | Viewed by 1819
Abstract
Rock materials are often affected by water in underground engineering. In this study, the mechanical and failure characteristics of tuff under different moisture content were studied using laboratory tests. The moisture content variation of tuff was studied in water absorption tests, and the [...] Read more.
Rock materials are often affected by water in underground engineering. In this study, the mechanical and failure characteristics of tuff under different moisture content were studied using laboratory tests. The moisture content variation of tuff was studied in water absorption tests, and the mechanical and failure characteristics of tuff under different moisture contents were studied through uniaxial compression tests with a Micro-II acoustic emission (AE) control acquisition system. The results showed that the moisture content of tuff increases rapidly at the initial stage of water absorption tests and stabilizes after 180 h of immersion. According to the results of uniaxial compression tests, both uniaxial compressive strength and elasticity modulus decreased with the increase in moisture content. The AE parameters analyses showed that, when the moisture content increased, the accumulated AE counts and energy gradually decreased, and the “quiet period” at the initial stage of uniaxial compression tests lasted longer, and the RA (rise time⁄amplitude)–AF (AE counts⁄duration) distribution and the failure characteristics verified that the failure patterns evolved from shear failure to tensile failure. Scanning electron microscopy was used to observe the morphology of the fracture surface and analyze the influence of moisture content on the fracture characteristics of the tuff at the mesoscopic level. The results of this research can be used as a basis for studying the influence of water on tuff. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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17 pages, 14654 KiB  
Article
Full-Field Deformation and Crack Development Evolution of Red Sandstone under Impact and Chemical Erosion
by Junce Xu, Hai Pu and Ziheng Sha
Minerals 2022, 12(8), 1038; https://doi.org/10.3390/min12081038 - 18 Aug 2022
Cited by 5 | Viewed by 1862
Abstract
Coal mine reuse involves complex environments such as chemical erosion and dynamic perturbation. Therefore, the effect of chemical erosion on the dynamic behavior of the red sandstone was studied by split Hopkinson pressure bar (SHPB) tests under the strain rates of 70~125 s [...] Read more.
Coal mine reuse involves complex environments such as chemical erosion and dynamic perturbation. Therefore, the effect of chemical erosion on the dynamic behavior of the red sandstone was studied by split Hopkinson pressure bar (SHPB) tests under the strain rates of 70~125 s−1. The full-field deformation of the sample was then recorded through high-speed 3D digital image correlation (3D-DIC) technique. The dynamic deformation characteristics, especially the lateral strain, were extracted by averaging the lateral strain field by pixels. Also, the fracture behavior was investigated based on the evolution of strain localization in the strain field. The results indicated that the deformation field evolution of the sample is controlled by the chemical erosion effect and the loading strain rate. The chemical erosion lowers the stress threshold for strain localization and accelerates its expansion rate, which is closely related to the dynamic strength degradation of the sample. In contrast, the loading strain rate increases the dynamic strength but advances the occurrence of strain localization and shortens the time to the peak stress. The normalized stress thresholds for the initiation and development of cracks inside the sample under dynamic loading are reduced by chemical erosion, with the two thresholds dropping to 10%~30% and 20%~70% of the peak stress, respectively. The minimum thresholds for the initiation and development of cracks inside the red sandstone under dynamic loading are 11% and 24% of the peak stress, respectively. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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26 pages, 19853 KiB  
Article
Investigation of the Deformation Failure Occurring When Extracting Minerals via Underground Mining: A Case Study
by Xuanting Liu, Congxin Chen, Xiumin Liu, Kaizong Xia and Tianlong Wang
Minerals 2022, 12(8), 1025; https://doi.org/10.3390/min12081025 - 15 Aug 2022
Cited by 2 | Viewed by 1722
Abstract
Metal mines mined using the sublevel caving method often exhibit various environmental problems on the ground surface. This can affect the safety of the production process in the mining area. A numerical model using Universal Distinct Element Code has been established to investigate [...] Read more.
