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3 pages, 166 KiB

Open AccessEditorial

Mechanical Properties of Rocks under Complex Stress Conditions: Investigations Using Experimental and Numerical Methods

by Xuewei Liu, Zhizhen Zhang, Xiaomeng Shi and Xiaoli Xu

Appl. Sci. 2023, 13(9), 5753; https://doi.org/10.3390/app13095753 - 6 May 2023

Viewed by 1325

Abstract

Rock engineering constructions are widely attested in energy mining, geothermal development, and underground energy storage projects [...] Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

Research

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14 pages, 5171 KiB

Open AccessArticle

Study on Stiffness Parameters of the Hardening Soil Model in Sandy Gravel Stratum

by Xiaomeng Shi, Jinglai Sun, Yi Qi, Xiangyang Zhu, Xueming Zhang, Ruisong Liang and Hongjiang Chen

Appl. Sci. 2023, 13(4), 2710; https://doi.org/10.3390/app13042710 - 20 Feb 2023

Cited by 2 | Viewed by 2981

Abstract

Sandy gravel stratum is very common in tunnels and underground engineering projects. The accurate determination of mechanical parameters is crucial for engineering design and construction. The Hardening Soil (HS) Model, which accounts for both shear hardening and compression hardening, has demonstrated advantages in [...] Read more.

Sandy gravel stratum is very common in tunnels and underground engineering projects. The accurate determination of mechanical parameters is crucial for engineering design and construction. The Hardening Soil (HS) Model, which accounts for both shear hardening and compression hardening, has demonstrated advantages in numerical simulations. This study conducts large-scale mechanical experiments, including triaxial drained shear tests, loading-unloading tests, and standard consolidation tests, on sandy gravel specimens. The results reveal that the ratio of the three stiffness parameters in the HS Model, namely Young’s modulus under triaxial loading (E₅₀), oedometric loading (E_oed), and unloading-reloading (E_ur) is 1:1:4.3. The validity of the established stiffness ratio relationship is verified through numerical simulations of a foundation pit project and comparison with field monitoring data, demonstrating a consistent agreement between the simulation results and actual monitoring values. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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14 pages, 3092 KiB

Open AccessArticle

Analysis of Crack-Characteristic Stress and Energy Characteristics of Sandstone under Triaxial Unloading Confining Pressure

by Yanwei Duan, Guohua Zhang and Tao Qin

Appl. Sci. 2023, 13(4), 2671; https://doi.org/10.3390/app13042671 - 19 Feb 2023

Cited by 4 | Viewed by 1213

Abstract

The deformation and failure of underground engineering are usually caused by unloading. In this work, triaxial unloading confining pressure tests are carried out to simulate the failure process of rock mass caused by unloading, analyze the crack-characteristic stress, and study the energy evolution [...] Read more.

The deformation and failure of underground engineering are usually caused by unloading. In this work, triaxial unloading confining pressure tests are carried out to simulate the failure process of rock mass caused by unloading, analyze the crack-characteristic stress, and study the energy evolution of rock under unloading and the pre-peak and post-peak energy characteristics combined with the energy theory. The results show that, when the confining pressure increases from 5 MPa to 20 MPa, crack closure stress σ_cc, crack initiation stress σ_ci, dilatancy stress σ_cd, and peak stress σ_p are 6.34 times, 2.75 times, 1.93 times, and 1.66 times higher than the original, respectively. By comparing the increase in crack-characteristic stress, it can be found that the confining pressure has a large effect on the crack closure stress and crack initiation stress, while the dilatation stress and peak stress have relatively little influence. From the perspective of energy evolution, the pre-peak axial absorption energy U₁ increases exponentially, the elastic energy U^e is similar to U₁, and the circumferential consumption energy U₃ and dissipation energy U^d are small. After reaching the peak stress, the growth rate of U₁ decreases slightly, U^e decreases rapidly, and U₃ increases rapidly but only as a small fraction of the total energy, while U^d grows almost exponentially and rapidly becomes the main part of the energy. Under each crack-characteristic stress state, the energy characteristic parameters gradually increase with the increase in confining pressure, which is manifested by the increase in slope in the linear fitting formula of energy characteristic parameters. The release process of the releasable elastic energy after the peak stress can be divided into three stages of “slow–fast–slow”, and the energy release process shows an obvious confining pressure effect. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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15 pages, 9891 KiB

