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19 pages, 6082 KiB

Open AccessArticle

Prediction of the Water Inrush Risk from an Overlying Separation Layer in the Thick Overburden of a Thick Coal Seam

by Daolei Xie, Zhongwen Du, Chenghao Han, Jie Han, Jiuchuan Wei and Jiulei Yan

Sustainability 2023, 15(18), 13988; https://doi.org/10.3390/su151813988 - 20 Sep 2023

Cited by 3 | Viewed by 1006

Abstract

With the expansion of coal mining westward in China, water inrush from seam roofs has become a prominent safety problem during mining. The roof rock of the coal seam in the Shilawusu coal mine has the characteristics of a double-layer structure, and the [...] Read more.

With the expansion of coal mining westward in China, water inrush from seam roofs has become a prominent safety problem during mining. The roof rock of the coal seam in the Shilawusu coal mine has the characteristics of a double-layer structure, and the overlying separation space formed in the mining process of the coal seam poses a risk of water inrush. To ensure the safety of coal mine production, considering the geological and hydrogeological data of the mining area, the core recovery rate, lithologic assemblage index, key aquifer thickness, hydrostatic head and lithologic structure index of the Zhidan Formation are selected as evaluation indexes. The index weights are calculated based on the attribute hierarchical model and coefficient of variation methods, and subjective and objective preference coefficients are introduced to determine the ranking of comprehensive indexes. The catastrophe progression method is improved, and a zoning prediction model for water inrush risk is established by the improved catastrophe progression method. The results show that only a tiny part of the mining area is in danger, and most areas are in the safe and transition zones. The model realizes the prediction of the risk of water inrush from the overlying separation layer in the study area and provides a theoretical basis for the prevention and control of water inrush from the overlying separation layer in coal mining. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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17 pages, 25985 KiB

Open AccessArticle

Experimental Study on Mechanical Properties and Acoustic Emission Characteristics of Dry and Water-Saturated Soft Rocks under Different Dynamic Loadings

by Lugen Chen, Dong Wang, Yujing Jiang, Hengjie Luan, Guangchao Zhang and Bin Liang

Sustainability 2023, 15(17), 13201; https://doi.org/10.3390/su151713201 - 2 Sep 2023

Cited by 5 | Viewed by 1232

Abstract

Studying how soft rocks behave dynamically in water-rich settings is vital for ensuring sustainable coal extraction from deep water-saturated soft rock mines. A dynamic disturbance loading system utilizing creep-impact dynamics was employed to analyze the mechanical traits and acoustic emission behaviors of both [...] Read more.

Studying how soft rocks behave dynamically in water-rich settings is vital for ensuring sustainable coal extraction from deep water-saturated soft rock mines. A dynamic disturbance loading system utilizing creep-impact dynamics was employed to analyze the mechanical traits and acoustic emission behaviors of both dry and fully saturated soft rock. Expanding on uniaxial compression tests as a foundational framework, additional experiments involving dynamic disturbances and acoustic emission observations were carried out on the aforementioned soft rock samples. These experiments encompassed a spectrum of cyclic disturbance amplitudes ranging from 2 kN to 10 kN. Experimental results indicated the following: (1) during dynamic disturbance, the hysteresis loop exhibits a “sparse to dense” variation. When subjected to the same number of disturbances, the hysteresis loop takes on a pointed leaf-like shape, which increases with the amplitude of the disturbances. (2) The pinnacle of intensity and the elastic modulus of the samples, when exposed to diverse amplitudes of disturbances, can be categorized into a strengthening phase and weakening phase. The reinforcement effect is highest for both samples under the effect of a perturbation of 4 amplitudes. (3) Under the action of disturbances at various amplitudes, the acoustic emission signals from the samples can be classified into four stages. In all stages, the maximum acoustic emission signals exhibited by the desiccated samples surpass those emanated from the saturated samples. In the fluctuation period (II), dry and saturated samples exhibit a cyclic strengthening effect, which becomes more pronounced as the amplitude increases. The study results offer theoretical support for understanding deformation and instability mechanisms in roadways of deep water-saturated soft rock mines, which is essential for ensuring sustainable coal resource development. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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15 pages, 15266 KiB

Open AccessArticle

Study on the Instability Mechanism of Coal and Rock Mining under a Residual Coal Pillar in Gently Inclined Short-Distance Coal Seam with the Discrete Element

by Chuanwei Zang, Jia Zhou, Miao Chen, Feng Bai and Zhengyang Zhao

Sustainability 2023, 15(7), 6294; https://doi.org/10.3390/su15076294 - 6 Apr 2023

Cited by 3 | Viewed by 1799

Abstract

The collapse of overlying rocks caused by the instability of residual coal pillars during lower coal seam mining significantly impacts its safety. This paper focuses on the gentle dipping coal seam group and utilizes the discrete element method (DEM) as the basis to [...] Read more.