Metal mines mined using the sublevel caving method often exhibit various environmental problems on the ground surface. This can affect the safety of the production process in the mining area. A numerical model using Universal Distinct Element Code has been established to investigate deformation failure giving rise to this underground mining. The calculations are combined with in-situ monitoring data collected over a period of 10 years. The results indicate that the strata movement in the footwall can be divided into two stages: an arch caving development stage and post arch caving development stage. Mining disturbance is the main cause of caving in the arch caving development stage. The overlying strata experience ‘caving–stability–caving’, leading to the formation of an ‘arch-shaped’ caving pattern. In the post arch caving development stage, flexural-toppling deformation occurs in the strata in the direction of the collapse pit due to the tectonic stress present and high dip angles of the discontinuities. Through-going failure surface has been analyzed by studying the plastic state and displacement of elements. The formation of through-going failure surface is related to the flexural-toppling deformation and stress concentration caused by mining activities. Based on the different failure mechanisms, an efficient partition has been proposed such that the footwall can be divided into a stable zone, flexural-toppling failure zone, compression and slipping-toppling failure zone, and shear-slipping failure zone. The results are a useful reference when applied to the Chengchao Iron Mine and other similar metal mines. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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14 pages, 4946 KiB  
Article
Integrated Collaborative Control of “Shielding-Filling-Grouting” of 1 km Deep Large-Section Roadways: A Case Study
by Wei Zhang, Yandong Zhang, Yanchao Zhu, Jiajia Tang, Longtao Cheng and Zhiliang Suo
Minerals 2022, 12(7), 854; https://doi.org/10.3390/min12070854 - 4 Jul 2022
Cited by 1 | Viewed by 1615
Abstract
Effective control of deformation failure of surrounding rock in deep roadway has become an important prerequisite for the safe and efficient development of deep coal resources. In this study, the field measurement of the study area’s in-situ stress was carried out for the [...] Read more.
Effective control of deformation failure of surrounding rock in deep roadway has become an important prerequisite for the safe and efficient development of deep coal resources. In this study, the field measurement of the study area’s in-situ stress was carried out for the specific engineering geological conditions of the KCM −967 m level west-wing main track roadway. The west-wing main track roadway’s full-section deformation failure features were summarized and analyzed, and the main roadway’s surrounding rock nonlinear deformation failure mechanism was revealed from the perspective of elastoplastic mechanics. Based on that, a set of highly targeted integrated collaborative control technology of “shielding-filling-grouting” system was proposed. The industrial field test revealed that, after the above integrated collaborative control scheme was adopted, there was no strong deformation failure on the surface of the main roadway surrounding rock and deep rock mass, which played the role of active and passive support collaborative control, reduced the subsequent repeated repair and maintenance workload of the roadway, and satisfied the needs of long-term safe and efficient production of the mine. The results obtained provide a reference for the control of surrounding rock of deep and large-section roadways in other mining areas. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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17 pages, 5392 KiB  
Article
Experimental Test and Field Observations of an Electric Potential Monitoring Device for Dynamic Hazards during Mining Activities
by Yue Niu, Enyuan Wang, Zhonghui Li, Tiancheng Shan, Mingfu Wang, Jiali Wang, Honghao Wang, Hongchang Liu, Junhai Ding, Jingkun Wang, Feiyang Luo and Wei Shi
Minerals 2022, 12(7), 852; https://doi.org/10.3390/min12070852 - 3 Jul 2022
Cited by 3 | Viewed by 1789
Abstract
The EP (electric potential) signals can be generated during the deformation and fracture process of coal and rock mass. Meanwhile, the EP response is closely related to its stress state and damage evolution, which is expected to be used in monitoring and coal [...] Read more.
The EP (electric potential) signals can be generated during the deformation and fracture process of coal and rock mass. Meanwhile, the EP response is closely related to its stress state and damage evolution, which is expected to be used in monitoring and coal and rock dynamic disaster hazards. Based on this, this paper developed an EP monitoring device for mining to continuously monitor the temporal response characteristics and spatial distribution of coal seam internal EP signals in real time. Further, the experimental tests were carried out, whose results showed that the device has high monitoring sensitivity and little error for the EP signals and can reveal the loading state and damage degree of the coal and rock specimens during the deformation and fracture process. Moreover, the tests and application of EP monitoring were carried out during mining activities in the field. The results showed that the EP signals fluctuate during the coal mining stage and remain relatively stable during the maintenance stage. When the abnormal mining stress or the coal cannon phenomenon occurs, the intensity of EP signals increases rapidly and fluctuates violently, which has precursory response information for the hazards of dynamic disasters. Considering the advantages of sensitive response and nearly non-destructive monitoring, the study results can provide key monitoring equipment and research basis for field testing the EP signals during the mining process, to monitor and forecast the hazards of coal and rock dynamic disasters. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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24 pages, 46359 KiB  
Article
Effects of Accumulated Damage on the Dynamic Properties of Coal Measures Sandstone
by Ziheng Sha, Hai Pu, Junce Xu, Hongyang Ni and Shiru Guo
Minerals 2022, 12(7), 810; https://doi.org/10.3390/min12070810 - 25 Jun 2022
Cited by 6 | Viewed by 1992
Abstract
The coupling effect of accumulated damage and impact load substantially affects the integrity of the surrounding rock structure in deep coal mining engineering, which has inhibited safe and effective coal mining. Therefore, dynamic compression tests were performed on coal measures sandstone specimens with [...] Read more.