Open AccessArticle

Influence of Stress Anisotropy on Petrophysical Parameters of Deep and Ultradeep Tight Sandstone

by Hui Zhang, Ke Xu, Binxin Zhang, Guoqing Yin, Haiying Wang, Zhimin Wang, Chao Li, Shujun Lai and Ziwei Qian

Appl. Sci. 2022, 12(22), 11543; https://doi.org/10.3390/app122211543 - 14 Nov 2022

Cited by 2 | Viewed by 1288

Abstract

Rock mechanics parameters control the distribution of in situ stress and natural fractures, which is the key to sweet spot evaluation in reservoir engineering. Combined with the distribution of in situ stress, an experimental scheme of stress on rock physical parameters was designed. [...] Read more.

Rock mechanics parameters control the distribution of in situ stress and natural fractures, which is the key to sweet spot evaluation in reservoir engineering. Combined with the distribution of in situ stress, an experimental scheme of stress on rock physical parameters was designed. The results show that rock sonic velocity is extremely sensitive to water saturation under overburden pressure. At ultrasonic frequencies, when the water saturation increases from 0% to 80%, the P-wave velocity increases first and then decreases. When the water saturation continues to increase to 100%, the P-wave velocity increases. This is due to the effect of water saturation on the shear modulus. Saturation is negatively correlated with shear wave velocity and resistivity. Different minerals have different control effects on the rock P-S wave velocity ratio. Quartz content plays a dominant role, and the two are negatively correlated, followed by feldspar and clay, and the two are positively correlated with the P-S wave ratio. The confining pressure, axial compression, stress ratio and burial depth are positively correlated with the P-S wave and negatively correlated with the P-S wave ratio; in descending order, the influencing factors of stress on the petrophysical parameters are maximum stress ratio > confining pressure > axial pressure. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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20 pages, 10604 KiB

Open AccessArticle

Prediction Method for Mine Earthquake in Time Sequence Based on Clustering Analysis

by Peng Zhang, Xiaolin Li and Junli Chen

Appl. Sci. 2022, 12(21), 11101; https://doi.org/10.3390/app122111101 - 2 Nov 2022

Cited by 6 | Viewed by 1540

Abstract

Under the background of the intelligent construction of a coal mine, how to efficiently extract effective information from the massive monitoring data of mine earthquakes, and improve prediction accuracy, is a research hotspot in the field of coal mine safety production. In view [...] Read more.

Under the background of the intelligent construction of a coal mine, how to efficiently extract effective information from the massive monitoring data of mine earthquakes, and improve prediction accuracy, is a research hotspot in the field of coal mine safety production. In view of this problem, more and more machine learning methods are being applied to the prediction on mine earthquakes. Considering that clustering analysis can enhance the correlation between microseism data, we propose a method whose main idea is to cluster microseism data before establishing the prediction model, and then train the model, so as to improve prediction accuracy. Specifically, microseism events on a working face are divided into clusters in advance by the Spatial Temporal-DBSCAN(ST-DBSCAN) algorithm, then a prediction model is established with Support Vector Regression (SVR) to predict the occurrence location and daily frequency of high-energy mine earthquake events. A set of engineering experiments were conducted in H Coal Mine, and the results show that the spatial-temporal clustering analysis of microseism events can indeed improve the prediction accuracy of machine learning methods on mine earthquakes. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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16 pages, 15809 KiB

Open AccessArticle

Motion Characteristics of Collapse Body during the Process of Expanding a Rescue Channel

by Yanlong Fu, Kai Xie, Fukun Xiao, Gang Liu, Zhiyuan Hou and Rui Zhang

Appl. Sci. 2022, 12(21), 11034; https://doi.org/10.3390/app122111034 - 31 Oct 2022

Cited by 1 | Viewed by 1152

Abstract

For the rapid construction of a rescue channel in the process of underground emergency rescue, a method for the expanded rescue channel in the collapse body is proposed and verified by a model test and a numerical simulation experiment. The motion characteristics and [...] Read more.