The collapse of overlying rocks caused by the instability of residual coal pillars during lower coal seam mining significantly impacts its safety. This paper focuses on the gentle dipping coal seam group and utilizes the discrete element method (DEM) as the basis to comprehensively consider multiple factors through orthogonal experiments. In so doing it reveals the influence mechanisms of various factors on mining at a close distance under a residual coal pillar. Firstly, the process of lower coal seam mining under residual coal pillars in gently-dipping coal seams was simulated and analyzed based on a case study at the Baoping coal mine. Comparing the evolution characteristics of coal–rock fractures, stress changes, and displacement changes during the mining process reveals the mechanism of the joint instability of the lower coal seam, interlayer rock, coal pillars, and overlying strata under the disturbed conditions of lower panel mining. Secondly, an orthogonal simulation experiment was established using the width of the coal pillar and the thickness of the lower coal seam as variables. By comparing the development process of cracks, stress distribution, and rock displacement under different conditions, the research results indicate that the width of coal pillars has an impact on the maximum amount of coal pillar subsidence, while the thickness of the underlying coal seam has an impact on the time of subsidence, when h_d ≥ 4.2 m (h_j/h_d ≤ 4) and w ≤ 14 m (w/h_m ≤ 2), a large-scale collapse of the overlying strata of the coal pillar occurs. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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23 pages, 5604 KiB

Open AccessArticle

Study on Mine Earthquakes Mechanism and Ground Vertical Well Hydraulic Fracturing Shock Absorption in Thick Hard Rock Mine

by Xiaoguang Shang, Sitao Zhu, Fuxing Jiang, Jinhai Liu, Xiufeng Zhang, Xiang Sun, Chao Wang, Yang Chen, Bo Xu, Jiajie Li and Xiaocheng Qu

Sustainability 2023, 15(6), 5122; https://doi.org/10.3390/su15065122 - 14 Mar 2023

Cited by 2 | Viewed by 1447

Abstract

Mine earthquakes are serious disasters in coal mines, especially in extremely thick hard strata. This study investigates the occurrence mechanism of fracture-type mine earthquakes in thick hard strata. Hydraulic fracturing by ground vertical well was used for shock absorption. Dongtan coal mine was [...] Read more.

Mine earthquakes are serious disasters in coal mines, especially in extremely thick hard strata. This study investigates the occurrence mechanism of fracture-type mine earthquakes in thick hard strata. Hydraulic fracturing by ground vertical well was used for shock absorption. Dongtan coal mine was taken as a case study. Field investigation, theoretical analysis, industrial tests, and field monitoring were used for revealing the mechanism. First, the mechanical model of extremely thick, hard strata under horizontal concentrated stress was established. The fracture step equation and energy release equation of extremely thick hard rock were derived by semi-inverse solution and variational method. Then, the mechanical model of extremely thick hard rock after hydraulic fracturing by ground vertical well was established. The relationship between the spacing of the ground vertical well and the maximum magnitude of mine earthquakes was deduced. The fracturing well in the 6306 working face was designed for controlling the maximum mine earthquake magnitude. Results show that the increases in the breaking distance of the thick hard rock layer led to an increase in the released energy during the fracture, and an enhancement of the magnitude of the mine earthquake. By applying hydraulic fracturing technology using the ground vertical shaft, the occurrence frequency and total energy of mine earthquakes above 1.5 ML in the 6306 working face decreased by 54.55% and 81.22% than that in 6304 working face, and reduced by 70% and 84.98% than that in 6305 working face. Hydraulic fracturing technology by ground vertical well can significantly reduce the frequency of fracture-type and the total energy of mine earthquakes in extremely thick and hard strata. However, it can not prevent and control the occurrence of back-transition mine earthquakes and slip-type mine earthquakes. The obtained results can provide a basis for the fracture-type mine earthquake mechanism and fracturing shock absorption technology in coal mines with super-thick hard strata. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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18 pages, 57919 KiB

Open AccessArticle

Macroscopic Mechanical Properties of Brittle Materials with a 3D Internal Crack Based on Particle Flow Simulations

by Suling Chang, Zaiquan Wang and Yu Cong

Sustainability 2023, 15(5), 4563; https://doi.org/10.3390/su15054563 - 3 Mar 2023

Cited by 1 | Viewed by 1444

Abstract

Pre-existing cracks significantly influence the macro-mechanical properties of rock. The macro-mechanical properties and crack propagation process of brittle materials with a 3D internal crack were investigated with PFC^3D simulation in this paper. To determine the micro-parameters, the influence of micro-parameters on the [...] Read more.