The coupling effect of accumulated damage and impact load substantially affects the integrity of the surrounding rock structure in deep coal mining engineering, which has inhibited safe and effective coal mining. Therefore, dynamic compression tests were performed on coal measures sandstone specimens with accumulated damage using the SHPB device. The effects of a high strain rate and accumulated damage on the sandstone’s mechanical behavior and damage evolution were investigated. The results reveal that accumulated damage has a considerable impact on specimen stress–strain curves and lowers dynamic compressive strength and deformation modulus substantially. The sandstone failure mode looks to be shear failure from a macroscopic perspective, while it appears to be intergranular fracture between the mineral particles from a microscopic perspective. The macroscopic and microscopic failure mechanisms of the sandstone specimens likewise conformed to the energy absorption law. The accumulated damage factor and the accumulated damage correction coefficient were presented in order to construct a statistical damage constitutive model of rocks based on the Weibull distribution. This model provides a decent description of the effects of accumulated damage and the strain rate on sandstone’s mechanical behavior, with parameters that are all of evident physical significance. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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13 pages, 2848 KiB  
Article
Assessment of Machine Learning Models for the Prediction of Rate-Dependent Compressive Strength of Rocks
by Ziquan Yang, Yanqi Wu, Yisong Zhou, Hui Tang and Shanchun Fu
Minerals 2022, 12(6), 731; https://doi.org/10.3390/min12060731 - 8 Jun 2022
Cited by 17 | Viewed by 2222
Abstract
The prediction of rate-dependent compressive strength of rocks in dynamic compression experiments is still a notable challenge. Four machine learning models were introduced and employed on a dataset of 164 experiments to achieve an accurate prediction of the rate-dependent compressive strength of rocks. [...] Read more.
The prediction of rate-dependent compressive strength of rocks in dynamic compression experiments is still a notable challenge. Four machine learning models were introduced and employed on a dataset of 164 experiments to achieve an accurate prediction of the rate-dependent compressive strength of rocks. Then, the relative importance of the seven input features was analyzed. The results showed that compared with the extreme learning machine (ELM), random forest (RF), and the original support vector regression (SVR) models, the correlation coefficient R2 of prediction results with the hybrid model that combines the particle swarm optimization (PSO) algorithm and SVR was highest in both the training set and the test set, both exceeding 0.98. The PSO-SVR model obtained a higher prediction accuracy and a smaller prediction error than the other three models in terms of evaluation metrics, which showed the possibility of the model as a rate-dependent compressive strength prediction tool. Additionally, besides the static compressive strength, the stress rate is the most important influence factor on the rate-dependent compressive strength of the rock among the listed input parameters. Moreover, the strain rate has a positive effect on the rock strength. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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15 pages, 5168 KiB  
Article
Study on the Stress Variation Law of Inclined Surrounding Rock Roadway under the Influence of Mining
by Qian Jia, Hai Wu, Tao Ling, Kai Liu, Weiwei Peng, Xu Gao and Yanlin Zhao
Minerals 2022, 12(5), 499; https://doi.org/10.3390/min12050499 - 19 Apr 2022
Cited by 3 | Viewed by 1869
Abstract
This study takes three roadways with similar burial depths in different strata in Xieqiao Mine of Huainan as its research object. This study involves the observation and analysis of borehole stress gauge data under the influence of mining pressure. The observation data show [...] Read more.