For the rapid construction of a rescue channel in the process of underground emergency rescue, a method for the expanded rescue channel in the collapse body is proposed and verified by a model test and a numerical simulation experiment. The motion characteristics and motion law of the expanded collapse body are analyzed on the basis of the mechanics of granular media, and a comparative simulation study on the main influencing factors of the collapse body motion is carried out. The results show that: (1) When the collapse body is expanded for a rescue channel, it will form three types of six relative slip planes. According to the position of the slip plane and the distribution of displacement, the collapse body can be divided into a direct displacement region, a stable region, and an indirect displacement region. (2) The expansion process can be divided into the initial start-up stage, the uplift stage, and the collapse stage, according to the formation time of the slip plane and the displacement law of the collapse body. (3) The results of the numerical simulation and the theoretical analysis of the granular media show that the dip angle of the slip plane is determined by the internal friction angle of the collapse particles, and the dip angles of the three slip planes are below

θ_{1} = 90 ° - φ

,

θ_{2} = 45 ° + φ / 2

, and

θ_{3} = 90 ° + φ / 2

. (4) The transverse scope and longitudinal distance is brought by the expansion increase with the increase in the expansion size, and the simulated dip angles of the slip plane are larger than the theoretical values due to the size effect. (5) In the expansion process, the strong force chain in the collapse body is concentrated in the stress arch above the expander device, and the failure and reconstruction laws of the stress arch at each stage are consistent with the formation of the slip plane and the uplift and instability law of the collapse body. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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17 pages, 10992 KiB

Open AccessArticle

Mechanism of Coal Burst Triggered by Disturbing Mining-Induced Stress: An Experimental Investigation

by Jinzheng Bai, Linming Dou, Xuwei Li, Jinrong Cao, Kangkang Wang, Yanjiang Chai and Jiliang Kan

Appl. Sci. 2022, 12(21), 10993; https://doi.org/10.3390/app122110993 - 30 Oct 2022

Cited by 1 | Viewed by 1576

Abstract

The true triaxial test can accurately simulate the dynamic and static load superposition environment of deep mining and then reproduce the spatial and temporal evolution process of coal-rock dynamic disasters. This study used a self-developed true triaxial coal-rock dynamic behavior test system to [...] Read more.

The true triaxial test can accurately simulate the dynamic and static load superposition environment of deep mining and then reproduce the spatial and temporal evolution process of coal-rock dynamic disasters. This study used a self-developed true triaxial coal-rock dynamic behavior test system to investigate the dynamic failure characteristics and mechanism of coal bursts under different mining-induced stress disturbances. The results show that the perturbation duration of the coal samples under quasi-static load decreases with the increase of the disturbance rate, and the perturbation stress level increases first and then decreases. The coal samples can accumulate higher strain energy and show progressive and dynamic failure. The perturbation duration and stress peak of the coal sample under the cycle load decreased with the increase of the cycle amplitude and frequency, and the coal sample first spalled off on the free surface. The damage then developed internally until the coal burst. The perturbation duration and stress peak of coal samples decrease with the increase of transient stress and the perturbation stress levels. The dynamic failure process of coal samples is straightforward, and the strength of coal burst is violent and is more difficult to predict. The conclusions obtained help to deepen the understanding of the triggering mechanism of coal bursts. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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17 pages, 6727 KiB