Pre-existing cracks significantly influence the macro-mechanical properties of rock. The macro-mechanical properties and crack propagation process of brittle materials with a 3D internal crack were investigated with PFC^3D simulation in this paper. To determine the micro-parameters, the influence of micro-parameters on the macro-mechanical properties and ultimate failure mode was discussed. SJM’s parameters had little influence on the macro-mechanical properties and ultimate failure mode. Peak axial stress was changed greatly by strength parameters and friction coefficient, and the macro-elastic modulus was influenced greatly by Young’s modulus and changed slightly with other parameters. The failure mode changed gradually with all micro-parameters except Young’s modulus, which had a strong but irregular impact on it. The peak stress was 138 MPa in the simulation of the sample with a 3D internal crack, which agreed well with the experimental result (137 MPa). The crack propagation process can be divided into three stages: 17% of total crack was generated in the initial stage; 76% of the total crack was propagated when main failure surface coalesced; finally, the failure surface expanded downwards and caused the sample to be destroyed. Cracks initially appeared near the end of the lower major axis of the internal crack, which was in agreement with experimental results. The results demonstrated that PFC^3D is a reliable method to simulate the failure process of brittle materials with internal cracks. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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16 pages, 7218 KiB

Open AccessArticle

Study on Floor Heave Characteristics and the Control Method of Gob-Side Entry Driving in Weakly Cemented Soft Rock

by Xuerui Yang, Fenghai Yu, Chengfu Ma, Tao Zhang, Bo Wang and Xin Zhao

Sustainability 2023, 15(5), 3969; https://doi.org/10.3390/su15053969 - 22 Feb 2023

Cited by 4 | Viewed by 1241

Abstract

Aiming at the problems of large deformation, long duration, and difficult control of floor heave in gob-side entry driving in weakly cemented soft rock, this paper takes the weakly cemented soft rock mining area in Western China as the engineering background, and studies [...] Read more.

Aiming at the problems of large deformation, long duration, and difficult control of floor heave in gob-side entry driving in weakly cemented soft rock, this paper takes the weakly cemented soft rock mining area in Western China as the engineering background, and studies the characteristics and mechanism of floor heave in gob-side entry driving in weakly cemented soft rock by means of a field investigation, physical component analysis, mechanical property tests of the surrounding rock, and the stress monitoring of the surrounding rock. The classification control method of floor heave is put forward, and field tests are conducted. The results show that: (1) The floor heave characteristics of the dynamic change in the floor heave peak position of gob-side entry driving from the coal pillar side to the mining side are obtained through field observation. (2) Based on the analysis of field data and laboratory test data, it is concluded that the stability time of the overlying strata in gob-side entry driving is about 8 to 12 months. The main internal cause of roadway floor heave is the low load resistance of weakly cemented soft rock. High stress and strong disturbances are the main power sources of strong floor heave. The mechanism of floor heave affected by dynamic lateral abutment pressure is summarized, and the classification control method of floor heave is proposed. (3) The gob-side entry driving support technologies of “adjusting excavation deployment” and “surrounding rock pressure relief and improving support” are proposed. Through field tests, the floor heave can be effectively controlled. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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17 pages, 4795 KiB

Open AccessArticle

Study on Bursting Liability of Coal-like Material with Pores and Anchors Based on Impact Kinetic Energy Characteristics

by Donghai Jiang, Chuanyang Jia, Yanfei Wang, Zeyu Wang, Wanpeng Huang, Hengjie Luan and Pu Wang

Sustainability 2023, 15(4), 3820; https://doi.org/10.3390/su15043820 - 20 Feb 2023

Cited by 1 | Viewed by 1600

Abstract

Drilling unloading, and bolt support are widely used in the practice of coal mine roadway engineering as the means of impact prevention and support. However, the evaluation index of intact coal body is still used in bursting liability evaluation, and the evaluation results [...] Read more.

Drilling unloading, and bolt support are widely used in the practice of coal mine roadway engineering as the means of impact prevention and support. However, the evaluation index of intact coal body is still used in bursting liability evaluation, and the evaluation results obtained do not match with the actual dynamic phenomena in the field, resulting in inaccurate evaluation results and even bringing serious impact accidents. In this paper, uniaxial compression and uniaxial loading/unloading tests are conducted on specimens in different states, and common evaluation indexes are used to evaluate the bursting liability of specimens in different states, and the impact kinetic energy of crushed blocks during uniaxial compression is calculated. Based on this, the bursting liability criterion based on the impact kinetic energy of the crushed block is established and the common bursting liability evaluation index is modified. The bursting liability obtained by the bursting liability discrimination criterion based on the impact kinetic energy of the crushed block is more consistent with the laboratory dynamic phenomena. Therefore, the bursting liability evaluation results based on the impact kinetic energy of the crushed block are more consistent with the actual engineering. And the numerical simulation results verify the correctness of the bursting liability criterion based on the impact kinetic energy of the crushed block. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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12 pages, 5211 KiB

Open AccessArticle

Experimental Study on the Influence of Different Loading Rates on Fatigue Mechanical Properties of Sandstone

by Jinsong Zhang, Yu Lu, Jianyong Pang, Hao Wang and Hezan Du

Sustainability 2023, 15(1), 566; https://doi.org/10.3390/su15010566 - 29 Dec 2022

Cited by 1 | Viewed by 1938

Abstract

Underground rock engineering often encounters long-term cyclic loading and unloading. Under the influence of this effect, the mechanical characteristics of rocks will inevitably change, which will affect the stability and safety of underground engineering. Therefore, it is necessary to study the fatigue characteristics [...] Read more.