This study takes three roadways with similar burial depths in different strata in Xieqiao Mine of Huainan as its research object. This study involves the observation and analysis of borehole stress gauge data under the influence of mining pressure. The observation data show that: (1) under the influence of mining, the high-wall vertical stress increases as the distance from the roadway surface increases, and the peak point is at 6 m. The increment value of vertical stress at the low side has a maximum value at 8 m and a peak value at 14 m. The increase value of horizontal stress of the high side has two peaks, which are 4 m and 6 m, respectively. The increment of horizontal stress in low walls is also about 8 m. (2) The mining influence range of working face mining is about 150 m. Mining influence distance can be divided into three stages: 0–25 m, 25–60 m, and beyond 60 m. The increase of vertical and horizontal stress caused by mining increases sharply within 25 m from the working face. (3) The buried depth of the roadway has an influence on the range of mining influence and the increase of mining stress caused by working face mining. The more the buried depth of the roadway increases, the greater the range of mining influence and the increased value of mining stress. (4) After roadway excavation, the surface deformation of roadway surrounding rock reduces the increase of mining stress near the roadway surface. The mutual verification between the analysis results and theoretical calculation results is helpful to roadway support design and advanced support design of the working face. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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18 pages, 14475 KiB  
Article
Strain Energy Release and Deep Rock Failure Due to Excavation in Pre-Stressed Rock
by Peng Xiao, Diyuan Li and Quanqi Zhu
Minerals 2022, 12(4), 488; https://doi.org/10.3390/min12040488 - 16 Apr 2022
Cited by 4 | Viewed by 2562
Abstract
Deep rock engineering is in a high pre-stressed state before excavation. In this research, a method to calculate the release of strain energy caused by excavation in pre-stressed rock is proposed. The normal stress release after excavation leads to a reduction in strain [...] Read more.
Deep rock engineering is in a high pre-stressed state before excavation. In this research, a method to calculate the release of strain energy caused by excavation in pre-stressed rock is proposed. The normal stress release after excavation leads to a reduction in strain energy in rock specimens. The influence of excavation height and width on strain energy release is inconsistent under vertical loading. When the height of the hole is 1 mm, the strain energy release is large, and the increase in height of hole leads to a slow increase in the strain energy release. When the width of the hole is 1 mm, the strain energy release is very small, and the increase in the width of the hole leads to an increasingly faster release of strain energy. This strain energy release exponentially increases with the increase in the lateral pressure coefficient, showing a trend in the second power of the lateral pressure coefficient. Moreover, the tunnel failure caused by excavation under high stress is obtained by a numerical calculation. The failure modes of the deep tunnel model are strain rockbursts caused by tangential stress concentrations and spalling caused by normal stress release, which is also observed in the failure mode of the actual tunnel. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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20 pages, 5822 KiB  
Article
Research on the Mechanical Properties and Damage Constitutive Model of Multi-Shape Fractured Sandstone under Hydro-Mechanical Coupling
by Ying Zhang, Xu Wu, Qifeng Guo, Zhaohong Zhang, Meifeng Cai and Limei Tian
Minerals 2022, 12(4), 436; https://doi.org/10.3390/min12040436 - 31 Mar 2022
Cited by 6 | Viewed by 2133
Abstract
In this paper, mechanical property tests of sandstone with multiple shapes of prefabricated fractures (single, T-shaped, and Y-shaped fractures) are carried out through the MTS815 rock mechanics testing machine and the Teledyne ISCO D-Series Pumps system. Considering the hydro-mechanical coupling effects, the experiments [...] Read more.
In this paper, mechanical property tests of sandstone with multiple shapes of prefabricated fractures (single, T-shaped, and Y-shaped fractures) are carried out through the MTS815 rock mechanics testing machine and the Teledyne ISCO D-Series Pumps system. Considering the hydro-mechanical coupling effects, the experiments reveal the key thresholds, strength characteristics and deformation laws of multi-shape fractured sandstones during the progressive failure process. According to the elastic-plastic theory, the continuous damage theory and the statistical damage theory, a new damage model is constructed, which fully reflects the coupled effects among water, micro flaws and macroscopic prefabricated fractures. The crack closure stress σcc, crack initiation stress σci and damage stress σcd of multi-shape fractured sandstone samples are determined by the proposed volumetric strain response method. In the range of 0–90°, the σcc and σci of the multi-shape fractured sandstone samples are different, as well as the angles when the σcd and peak strength (σc) reach their peak values. The stress ratios (the σcc/σc, σci/σc, and σcd/σc are collectively referred to as stress ratios) are hardly affected by the shape and inclination of the fractures inside the rock. According to strength analysis and deformation characteristics, the weakening effect of water has less of an influence on the strength than prefabricated fractures. The stress–strain curve obtained, based on the hydro-mechanical coupling test, is in good agreement with the theoretical curve generated by the damage constitutive model, verifying the rationality of the damage constitutive model. In addition, the fracture inclination only affects the numerical value of the total damage variable of multi-shape fractured sandstone samples, and has minor effects on its variation trend. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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23 pages, 47342 KiB  
Article
Experimental Study on the Characteristics and Formation Mechanism of Dynamic Filter Cake for Slurry Shield Tunneling
by Yang Bai, Binsong Jiang, Le Yang, Yunqiu Liu, He Zheng and Yapeng Li
Minerals 2022, 12(3), 331; https://doi.org/10.3390/min12030331 - 7 Mar 2022
Cited by 8 | Viewed by 3214
Abstract
The key to guaranteeing excavation face stability in slurry shield tunneling is the formation of an impermeable dynamic filter cake. At the same time, the effect of the cutter head and rotation speed should be taken into account. We studied the characteristics and [...] Read more.
