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Open AccessArticle

Using the Morgenstern–Price Method and Cloud Theory to Invert the Shear Strength Index of Tailings Dams and Reveal the Coupling Deformation and Failure Law under Extreme Rainfall

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Sustainability 2023, 15(7), 6106; https://doi.org/10.3390/su15076106 - 31 Mar 2023

Viewed by 505

Abstract

It is difficult to obtain reliable shear strength parameters for the stability analysis and evaluation of tailings dams in an unstable state. In this study, the sensitivity of the shear strength index to the safety factor of a tailings dam was evaluated. The [...] Read more.

It is difficult to obtain reliable shear strength parameters for the stability analysis and evaluation of tailings dams in an unstable state. In this study, the sensitivity of the shear strength index to the safety factor of a tailings dam was evaluated. The cohesion C range of a tailings earth rock dam in an unstable state is determined by the safety factor, and the Morgenstern–Price method is used for inversion. During parameter inversion, uncertainty reasoning is established based on cloud theory, which overcomes the problem that the fuzziness and randomness of the quantitative cohesion value are transferred to the qualitative concept of the safety factor. The results show that the change in cohesion C has a greater influence on the safety factor Fs of the tailings dam, and the value of parameter inversion is 8.6901 kPa. The deformation and failure of tailings dams under extreme rainfall conditions are analyzed by using the modified cohesion C value. The dam toe becomes the main response area of plastic deformation and slowly expands to the interior, showing creep deformation. The displacement field gradually transfers from the accumulated tailings to the tailings dam with the flow direction, causing erosion damage. This study provides a new idea and method for parameter inversion of the shear strength index of tailings dams and provides a reference for the disaster prediction and prevention of tailings dams subjected to extreme rainfall. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Solidification Experiment of Lithium-Slag and Fine-Tailings Based Geopolymers

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Sustainability 2023, 15(5), 4523; https://doi.org/10.3390/su15054523 - 03 Mar 2023

Viewed by 770

Abstract

Based on the pressure of environmental protection, more and more scientific researchers are trying to reuse aluminum–silicon-rich industrial wastes. In this study, activated lithium-slag and lead–zinc tailings were used as raw materials to prepare geopolymers at ratios of 3:7, 1:1, and 7:3. These [...] Read more.

Based on the pressure of environmental protection, more and more scientific researchers are trying to reuse aluminum–silicon-rich industrial wastes. In this study, activated lithium-slag and lead–zinc tailings were used as raw materials to prepare geopolymers at ratios of 3:7, 1:1, and 7:3. These geopolymers were initially cured for 12 h at 25 °C, 50 °C, 75 °C, and 100 °C and were then cured at room temperature to the specified ages. The compressive strength of each group of geopolymers was tested at the ages of 3 days, 7 days, and 28 days. The optimal group of samples was selected, that is, those with a ratio of lithium-slag to lead–zinc tailings of 7:3 and an initial curing temperature of 75 °C. After that, the heavy metal leaching test and porosity analysis test were carried out on the optimal group of samples, and the curing effect was considered to meet the requirements of the Chinese specifications. In addition, in order to reveal the mechanism of the chemical reaction, scanning electron microscopy and X-ray diffraction (XRD) were used to study the microstructure and hydration products of the C3 group cured samples. This study provides a new concept for the reuse of industrial wastes such as lithium-slag and fine-tailings. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Control Technology of Roof-Cutting and Pressure Relief for Roadway Excavation with Strong Mining Small Coal Pillar

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Sustainability 2023, 15(3), 2046; https://doi.org/10.3390/su15032046 - 20 Jan 2023

Viewed by 600

Abstract

In order to solve the problem of serious deformation and failure of surrounding rock and difficult maintenance of gob-side entries with strong mining-induced small coal pillars, taking the A110607 return airway of the Shanwenjiaba Coal Mine as the engineering background, the key parameters [...] Read more.