Underground rock engineering often encounters long-term cyclic loading and unloading. Under the influence of this effect, the mechanical characteristics of rocks will inevitably change, which will affect the stability and safety of underground engineering. Therefore, it is necessary to study the fatigue characteristics of rocks under a certain period of action. With an RDL series electronic creep relaxation testing machine, fatigue loading and unloading tests of sandstone at different loading rates were carried out, followed by uniaxial compression on the samples. The study shows that the stress–strain curves of the uniaxial compression specimens have three stages: a compaction pore fracture stage, an elastic deformation stage, and an unstable fracture developing to failure stage. The stress–strain curves of the samples with a certain number of cycles of loading and unloading give the thinning and dense phenomenon, and the axial upper limit strain and axial cumulative residual strain gradually decrease as the loading rate increases. With the increase, the uniaxial compressive strength of the reloaded samples increases gradually, which is higher than the ordinary uniaxial compressive strength. In the process of cyclic loading and unloading, the internal particles of the sample present fracture and reorganization of the fragile structure and, at the same time, compaction stability. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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14 pages, 10395 KiB

Open AccessArticle

The Influence of Cross-Section Shape on Failure of Rock Surrounding the Main Tunnel in a Water-Sealed Cavern

by Yu Cong, Heyi Liu, Xiaoshan Wang, Defu Guo, Liliang Han, Yi Zhao and Lilei Zou

Sustainability 2023, 15(1), 424; https://doi.org/10.3390/su15010424 - 27 Dec 2022

Cited by 1 | Viewed by 1524

Abstract

The influence of cross-section shape on rock stability was investigated by designing a similar model test and numerical simulation using particle flow code (PFC). The test results showed that the left- and right-hand sides of the entrance are subjected to tension, mainly forming [...] Read more.

The influence of cross-section shape on rock stability was investigated by designing a similar model test and numerical simulation using particle flow code (PFC). The test results showed that the left- and right-hand sides of the entrance are subjected to tension, mainly forming vertical cracks or oblique cracks with a large dip angle. The vicinity of the entrance is subjected to the shear effect and the overall failure of the model is brittle in the similar test. Mesoscopic fractures mainly appear as tensile fractures, and a small number of shear fractures are found in the vicinity of the entrance. A long narrow coalescent-fracture zone is separately formed at the left- and right-hand sides of the entrance when approaching peak load in PFC test. Stress concentration occurs at the end of the long axis of the elliptic cross-section. The stress is high at the arch foot and spandrel of a horseshoe-shaped cross-section and a coalescent fracture zone formed at the arch foot on the right-hand side caused the tunnel to fail. The ovoid-shaped and vertical-wall-arched cross-sections are under significant tension, owing to the force chains distributed along the tunnel wall, show a large included angle with the tunnel wall. From the perspective of bearing capacity, a circle is the best section. From the perspective of failure mode, the horseshoe-shaped section is more suitable for use in corresponding practical engineering. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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18 pages, 5061 KiB

Open AccessArticle

Critical Instability Criterion of Large-Diameter Shafts in Deep Topsoil Based on Ultimate Strain Analysis

by Yu Cong, Zhulan Liu, Xiaoshan Wang, Qiang Chen, Lei Wang, Fang Kang and Erdi Abi

Sustainability 2022, 14(21), 14552; https://doi.org/10.3390/su142114552 - 5 Nov 2022

Cited by 2 | Viewed by 1380

Abstract

Shaft stability plays an important role in mine safety. Most of the previous studies focused on the stress analysis of shafts using monitoring data. Since the shaft wall state in the deep topsoil stratum is still not clear, the ultimate analysis method is [...] Read more.

Shaft stability plays an important role in mine safety. Most of the previous studies focused on the stress analysis of shafts using monitoring data. Since the shaft wall state in the deep topsoil stratum is still not clear, the ultimate analysis method is adopted to study the bearing capacity and the strain of a large-diameter shaft wall in Yanzhou coal mine. First, the bearing capacity of the shaft wall is discovered. The value of the auxiliary shaft, main shaft and ventilating shaft is 22.22 MPa, 22.07 MPa and 21.73 MPa, respectively. Then, the ultimate strain of the shaft wall is obtained; the designed ultimate strain corresponding to those shafts is 1.468‰, 1.458‰ and 1.435‰, while the working ultimate strain is 2.078‰, 1.800‰ and 2.638‰, respectively. Since the working values are greater than the design values, the shaft walls need to be reinforced, which is consistent with the field situation. Finally, numerical analysis based on the finite difference method (FDM) is performed to investigate the evolution process of ultimate strain on the shaft wall. The results show the ultimate strain could provide a theoretical basis for safe service and management of a large-diameter shaft in a deep topsoil area. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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19 pages, 19226 KiB

Open AccessArticle

Analysis of Impact Tendency and Sensitivity of Fractured Rock with Different Crack Arrest Measures

by Shiming Liu, Fukun Xiao, Tan Li and Bo Zhang

Sustainability 2022, 14(21), 13833; https://doi.org/10.3390/su142113833 - 25 Oct 2022

Cited by 4 | Viewed by 1643

Abstract

Crack propagation leads to rock instability and failure, which seriously influence the safe and efficient operation of coal mines. According to the characteristics of fracture development and expansion, this paper takes a fractured rock with different crack numbers as the research background and [...] Read more.