Open AccessArticle

Experimental Investigation on Compressive Strength, Ultrasonic Characteristic and Cracks Distribution of Granite Rock Irradiated by a Moving Laser Beam

by Lianfei Kuang, Lipeng Sun, Dongxu Yu, Yijiang Wang, Zhaoxiang Chu and Jo Darkwa

Appl. Sci. 2022, 12(20), 10681; https://doi.org/10.3390/app122010681 - 21 Oct 2022

Cited by 5 | Viewed by 3105

Abstract

Efficient fracturing is the key issue for the exploitation of geothermal energy in a Hot Dry Rock reservoir. By using the laser irradiation cracking method, this study investigates the changes in uniaxial compressive strength, ultrasonic characteristics and crack distributions of granite specimens by [...] Read more.

Efficient fracturing is the key issue for the exploitation of geothermal energy in a Hot Dry Rock reservoir. By using the laser irradiation cracking method, this study investigates the changes in uniaxial compressive strength, ultrasonic characteristics and crack distributions of granite specimens by applying a laser beam under various irradiation conditions, including different powers, diameters and moving speeds of the laser beam. The results indicate that the uniaxial compressive strength is considerably dependent on the power, diameter and moving speed of the laser beam. The ultrasonic-wave velocity and amplitude of the first wave both increase with a decreased laser power, increased diameter or moving speed of the laser beam. The wave form of irradiated graphite is flattened by laser irradiation comparing with that of the original specimen without laser irradiation. The crack angle and the ratio of the cracked area at both ends are also related to the irradiation parameters. The interior cracks are observed to be well-developed around the bottom of the grooving kerf generated by the laser beam. The results indicate that laser irradiation is a new economical and practical method that can efficiently fracture graphite. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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17 pages, 4901 KiB

Open AccessArticle

Mechanical Properties and Damage Evolution of Heated Granite Subjected to Liquid Nitrogen Cooling

by Chunbo Zhou, Feng Gao, Chengzheng Cai, Wenqi Zheng and Liupeng Huo

Appl. Sci. 2022, 12(20), 10615; https://doi.org/10.3390/app122010615 - 20 Oct 2022

Cited by 4 | Viewed by 1405

Abstract

To investigate the effect of liquid nitrogen on the granite failure process, the deterioration effect of liquid nitrogen on heated granite was investigated from experimental and theoretical perspectives. The mechanical properties of heated granite (25, 100, 200, 300, and 400 °C) after different [...] Read more.

To investigate the effect of liquid nitrogen on the granite failure process, the deterioration effect of liquid nitrogen on heated granite was investigated from experimental and theoretical perspectives. The mechanical properties of heated granite (25, 100, 200, 300, and 400 °C) after different cooling treatments (air cooling and liquid nitrogen cooling) were investigated by uniaxial compression tests. The damage evolution analysis was performed by a statistical damage constitutive model and the dissipation energy ratio was newly defined. The results show that there is an increase in the uniaxial compressive strength of heated granite before 200 °C, which is due to the competitive relationship between the thermal cracking and crack closure. Liquid nitrogen cooling can deteriorate the mechanical properties of heated granite in terms of strength and deformability. At 400 °C, the reduction rates of compressive strength and stiffness between air cooling and liquid nitrogen cooling reached 32.36% and 47.72%, respectively. Liquid nitrogen cooling induces greater initial thermal damage and, consequently, leads to a greater degree of total damage before the peak stress and makes rock easier to be damaged. At 400 °C, the total damage at the peak stress increased from 0.179 to 0.587 after the liquid nitrogen cooling. The difficulty of damage can be quantified by the dissipation energy ratio. In addition, the deterioration of liquid nitrogen on granite is positively related to temperature. This study confirmed the deterioration effect of liquid nitrogen and promoting effect of temperature, providing a theoretical approach to the degradation mechanism of liquid nitrogen. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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17 pages, 4587 KiB