In order to solve the problem of serious deformation and failure of surrounding rock and difficult maintenance of gob-side entries with strong mining-induced small coal pillars, taking the A110607 return airway of the Shanwenjiaba Coal Mine as the engineering background, the key parameters of roof-cutting and pressure relief control technology for roadway excavation with strong mining-induced small coal pillars were studied by using two-way concentrated blasting roof-cutting and pressure relief technology, combined with theoretical analysis, numerical simulation and a field industrial test. A collaborative control scheme of “roof-cutting pressure relief + anchor cable combined support” is proposed. The test results show that when the height of roof-cutting is 8 m, the angle of roof-cutting is 15°, and when the width of the coal pillar is 3 m, the effect of roof-cutting and pressure relief is the best. Through the field blasting test, it was determined that the blast hole spacing was 800 mm, 321 charge structure was used in the intact roof, and 221 or 211 charge structures were used in the broken roof and geological structure zones. During the driving and strong mining period, the roof and floor movement of the roof-cutting section of the roadway excavation was reduced by about 38% compared with the uncut section, and the deformation of the two sides of the roadway was reduced by about 44% compared with the uncut section. It shows that the collaborative control scheme of “roof-cutting pressure relief + anchor cable combined support” has a good effect on the roadway excavation driving of small coal pillars in strong mining. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study on the Dynamic Stability of an Underground Engineering Rock Mass with a Fault-Slip Seismic Source: Case Study of a URL Exploration Tunnel

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Sustainability 2023, 15(2), 1711; https://doi.org/10.3390/su15021711 - 16 Jan 2023

Viewed by 717

Abstract

The application of fault-slip seismic sources is critical to the success of ground motion dynamic response analysis. Previous research established a finite seismic source to analyze stability in underground engineering. In this paper, a sophisticated numerical method based on the distinct element method [...] Read more.

The application of fault-slip seismic sources is critical to the success of ground motion dynamic response analysis. Previous research established a finite seismic source to analyze stability in underground engineering. In this paper, a sophisticated numerical method based on the distinct element method (3DEC) is proposed to simulate the fault-slip seismic sources of an underground research laboratory (URL) exploration tunnel. Two indices, i.e., the peak ground velocity (PGV) and the strain energy density (SED), are used to analyze the sensitivity of the seismic source types, the seismic source radius, and the rupture velocities of the rock mass dynamic response. The simulation results indicate that a circular seismic source can be used so that the boundary produces a small singularity, with the seismic source having a remarkable influence on the PGV and SED. In addition, we consider that the rupture velocity is more suitable for engineering practices. A simulation method has been developed that allows the rock mass stability of a URL to be further explored. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Strength Estimation of Damaged Rock Considering Initial Damage Based on P-Wave Velocity Using Regression Analysis

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Sustainability 2022, 14(22), 14768; https://doi.org/10.3390/su142214768 - 09 Nov 2022

Viewed by 595

Abstract

High dispersion of rock mass strength causes significant difficulties in strength prediction. This study aims to investigate experimentally the strength prediction model for brittle damaged rock with multiscale initial damage based on P-wave velocity using regression analysis. Intact dolomitic limestone was collected from [...] Read more.

High dispersion of rock mass strength causes significant difficulties in strength prediction. This study aims to investigate experimentally the strength prediction model for brittle damaged rock with multiscale initial damage based on P-wave velocity using regression analysis. Intact dolomitic limestone was collected from a deep metal mine in Southern China. Rock specimens with different initial damage degrees were prepared through the application of uniaxial compressive stress. Both intact rock and damaged rock specimens were tested for P-wave velocity and uniaxial compressive strength (UCS). The test results indicate that the method of prefabricating initial damage to the rock mass through uniaxial compressive stress is feasible. The UCS values of the damaged rock specimens were correlated with the square of the P-wave velocity (linearly positive) and the initial damage (linearly negative). The parameters of the new strength prediction model have a physical significance, and its results are within the upper and lower limits of the 95% confidence interval of the UCS. The strength prediction model considering multiscale initial damage based on P-wave velocity could reasonably predict the strengths of brittle rock masses. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Experimental and Numerical Analysis of Pile–Rock Interaction Characteristics of Steel Pipe Piles Penetrating into Coral Reef Limestone

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Sustainability 2022, 14(21), 13761; https://doi.org/10.3390/su142113761 - 24 Oct 2022

Cited by 1 | Viewed by 886

Abstract

In order to study the characteristics of pile–rock action of steel pipe driven pile in coral reef limestone stratum, coral reef limestone at the China–Maldives Friendship Bridge site was selected to carry out indoor physical and model tests with red sandstone as the [...] Read more.