Crack propagation leads to rock instability and failure, which seriously influence the safe and efficient operation of coal mines. According to the characteristics of fracture development and expansion, this paper takes a fractured rock with different crack numbers as the research background and studies the effects of the grouted arrest measure, anchored crack arrest measure, and grouted anchored arrest measure on the mechanical properties, energy evolution, crack expansion, and progressive instability of the fractured rock. The sensitivity of different crack arrest measures to the peak strength, elastic modulus, total crack number, and impact tendency of the fractured rock are analyzed based on the sensitive percentage. The experimental results show that the more cracks in the rock, the greater the increase of peak stress of grouted rock and grouted anchored rock, and the smaller the increase of peak stress of anchored fractured rock. With the increase of the crack number, the total crack number in anchored fractured rock specimens gradually decrease, the total crack number in grouted rocks, and grouted anchored rock specimens gradually increase. The anchored fractured rock with more cracks produces a lower total crack number when it is destroyed. The grouted rock and grouted anchored rock with more cracks produce a higher total crack number when it is destroyed. The pre-peak energy of anchored single-fractured rock is larger, the pre-peak energy of grouting multi-fractured rock is larger, and the grouted rock has a strong impact tendency. The grouted arrest measure is an important sensitive parameter to the impact energy index; the anchored crack arrest measure is the primary sensitive parameter to the peak stress, elastic modulus, and total crack number; and the grouted anchored arrest measure is an important sensitive parameter to the elastic modulus. The research results of this paper provide some guidance on the selection of crack arrest parameters and scheme design in practical rock engineering. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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20 pages, 5278 KiB

Open AccessArticle

Research on the Height of the Water-Conducting Fracture Zone in Fully Mechanized Top Coal Caving Face under Combined-Strata Structure

by Donghai Jiang, Yinfeng Tang, Wanpeng Huang, Keke Hou, Yi Luo and Jiangwei Liu

Sustainability 2022, 14(21), 13781; https://doi.org/10.3390/su142113781 - 24 Oct 2022

Cited by 3 | Viewed by 1297

Abstract

In order to study the development height of the water-conducting fracture zone in a fully mechanized top coal caving face. The E2311 working face of Gaohe Coal Mine was chosen as the research object, and the combined-strata structure and the rock layer synergistic [...] Read more.

In order to study the development height of the water-conducting fracture zone in a fully mechanized top coal caving face. The E2311 working face of Gaohe Coal Mine was chosen as the research object, and the combined-strata structure and the rock layer synergistic movement mechanism were determined by combining engineering geological investigation and theoretical analysis. The height of the water-conducting fracture zone at the working face was calculated based on the combined-strata structure, and then the theoretical results were verified by numerical simulation and field measurement. The results show that after the coal seam is extracted from the working face, the movement of the overlying rock layers is in the form of bending and sinking movement of the rock layer group as a unit. Each rock layer group is controlled by a supportive lower layer with greater thickness and strength, driving the upper layers of weaker rock layers to synchronize and coordinate the movement; the sinking curvature is the same, after the lowermost support layer is bent and broken, its overlying weaker rock layers will move and break at the same time. The height of the water-conducting fracture zone of the working face were obtained by theoretical calculation, numerical simulation, and field measurements, which are 83.82 m, 84.3 m, and 86.6 m, respectively. The results are nearly consistent, thus the prediction of the height of the water-conducting fracture zone under the combined-strata structure is more accurate. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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17 pages, 4696 KiB

Open AccessArticle

Study on Elastoplastic Damage Coupling of Reservoir Mudstone Considering Permeability Change

by Wenjun Jing, Songhua Mei, Yanan Zhao and Yu Zhang

Sustainability 2022, 14(20), 13507; https://doi.org/10.3390/su142013507 - 19 Oct 2022

Viewed by 1428

Abstract

Mudstone, a common complex medium in oil and gas reservoirs and with widely distributed micro-pore and micro-fissures, is liable to produce significant damage evolution and plastic deformation under high buried depth stress environments. Based on the analysis of the physical characteristics, the elastoplastic [...] Read more.