Open AccessArticle

Research on Rock Strength Test Based on Electro-Hydraulic Servo Point Load Instrument

by Xiaoxia Zhou, Lei Qiao, Faquan Wu, Zhaoyuan Wang, Yinhong Chen and Jie Wu

Appl. Sci. 2022, 12(19), 9763; https://doi.org/10.3390/app12199763 - 28 Sep 2022

Cited by 6 | Viewed by 1430

Abstract

A new electro-hydraulic servo point load instrument was designed to address the problem that the existing point load instrument cannot be loaded continuously and uniformly; different loading rates (using three loading rates: 0.1, 0.5, 1.0 kN/s) were conducted on fine-crystalline granite, coarse-crystalline granite, [...] Read more.

A new electro-hydraulic servo point load instrument was designed to address the problem that the existing point load instrument cannot be loaded continuously and uniformly; different loading rates (using three loading rates: 0.1, 0.5, 1.0 kN/s) were conducted on fine-crystalline granite, coarse-crystalline granite, and siltstone (each rock sample contains four sizes: 20³, 30³, 40³, 50³ mm³) for point load tests. Firstly, the influence of loading rate on the axial stress distribution of rock sample loading was investigated in conjunction with the rock strength damage theory. Next, the influence of rock sample size and loading rate on different standard point load strength evaluation methods was analyzed to find a reasonable evaluation method and loading rate and range of rock sample size. Finally, the relationship between standard point load strength and uniaxial compressive strength was analyzed on this basis to obtain its empirical conversion formula. The results show that: (1) With the increase in the loading rate of point load, the tensile and compressive stresses in the loading axis increase, and the compressive stresses near the center of the loading axis of the rock sample are more influenced by the loading rate; the standard point load strength increases with the increase in the loading rate, but the increase in the standard point load strength decreases when the loading rate increases to a certain range. (2) With the increase in size, the standard point load strength solved by method I, method III, and method IV has an obvious size effect, while the size effect of standard point load strength solved by method II is not obvious. (3) The conversion factors of fine-crystalline granite, coarse-crystalline granite, and siltstone were obtained by zero-intercept linear regression analysis as 16.80, 15.32, and 14.60, respectively, which indicated that the conversion factors of rocks with high strength were higher than those of rocks with low strength. The present research results can provide theoretical support for revising the existing point load strength calculation equations. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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19 pages, 7461 KiB

Open AccessArticle

Effect of Freeze-Thaw Damage on the Physical, Mechanical, and Acoustic Behavior of Sandstone in Urumqi

by Junce Xu, Hai Pu and Ziheng Sha

Appl. Sci. 2022, 12(15), 7870; https://doi.org/10.3390/app12157870 - 5 Aug 2022

Cited by 6 | Viewed by 1439

Abstract

The Urumqi area in China is a seasonally cold region, and the rock structures in the region are susceptible to freeze-thaw (F-T) weathering. Therefore, this study investigated the effect of F-T on the physical, mechanical, and fracture behavior of sandstone from Urumqi. The [...] Read more.

The Urumqi area in China is a seasonally cold region, and the rock structures in the region are susceptible to freeze-thaw (F-T) weathering. Therefore, this study investigated the effect of F-T on the physical, mechanical, and fracture behavior of sandstone from Urumqi. The acoustic emission method (AE) was used to determine the stress thresholds for the initiation and development of cracks in the samples under cyclic F-T action. The results suggested that parameters such as P-wave velocity, elastic modulus, and peak stress presented a significant negative correlation with F-T damage, while porosity exhibited a close positive correlation. The elastic modulus of the sample was more sensitive to the F-T action with the smallest half-life (27 cycles) and the largest decay factor (0.0254). In addition, the stress threshold for micro-cracks development and macro-cracks initiation in the samples decreased with increasing F-T damage. After 30 F-T cycles, the stress threshold for micro-cracks propagation in the samples decreased from 20.73 MPa to 5.02 MPa by approximately 76%. The normalized stress threshold for the macro-cracks initiation was also decreased from 0.93 to 0.71. Moreover, the macro-cracks damage zone of the samples showed an increasing trend with F-T damage, from 7% under natural conditions to 29% after 30 cycles. It is concluded that F-T action lowers the stress thresholds for cracks development in sandstone in the Urumqi area, posing serious safety concerns for mass rock engineering in this area. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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13 pages, 3550 KiB