The key to guaranteeing excavation face stability in slurry shield tunneling is the formation of an impermeable dynamic filter cake. At the same time, the effect of the cutter head and rotation speed should be taken into account. We studied the characteristics and formation mechanism of the dynamic filter cake using a newly developed experimental apparatus. The experiment results show that the hysteretic infiltration zone appeared in the curves of stepped loading filtration while the cutter head was rotating, and the volume of water filtration increased by 11.2% compared to when the cutter head stopped. The higher the rotation speed was, the lower the conversion rate of the effective stress was. Under the same rotation speed, the formation time of the 6-cutter arm was almost 5 s slower than that of the 5-cutter arm. As the cutter arms and the rotation speed increased, the stratum’s electrical conductivity increased and stabilized at a distance of 20 cm from the cutter head. The filter cake transited from ‘filter cake plus an infiltration zone’ to ‘an infiltration zone without a filter cake’ with the increase of the rotation speed. The thickness of the dynamic filter cake was smaller than that of the static filter cake, the thickness of 10 groups decreased significantly, and the average thickness decreased by 76.15% at 1.0 rpm. The mesoscopic formation process of the dynamic filter cake can be divided into six stages. This study revealed the slurry penetration mechanism and filter cake characteristics present under cyclic damage by the shield cutter head to the filter cake and soil and provided theoretical support on how to maintain the stability of the excavation face during slurry shield tunneling. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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13 pages, 1941 KiB  
Article
Creep Constitutive Model and Numerical Realization of Coal-Rock Combination Deteriorated by Immersion
by Xuebin Li, Xuesheng Liu, Yunliang Tan, Qing Ma, Baoyang Wu and Honglei Wang
Minerals 2022, 12(3), 292; https://doi.org/10.3390/min12030292 - 25 Feb 2022
Cited by 14 | Viewed by 2006
Abstract
Coal-rock combination refers to the coal and rock as a whole, and the failure of the whole structure of the combination is the main cause for the instability of the deep underground engineering. In deep underground engineering, the coal-rock combination is usually under [...] Read more.
Coal-rock combination refers to the coal and rock as a whole, and the failure of the whole structure of the combination is the main cause for the instability of the deep underground engineering. In deep underground engineering, the coal-rock combination is usually under certain hydrogeological conditions, and it is prone to seepage and rheological failure instability accidents due to the long-term action of water and stress. In this study, the creep constitutive model of coal-rock combination considering the influence of moisture content was established based on the Burgers creep model. According to the experimental results of triaxial creep of rock, the relationship between the moisture content and the parameter of the Burgers creep model was derived, and the correctness of the constitutive model in this study was verified. Then, through the C++ language, the core equation of the model was modified, and the numerical calculation of the model was realized by introducing the coal-rock combination creep model considering the influence of moisture content into FLAC3D numerical simulation software. Finally, the model was used to simulate and study the creep characteristics of coal-rock combination with different moisture contents under triaxial loading. The results showed that the stress environment and moisture content have significant effects on the creep characteristics of the coal-rock combination. Under the same stress state, with the increased of moisture content, the strain rate of the coal-rock combination exhibited a non-linear rapid increase in the constant-velocity creep stage, the limit creep deformation and the instantaneous elastic deformation increased, and the viscosity coefficient was significantly decreased. For example, when the axial stress was 5 MPa and the moisture content increased from 0% to 1.5%, the strain rate increased by 44.06%, the limit creep deformation increased by 20%, the instantaneous elastic deformation increased 10.53%, and the viscosity coefficient decreased by about 50%. When the moisture content is 0%, the axial stress increased from 5 to 14 MPa, and the limit creep deformation increased nearly four times. With the increase of moisture content, this value will further expand. The research conclusions can provide a certain reference basis for the long-term stability control of surrounding rock in underground engineering affected by the water. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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19 pages, 6842 KiB  
Article
Experimental and Analytical Investigation into the Synergistic Mechanism and Failure Characteristics of the Backfill-Red Sandstone Combination
by Wen Zhang, Chengyuan Yan, Guoyue Zhou, Jinping Guo, Yanyu Chen, Baohua Zhang and Saisai Wu
Minerals 2022, 12(2), 202; https://doi.org/10.3390/min12020202 - 4 Feb 2022
Cited by 6 | Viewed by 1794
Abstract
The stability of underground goaf in filling mining is dominated by the interaction mechanism of the backfill-surrounding rock combination. In order to investigate the interaction mechanism and failure characteristics of the backfill-surrounding rock combination, backfill-red sandstone combinations with three different cement–sand ratios were [...] Read more.