Mudstone, a common complex medium in oil and gas reservoirs and with widely distributed micro-pore and micro-fissures, is liable to produce significant damage evolution and plastic deformation under high buried depth stress environments. Based on the analysis of the physical characteristics, the elastoplastic damage coupling mechanical characteristics of mudstone in a high buried depth reservoir for oil and gas engineering are discussed. Firstly, conventional triaxial compression tests under different confining pressures were performed to calculate the damage variable and obtain the damage evolution. The damage evolution included the elastic damage stage, the plastic-dominated elastoplastic damage coupling stage and the damage-dominated elastoplastic damage coupling stage. Secondly, a coupled elastoplastic damage mechanical model for mudstone was proposed, which was based on the degradation of the damage stiffness and plastic flow caused by the plastic and damage internal variables and considered the elastic damage coupling and elastoplastic damage coupling during the loading process. Thirdly, the elastoplastic damage coupling mechanical characteristics of mudstone were simulated. The simulation results are in good agreement with the experimental results, which reflects well the mechanical characteristics of mudstone, including the transition from volume compression to expansion, plastic hardening, damage softening and residual strength, etc. Finally, based on the relevant research results, a permeability evolution model of mudstone based on the damage was proposed, and the secondary development was carried out based on ABAQUS. UMAT and USFLD subroutines were compiled, and seepage–stress coupling simulation verification was carried out. The relevant results provide a reliable basis for engineering theory research and stability analysis of deep mudstone reservoirs. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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15 pages, 2695 KiB

Open AccessArticle

Addressing Random Variations in MWD Penetration Rate with the DPM Algorithm

by Siyuan Wu, Xuefan Wang and Zhongqi Quentin Yue

Sustainability 2022, 14(20), 13456; https://doi.org/10.3390/su142013456 - 18 Oct 2022

Cited by 4 | Viewed by 1572

Abstract

Measurement While Drilling (MWD) is an in situ technique for the assessment of ground conditions. It records the drilling parameters of a drilling machine when its drill bit is penetrating into new geomaterials below the bottom of a drill hole. Its penetration rate [...] Read more.

Measurement While Drilling (MWD) is an in situ technique for the assessment of ground conditions. It records the drilling parameters of a drilling machine when its drill bit is penetrating into new geomaterials below the bottom of a drill hole. Its penetration rate along drill hole depth, however, has various random variations. Such random variations are inconsistent with the fact that the geomaterials in the ground have piece-wise homogeneity. Many methods have been adopted to filter and normalize the random variations in penetration rate for ground characterization. However, they have not completely resolved the issue and obtained the piece-wise homogeneous distribution of geomaterials in the ground. This paper uses the time-series algorithm of the Drilling Process Monitoring (DPM) technique to remove the random variations in MWD penetration rate. It further obtains the piece-wise constant variations in the newly addressed DPM penetration rate along the drill hole depth. With this algorithm, the DPM penetration rate is consistent with the fact that ground geomaterials have the property of piece-wise homogeneous distribution. Consequently, the piece-wise constant variations in DPM penetration rate can be used to characterize the strength variations in geomaterials along the drill hole depth to substantially upgrade the MWD technique for ground investigation. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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16 pages, 3447 KiB

Open AccessArticle

Analysis of the Factors Affecting the Construction of Subway Stations in Residential Areas

by Peng Dai, Song Han, Xuxu Yang, Hui Fu, Yanjun Wang and Jianjun Liu

Sustainability 2022, 14(20), 13075; https://doi.org/10.3390/su142013075 - 12 Oct 2022

Cited by 5 | Viewed by 2787

Abstract

To design a more suitable scheme under different conditions so that subway stations can play their role better, this study investigated the construction elements of subway stations in residential areas. Metro stations in residential areas are generally located at the intersection of urban [...] Read more.

To design a more suitable scheme under different conditions so that subway stations can play their role better, this study investigated the construction elements of subway stations in residential areas. Metro stations in residential areas are generally located at the intersection of urban roads. As the “handover space” of the city, the construction principle should be based on people’s experience. As the core basis for traffic planning and future operation management, construction of subways in residential areas should take into consideration factors such as trip volume, distribution, and mode selection of residents, and be determined based on such mathematical models as the unit factor method, gravity model, and disaggregated analysis method. Station site selection is based on the point, line, and surface elements, and the importance of a station in the line network is judged by degree and betweenness centrality; the accessibility of the line network is determined by connectivity. In this study, the influencing factors of residential area subway station construction are divided into construction elements and site selection. Internal construction elements of stations include station entrances and exits, escalators, ticket machines, and transfer routes, and the conclusion of the mathematical model is used to select or give opinions about the internal construction elements of the subway. The point, line, and surface elements and the connection relationship between the subway and buses are used to determine the site selection of the subway. Furthermore, this paper discusses the three elements that affect the construction of the subway, comprehensively considers the functional requirements of the subway, and makes reasonable adjustments to each element. Finally, the requirements for the elements of the subway construction are determined. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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17 pages, 17182 KiB

Open AccessArticle

Lugeon Test and Grouting Application Research Based on RQD of Grouting Sections

by Sheng Ren, Yanlin Zhao, Jian Liao, Qiang Liu and Yang Li

Sustainability 2022, 14(19), 12748; https://doi.org/10.3390/su141912748 - 6 Oct 2022

Cited by 12 | Viewed by 2841

Abstract

Rock quality designation (RQD) and permeability coefficient are important reference indexes for grouting application. Based on the readily available RQD, RQD is found to have no relationship with the depth of rock stratum, and a method for calculating the mean RQD (RQD_m [...] Read more.