Open AccessArticle

Experimental Study on Mechanical Properties of High Temperature Granite with Different Cooling Methods

by Jin-Song Zhang, Yu Lu, Jian-Yong Pang and Yi-Shun Bu

Appl. Sci. 2022, 12(12), 5968; https://doi.org/10.3390/app12125968 - 11 Jun 2022

Cited by 7 | Viewed by 1643

Abstract

Due to various factors, high-temperature rocks are often affected by different cooling methods. They will lead to changes in rock mechanical properties, which firmly connect with the safety and stability of practical projects. At present, there are many studies of the microscopic characteristics [...] Read more.

Due to various factors, high-temperature rocks are often affected by different cooling methods. They will lead to changes in rock mechanical properties, which firmly connect with the safety and stability of practical projects. At present, there are many studies of the microscopic characteristics of rocks under different cooling methods, but few on the mechanical characteristics of rocks under the same conditions. Therefore, it is necessary to carry out experimental research on the mechanical properties of rock under different cooling methods. The study shows that the deterioration degree of the sample increases gradually with temperature rising and the cooling methods have different effects on the change of the sample in mass, volume and density. The stress–strain curve of the sample is divided into the crack compaction stage, elastic deformation stage, nonlinear deformation stage and failure stage. The peak strength of the naturally cooled sample is higher than that of the water cooled. The peak strength comes with a trend that goes up first, and then down with the temperature increasing. The uniaxial compression failure of the sample under uniaxial action is tensile failure. The failure characteristic of the sample is influenced both by the cooling modes and the temperature. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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20 pages, 7092 KiB

Open AccessArticle

Characteristics of Acoustic Emission Caused by Intermittent Fatigue of Rock Salt

by Yao Cui, Changjun Liu, Nan Qiao, Siyu Qi, Xuanyi Chen, Pengyu Zhu and Yongneng Feng

Appl. Sci. 2022, 12(11), 5528; https://doi.org/10.3390/app12115528 - 29 May 2022

Cited by 1 | Viewed by 1575

Abstract

This paper compares classic (continuous) fatigue tests and fatigue tests carried out with time intervals of no stress in rock salt using a multifunctional testing machine and acoustic emission equipment. The results show that time intervals of no stress have a strong impact [...] Read more.

This paper compares classic (continuous) fatigue tests and fatigue tests carried out with time intervals of no stress in rock salt using a multifunctional testing machine and acoustic emission equipment. The results show that time intervals of no stress have a strong impact on the fatigue activity of rock salt. In fatigue tests with intervals, the residual strain in circles following an interval (α circles) is generally larger than that in circles before the intervals (β circles). The insertion of a time interval with no stress in the fatigue process accelerates the accumulation of residual strain: the longer the interval, the faster the residual strain accumulates during the fatigue process and the shorter the fatigue life of the rock salt. α circles produce a greater number of acoustic emission counts than β circles, which demonstrates that residual stress leads to internal structural adjustment of rock salt on a mesoscopic scale. During intervals of no stress, acoustic emission activity becomes more active in α circles because of reverse softening caused by the Bauschinger effect, which accelerates the accumulation of plastic deformation. A qualitative relationship between the accumulated damage variable and the time interval is established. A threshold in the duration of the time interval exists (around 900 s). Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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20 pages, 9105 KiB

Open AccessArticle

Dynamic Analysis of the Seismo-Dynamic Response of Anti-Dip Bedding Rock Slopes Using a Three-Dimensional Discrete-Element Method

by Zhanghao Ren, Congxin Chen, Chaoyi Sun and Yue Wang

Appl. Sci. 2022, 12(9), 4640; https://doi.org/10.3390/app12094640 - 5 May 2022

Cited by 10 | Viewed by 1609

Abstract

Earthquakes are a major external factor that induce landslides. In order to systematically study the dynamic effects and failure mechanism of anti-dip bedding rock slopes (the slope trend is the same as the joint trend, while the slope dip direction is opposite to [...] Read more.