The stability of underground goaf in filling mining is dominated by the interaction mechanism of the backfill-surrounding rock combination. In order to investigate the interaction mechanism and failure characteristics of the backfill-surrounding rock combination, backfill-red sandstone combinations with three different cement–sand ratios were prepared for uniaxial compression tests. The deformation and failure characteristics of the specimens were analyzed. It was found that at the cement–sand ratio of 1:4, the backfill and red sandstone interacted with and restricted each other, and the through cracks appeared in the whole specimens, which indicated that the backfill and red sandstone can jointly resist external loads and play a role in common bearing. However, with the decrease of the cement–sand ratio, the stress mainly acts on the backfill, and the deformation observed in the backfill is large while there is no obvious rupture in the rock. Based on the failure characteristics and the stress–strain curves of the specimens, the damage constitutive relationship that can describe the failure process and deformation characteristics is proposed. Correlated with the experiment results, the damage constitutive equation is established in three stages including compaction pre-synergy stage, quasi-elastic synergy deformation stage and rupture deformation stage. The failure characteristics observed in each stage are analyzed. The research results are of great significance to accurately understanding the interaction between backfill and surrounding rock, which can be used to design and select the mixture ratio of the filling materials. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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16 pages, 22585 KiB  
Article
The Meso-Structural Characteristics of Crack Generation and Propagation during Rock Fracturing
by Yanbo Zhang, Guangyu Gao, Shaohong Yan, Xulong Yao, Xiangxin Liu, Peng Liang and Yuedong Xu
Minerals 2022, 12(1), 94; https://doi.org/10.3390/min12010094 - 14 Jan 2022
Cited by 2 | Viewed by 2212
Abstract
Meso-structure is an important factor affecting the characteristics of rock fracture. To determine the factors influencing the internal meso-structural characteristics upon the crack generation and extension, rock samples were tested under uniaxial cyclic loading and unloading and examined using computed tomography (CT) scanning. [...] Read more.
Meso-structure is an important factor affecting the characteristics of rock fracture. To determine the factors influencing the internal meso-structural characteristics upon the crack generation and extension, rock samples were tested under uniaxial cyclic loading and unloading and examined using computed tomography (CT) scanning. CT scanning was used to visualize and investigate the entire process of fracture source generation and its development in three dimensions, and finally the location information of the fracture source was determined. The mineral composition and structure along the fracture path inside the specimen were studied by using a polarizing microscope, and the evolution of fracture propagation around mineral particles was revealed based on its mineralogical characteristics. Results indicate that based on the fracture source around different rock meso-structure types, the initial fracture source can also be divided into different types, namely, the primary porosity type, the micro-crack type, and the mineral grain type. The strength characteristics of mineral grains can determine whether the crack extends around the gravel or through it. The hard grains at the crack-tip promote the transformation of tensile stress to shear stress, which lead to the change in the direction of crack extension and bifurcation. The spatial shape of the cracks after rock fracture is related to the initial distribution of minerals and is more complicated in areas where minerals are concentrated. The crack extension around gravel particles also generates a mode of failure, affecting large grains with gravel spalling from the matrix. The findings provide a study basis for identifying the potentially dangerous areas and provide early warning for the safety of underground engineering construction operations. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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20 pages, 47388 KiB  
Article
Research on the Method and Model for Calculating Impact Load in the Rockburst Tunnel
by Zhiwei Yan, Dagang Liu, Zhilong Wang, Daming Zhao and Hongtao Tian
Minerals 2022, 12(1), 13; https://doi.org/10.3390/min12010013 - 22 Dec 2021
Cited by 4 | Viewed by 2604
Abstract
Among several design methods of tunnel supporting structure, the load-structure method is widely used in different countries, but the determination of load is essential in this design method. The problem of rockburst is becoming more prominent as tunnel engineering enters the deep underground [...] Read more.