Rock quality designation (RQD) and permeability coefficient are important reference indexes for grouting application. Based on the readily available RQD, RQD is found to have no relationship with the depth of rock stratum, and a method for calculating the mean RQD (RQD_m) of long stratum is proposed, which is applied to the calculation of RQD of grouting sections. Through Lugeon and grouting tests on the grouting sections, RQD_m of the grouting sections is found to be directly related to the average permeability coefficient, permeability, and units of grouting per amount of rock mass. It is found that RQD_m has a symmetrical relationship with permeability and grouting volume as well as a negative exponential correlation with unit grouting volume and average permeability coefficient. According to the curve of RQD varying with depth, the grouting amount at different depths can be obtained by using the fitting formula of unit grouting amount and RQD_m. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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17 pages, 4208 KiB

Open AccessArticle

Risk Assessment of Water Inrush from Coal Seam Roof Based on Combination Weighting-Set Pair Analysis

by Daolei Xie, Jing Han, Huide Zhang, Kai Wang, Zhongwen Du and Tianyu Miao

Sustainability 2022, 14(19), 11978; https://doi.org/10.3390/su141911978 - 22 Sep 2022

Cited by 13 | Viewed by 1677

Abstract

When exploiting Jurassic-era coal resources in Northwest China, there are risks of water inrush and sand burst disasters from coal seam roofs. To improve the safety of coal mining, it is imperative to accurately and objectively evaluate the water inrush risk of sandstone [...] Read more.

When exploiting Jurassic-era coal resources in Northwest China, there are risks of water inrush and sand burst disasters from coal seam roofs. To improve the safety of coal mining, it is imperative to accurately and objectively evaluate the water inrush risk of sandstone aquifers from coal seam roofs and to reasonably and effectively prevent and control water disasters. In this paper, the 221 mining area of the Shilawusu Coal Mine was considered. By combining the basic geological condition data, hydrogeological condition data, and drilling data in the area studied, four main control factors, including the equivalent thickness of sandstone, the lithology coefficient of sandstone, the interbedded coefficient of sand and mud, and the core recovery rate, were selected as evaluation indexes for predicting the water inrush risk from the coal seam roof. A hierarchical prediction and discrimination model of water inrush risk based on combination weighting-set pair analysis was established. The combination weighting method, which is based on the sum of squared deviations, was used to optimize the subjective and objective weight values obtained by the improved analytic hierarchy process and entropy weight methods. By applying set pair analysis theory, the comprehensive connection degree was determined using the set pair connection degree function that was constructed with 31 instances of drilling data in the study area. Then, the risk grade of each drilling data instance was evaluated by the confidence criterion of set pair analysis to calculate the water inrush risk evaluation index. Finally, the obtained index was combined with the borehole pumping test data and the discharging test data to partition the water inrush risk from the coal seam roof. The results indicated that most of the 221 mining area is safe, and the small transitional and dangerous areas are only in the central and northern regions. Based on the combination weighting-set pair analysis method, the water inrush risk from the coal seam roofs in the study area was accurately and objectively classified by a discrimination model. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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19 pages, 2745 KiB

Open AccessArticle

Dynamic Mechanical Behaviors and Failure Mechanism of Lignite under SHPB Compression Test

by Yanqi Song, Hongfa Ma, Jiangkun Yang, Junjie Zheng, Juntao Yang and Wei Bao

Sustainability 2022, 14(17), 10528; https://doi.org/10.3390/su141710528 - 24 Aug 2022

Cited by 9 | Viewed by 2080

Abstract

There is an obvious impact effect of on-site blasting on the slope coal mass of open-pit mines, so it is of great significance to study the dynamic mechanical response characteristics of coal rock for slope stability control. In this paper, first, the mineral [...] Read more.

There is an obvious impact effect of on-site blasting on the slope coal mass of open-pit mines, so it is of great significance to study the dynamic mechanical response characteristics of coal rock for slope stability control. In this paper, first, the mineral composition and microstructure of lignite from open-pit mine are analyzed, and it is found that the content of non-organic minerals in lignite such as clay accounts for more than 24.40%; meanwhile, the rock sample has obvious horizontal bedding characteristics and mainly micro pores and transition pores inside; further, there are obvious banded areas with high water content in the rock, which has the same extending direction as the beddings. Based on the SHPB test system, the dynamic compression tests of lignite with different impact velocities are carried out. The results show that there is a significant hardening effect caused by the increase of strain rate on the dynamic mechanical parameters of rock samples, and the stress–strain curve has obvious “double peak” characteristics; meanwhile, the macroscopic crack of the rock appears at the first stress peak and disappears after further compression until the interlayer fracture occurs; further, the fracture fractal dimension of lignite increases linearly with the impact velocity, revealing that the fragmentation of rock samples increases gradually. In addition, with the increase of impact velocity, the input energy and dissipated energy of rock samples increase linearly, while the elastic property increases slowly and at a low level. The bedding characteristics of lignite and the wave impedance difference between the layers cause the high-reflection phenomenon in the process of stress-wave propagation, and then produce the obvious tensile stress wave in the rock sample, which finally results in the interlayer fracture failure of the rock. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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23 pages, 6205 KiB