Earthquakes are a major external factor that induce landslides. In order to systematically study the dynamic effects and failure mechanism of anti-dip bedding rock slopes (the slope trend is the same as the joint trend, while the slope dip direction is opposite to the joint dip direction) under seismic action (as well as the spatial effects of the structural planes in the anti-dip bedding rock slopes), three-dimensional (3D) discrete-element numerical calculations were performed to analyze anti-dip bedding rock slopes with different slope angles, joint angles, and joint trends subjected to the action of natural seismic and sinusoidal waves. The results were analyzed to investigate the amplification effect, change in Fourier spectrum, failure mechanism, and permanent displacement of the slope under the applied seismic action. The permanent displacement of the slope was calculated using Newmark’s method and the results obtained were discussed and compared with those obtained from a dynamic analysis performed using the 3D discrete-element method. The results showed that the regularity of the spatial distribution of the amplification effect was less clear than that encountered in the planar problem (unidirectional or bidirectional dynamical loading), and this leads to the effect of having an overall rhythmical nature. The seismic wave decays in the high-frequency part from the bottom up of the slope, while the dominant frequency of the seismic wave decreases. The value of the permanent displacement obtained using Newmark’s method is much smaller than that obtained using the dynamic 3D discrete-element analysis approach. The angle between the joint and slope trends has a significant effect on the amplification effect, failure mode, permanent displacement, and stability of slopes subjected to seismic action. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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Review

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11 pages, 2541 KiB

Open AccessReview

Effect of Methane Adsorption on Mechanical Performance of Coal

by Feng Cai, Jingwen Yin and Juqiang Feng

Appl. Sci. 2022, 12(13), 6597; https://doi.org/10.3390/app12136597 - 29 Jun 2022

Cited by 3 | Viewed by 1353

Abstract

Understanding the influence of methane adsorption on coal mechanical properties is an important prerequisite for preventing coal mining and gas mining disasters. In the present research, meager coal and gas coal samples were obtained from Huaneng Yunnan Diandong Energy Co., Ltd. The triaxial [...] Read more.

Understanding the influence of methane adsorption on coal mechanical properties is an important prerequisite for preventing coal mining and gas mining disasters. In the present research, meager coal and gas coal samples were obtained from Huaneng Yunnan Diandong Energy Co., Ltd. The triaxial compression tests were carried out under different methane adsorption equilibrium pressures and confining pressures. The influence laws of different factors on the mechanical properties of coal were analyzed. The results show that the triaxial stress-strain curve of adsorbed methane coal has similar morphology with that of non-adsorbed coal. Under the same confining pressure, the stress-strain curve morphology of coal before and after adsorbing methane is basically the same but the compressive strength of coal after adsorbing methane decreases. The greater the adsorption equilibrium pressure of methane, the smaller the compressive strength of coal. The change in the mechanical properties (compressive strength and elastic modulus) of coal caused by methane adsorption can be described by the Langmuir curve and the correlation coefficient is more than 0.99. Under any stress environment, high-rank coal shows greater strength and lower elastic modulus than low-rank coal, which is mainly due to the existence of a developed cleat system in high-rank coal that provides more conditions for methane adsorption. The research results provide important data-based support for the prevention of coal and gas outbursts. Full article

(This article belongs to the Special Issue Mechanical Properties of Rocks under Complex Stress Conditions)

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