Among several design methods of tunnel supporting structure, the load-structure method is widely used in different countries, but the determination of load is essential in this design method. The problem of rockburst is becoming more prominent as tunnel engineering enters the deep underground space. However, the research on the impact load on the supporting structure is insufficient in relevant fields. Therefore, from the perspective of energy, this paper deduces the method and model for calculating the impact load of the rockburst tunnel acting on the supporting structure by using the method of structural mechanics first, after the location effect of impact load is determined under different section types and different section sizes. The results indicated that: dynamic load factor K is related to the stiffness EI and supporting size coefficient K0 of the supporting structure, also the difference of impact load in different sections is proved. Tunnel rockburst-prone location is related to lateral pressure coefficient, thus when λ = 1, the probability of rockburst in the whole circular tunnel is the same, while side wall and vault are prone to rockburst in single-track horseshoe tunnel, and the side wall is prone to rockburst in double-track horseshoe tunnel; furthermore when λ > 1, the vault and the inverted arch are prone to rockburst; additionally, when λ < 1, the rockburst is most likely to occur in the arch waist of the circular tunnel and the side walls and the arch waist of the horseshoe tunnel. Finally, the rockburst tunnel’s local load-structure calculation model and the calculation process based on the model are provided. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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11 pages, 1244 KiB  
Article
Optimal Support Solution for a Soft Rock Roadway Based on the Drucker–Prager Yield Criteria
by Minghui Ma, Qifeng Guo, Jiliang Pan, Chi Ma and Meifeng Cai
Minerals 2022, 12(1), 1; https://doi.org/10.3390/min12010001 - 21 Dec 2021
Cited by 5 | Viewed by 2616
Abstract
Through theoretical calculation, the stress and deformation of surrounding rock can be analyzed, providing guidance for the support design and optimization of soft rock roadways. In this paper, theoretical solutions for both the optimal support pressure and the allowable maximum displacement of surrounding [...] Read more.
Through theoretical calculation, the stress and deformation of surrounding rock can be analyzed, providing guidance for the support design and optimization of soft rock roadways. In this paper, theoretical solutions for both the optimal support pressure and the allowable maximum displacement of surrounding rock are derived from the Drucker–Prager (DP) yield criteria and the steady creep criterion expressed by the third invariant of deviator stress. The DP criterion with different parameters is compared and analyzed with an engineering example. Then, based on the calculation results the effects of long-term strength, cohesion, and internal friction angle of soft rock on the maximum plastic zone radius and allowable maximum displacement of roadway are discussed. The results show that the optimal support solution of soft rock roadways based on the DP criteria can not only reasonably reflect the intermediate principal stress but can also be used to compare and discuss the influence of different DP criteria on the calculation results. The higher the long-term strength of the rock surrounding a roadway is, the smaller the optimal support force is and the larger the allowable maximum displacement is. When the calculated long-term strength of soft rock can ensure that the deformation of the roadway does not exceed the allowable maximum displacement, the roadway can maintain long-term stability without support. With an increase in the cohesion or internal friction angle of soft rock, the radius of the plastic zone decreases gradually and the allowable maximum displacement is reduced by degrees. The use of grouting and other means to improve the strength of surrounding rock can effectively reduce the roadway deformation and save support costs. This new theoretical solution can consider different intermediate principal stress effects and different DP strength criteria, enabling the parameters to become easier to determine. It has a wider range of applications, and the calculation results better demonstrate the strength potential of the surrounding rock. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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19 pages, 9439 KiB  
Article
Experimental Study on the Short-Term Uniaxial Creep Characteristics of Sandstone-Coal Composite Samples
by Dawei Yin, Feng Wang, Jicheng Zhang, Faxin Li, Chun Zhu and Fan Feng
Minerals 2021, 11(12), 1398; https://doi.org/10.3390/min11121398 - 10 Dec 2021
Cited by 4 | Viewed by 2681
Abstract
In this investigation, the uniaxial short-term creep tests with multi-step loading were conducted on the sandstone-coal composite samples, and the characteristics of creep strength, creep deformation, acoustic emission (AE), and creep failure of composite samples were studied, respectively. The creep strength of the [...] Read more.