Open AccessArticle

Analysis of Factors Influencing Mining Damage Based on Engineering Detection and Machine Learning

by Lintian Miao, Zhonghui Duan, Yucheng Xia, Rongjun Du, Tingting Lv and Xueyang Sun

Sustainability 2022, 14(15), 9622; https://doi.org/10.3390/su14159622 - 4 Aug 2022

Cited by 6 | Viewed by 2189

Abstract

The direct results of mining damage are overburden fracture and surface subsidence, which may induce groundwater seepage and surface vegetation degradation. Therefore, it is essential to research the factors and mechanisms influencing mining damage. Based on the geological characteristics of the Xiaobaodang minefield [...] Read more.

The direct results of mining damage are overburden fracture and surface subsidence, which may induce groundwater seepage and surface vegetation degradation. Therefore, it is essential to research the factors and mechanisms influencing mining damage. Based on the geological characteristics of the Xiaobaodang minefield in the Yushen Mine area in China, the engineering detection of fractured zone height (FZH), sampling tests of rock mechanical properties, and field measurements of the surface settlement were carried out. Firstly, the factors influencing the FZH were screened by correlation analysis and partial correlation analysis. Next, a model for predicting the maximum height of the fracture zone with the BP neural network (BPNN) was established and trained with Python. Finally, the FLAC^3D numerical simulation experiment was adopted to reveal the variation law of overburden stress during coal mining, and the relationship between stress and overburden fracture was analyzed. The results show the following: When the average mining thickness in the study area is 5.8 m, the maximum height of the fractured zone is 157.46 m, and the maximum surface subsidence is 3715 mm. Further, the mining thickness, mining depth, the compressive strength of overburden, the width of the working face, and the mining velocity are the main factors affecting the maximum height of the fractured zone. Additionally, the goodness of fit of the BPNN model can reach 97.22%, meaning that it can effectively predict the maximum height of the fractured zone caused by coal mining. Finally, the area where the stress changes markedly above the goaf is the area where the fractures develop rapidly. Meanwhile, there is a positive correlation between the surface subsidence and the FZH. The research results obtained provide new ideas for reducing mining damage and will be helpful for the green and sustainable development of the mine. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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25 pages, 8210 KiB

Open AccessEssay

A Numerical Method for Evaluating the Collapse of High-Steep Scarp Slopes Based on the Bonded Block Model–Discrete Fracture Network Model

by Zening Sun, Shili Qiu, Siquan Yan and Zaiquan Wang

Sustainability 2023, 15(21), 15672; https://doi.org/10.3390/su152115672 - 6 Nov 2023

Cited by 2 | Viewed by 1283

Abstract

Geotechnical engineering works in deep-incised valleys or open-pit mining areas often encounter high-steep scarp slopes with a slope angle greater than 75°. This type of slope directly threatens the safety of construction personnel, so assessing their stability is essential to ensure construction safety. [...] Read more.

Geotechnical engineering works in deep-incised valleys or open-pit mining areas often encounter high-steep scarp slopes with a slope angle greater than 75°. This type of slope directly threatens the safety of construction personnel, so assessing their stability is essential to ensure construction safety. The natural geometry of high-steep scarp slopes possesses complexity in terms of geometric morphology, structural features of rock mass, and occurrence mechanisms of collapse. There is little research and less emphasis on the evaluation of the collapse risk of high-steep scarp slopes. In particular, the fracture of intact rock or rock bridges is generally ignored in the analysis of collapse processes. A bonded block model (BBM)–discrete fracture network (DFN) coupling characterization model for the high-steep scarp slope is proposed based on a high-steep scarp slope containing dominant joint sets on the left bank of the dam site of the Huangzangsi Water Conservancy Project (Qinghai Province, China). By using the model, the complex geometric forms of the surface of the high-steep scarp slope are quantified, and the fracture process of falling rock masses as well as the controlling effect of dominant joints on the collapse of the scarp slope are revealed. A strength reduction method based on the BBM–DFN model is constructed, and the safety factor of the collapse-prone scarp slope is evaluated. The research results show that (1) the BBM–DFN model can be used to describe the local collapse process; (2) the occurrence of dominant joints plays an important part in controlling the collapse process; (3) there are differences in the safety factor of the scarp slope with different coupling methods; the collapse and failure modes also differ. For safety considerations, the safety factor of the scarp slope on the left bank of the dam site area is determined to be 1.85. The research findings can be used to guide the safety assessment of high-steep scarp slopes and the formulation of both collapse risk prevention and control measures to ensure construction safety in high-steep scarp slope areas. Full article

(This article belongs to the Special Issue Deep Mining Engineering in Sustainability)

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