In this investigation, the uniaxial short-term creep tests with multi-step loading were conducted on the sandstone-coal composite samples, and the characteristics of creep strength, creep deformation, acoustic emission (AE), and creep failure of composite samples were studied, respectively. The creep strength of the composite sample decreased with the stress-level duration, which was mainly determined by the coal and influenced by the interactions with the sandstone. The creep deformation and damage of sandstone weakened the deformation and damage accumulation within the coal, resulting in the larger strength for the composite sample compared with the pure coal sample. The axial creep strain of composite sample generally increased with the stress-level or the stress-level duration under same conditions. The AE characteristics of composite sample were related to the creep strain rate, the stress level, the stress level duration, and the local failure or fracture during creep loading. The micro or macro failure and fracture within the composite sample caused the rise in the axial creep strains and the frequency and intensity of AE signals, especially the macro failure and fracture. The creep failures of composite samples mainly occurred within the coal with the splitting ejection failure accompanied by the local shear failure, and no obvious failures were found within the sandstone. The coal in the composite sample became more broken with the stress-level duration. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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19 pages, 5657 KiB  
Article
Physical Simulation Test on Surrounding Rock Deformation of Roof Rockburst in Continuous Tunneling Roadway
by Yaobin Shi, Yicheng Ye, Nanyan Hu, Yu Jiao and Xianhua Wang
Minerals 2021, 11(12), 1335; https://doi.org/10.3390/min11121335 - 29 Nov 2021
Cited by 3 | Viewed by 2009
Abstract
To study the occurrence process, as well as the temporal and spatial evolution laws, of rockburst disasters, the roof deformation of continuous heading roadways during rockburst was studied through a physical similarity simulation test with a high similarity ratio and low strength. The [...] Read more.
To study the occurrence process, as well as the temporal and spatial evolution laws, of rockburst disasters, the roof deformation of continuous heading roadways during rockburst was studied through a physical similarity simulation test with a high similarity ratio and low strength. The deformation and failure evolution law of the roadway roof in the process of rockburst were analyzed by using detection systems, including a strain acquisition system and a high-power digital micro-imaging system. The results show that the rockburst of the roadway roof can be divided into four stages: equilibrium, debris ejection, stable failure, and complete failure stage. According to the stress state of a I–II composite crack, the theoretical buckling failure strength of the surrounding rock is determined as 1.43 times the tensile strength. The flexural failure strength of a vanadium-bearing shale is 1.29–1.76 times its compressive strength. With continuous advancement in the mining time, the internal expansion energy of the roadway roof-surrounding rock in the equilibrium stage continuously accumulates. The fracture network continuously increases, developing to the stable failure stage, with bending deformation, accompanied by continuous particle ejection until the cumulative stress in the failure stage increases, and the tensile state of the rock surrounding the roof expands radially into deep rock. A microscopic damage study in similar material demonstrated that the deformation of the roadway roof is non-uniform and uncoordinated. In the four stages, the storage deformation of the rock surrounding the roadway roof changes from small accumulation to continuous deformation, to the left (or deep rock). Finally, the roadway roof-surrounding rock becomes completely tensioned. The research results presented in this study provide a reference for the prediction and control of rockburst in practical engineering. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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13 pages, 4607 KiB  
Article
A Study on the Dynamic Strength Deterioration Mechanism of Frozen Red Sandstone at Low Temperatures
by Yang Yang, Niannian Zhang and Jianguo Wang
Minerals 2021, 11(12), 1300; https://doi.org/10.3390/min11121300 - 23 Nov 2021
Cited by 13 | Viewed by 2239
Abstract
In this study, the dynamic mechanical properties of red sandstone at low temperatures were studied by performing SHPB dynamic impact tests. According to damage and energy theories, the influences of different low temperatures on the dynamic strength, damage variable, and energy dissipation of [...] Read more.
In this study, the dynamic mechanical properties of red sandstone at low temperatures were studied by performing SHPB dynamic impact tests. According to damage and energy theories, the influences of different low temperatures on the dynamic strength, damage variable, and energy dissipation of red sandstone were analyzed. Combined with a fracture morphology analysis, the deterioration mechanism of the dynamic mechanical strength of red sandstone was deduced at lower negative temperatures. The research results showed that lower negative temperatures (<−30 °C) caused “frostbite” in red sandstone, which resulted in a sharp reduction in the macroscopic, dynamic mechanical strength of rock under high strain. Transient engineering disasters can easily occur under such a dynamic disturbance. According to the fracture morphology analysis, low temperatures generated a large number of cracks at the interface between the components of red sandstone. The plastic deformation ability of the crack tip was poor, and stability loss and expansion under high strain rate were readily achieved, resulting in low-stress brittle failure. However, due to the complex mineral composition of the cementitious materials, they were more susceptible to low temperature. Therefore, under the double action of dynamic load and low temperatures, it was found that damage occurred in the cementitious materials first, and then fracture of the red sandstone as a whole resulted. Full article
(This article belongs to the Special Issue Failure Characteristics of Deep Rocks)
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