In order to study the characteristics of pile–rock action of steel pipe driven pile in coral reef limestone stratum, coral reef limestone at the China–Maldives Friendship Bridge site was selected to carry out indoor physical and model tests with red sandstone as the control group. The test outcomes indicate the following: (1) when substantial deformation is permitted, the coral reef limestone has a considerable strength dispersion, a low post-peak stress decrease rate, and a high residual strength, roughly 30% of the peak strength; (2) when the steel pipe pile penetrates the coral reef limestone, the pile top load shows an obvious sawtooth shape, and with the increase in penetration depth, the pile end load of the high-porosity rock sample gradually decreases, and the pile end load of the low-porosity rock sample gradually increases; (3) when the steel pipe pile is penetrated, the strain value of the red sandstone is about twice that of the coral reef limestone at the same position from the steel pipe pile. These findings indicate that the high porosity and heterogeneity cementation characteristics of the coral reef limestone make the extrusion effect during piling significantly less than that of the red sandstone. In addition, the steel pipe pile penetration process is numerically simulated using a four-dimensional discrete spring model method based on the multi-body damage criterion. The numerical simulation results further demonstrate that the pile-side rock fragmentation during steel pipe pile penetration is the primary reason for the lower bearing capacity of steel pipe piles in coral reef limestone stratums. This method provides a novel approach for studying the mechanical properties of reef limestone. The findings can serve as a guide for the design and construction of steel pipe piles in the reef limestone stratum. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study of the Influence of Different Clothing Materials for Mine Ventilation Clothing on Human Body and Microclimate under Clothing

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Sustainability 2022, 14(20), 13460; https://doi.org/10.3390/su142013460 - 18 Oct 2022

Cited by 1 | Viewed by 695

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In order to study the influence of clothing materials on the cooling effect of mine ventilation clothing, the temperatures of human skin and micro-environment under clothing were used as reflection indexes of the cooling effect, and numerical simulations were carried out using fluent [...] Read more.

In order to study the influence of clothing materials on the cooling effect of mine ventilation clothing, the temperatures of human skin and micro-environment under clothing were used as reflection indexes of the cooling effect, and numerical simulations were carried out using fluent software to compare and analyze the temperature changes of human skin and micro-environment under the influence of mine ventilation clothing made of different clothing materials. The results regarding the human skin temperature showed that the modal fiber type resulted in a 0.4 °C lower temperature than the pure cotton type and that the pure cotton type resulted in a 0.6 °C lower temperature than the silica gel type. The temperature comparison of the micro-environment under clothing showed that the modal fiber type resulted in a lower value than the pure cotton type and that the pure cotton type resulted in a lower value than the silicone type; the cooling effect of the three kinds of mine ventilation clothing was modal fiber type > cotton type > silica gel type. In summary, fabric with good permeability and moisture permeability was helpful in improving the cooling effect of mine ventilation clothing. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Using CFD to Simulate the Concentration of Polluting and Harmful Gases in the Roadway of Non-Metallic Mines Reveals Its Migration Law

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Chengyu Xie

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Guanpeng Xiong

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Ziwei Chen

Sustainability 2022, 14(20), 13349; https://doi.org/10.3390/su142013349 - 17 Oct 2022

Cited by 3 | Viewed by 594

Abstract

The green and pollution-free mining of resources has always been a research field that people have focused on. In the process of mining resources, the production of CO, SO₂ and other pollutants directly affects the health of miners and the atmospheric environment [...] Read more.

The green and pollution-free mining of resources has always been a research field that people have focused on. In the process of mining resources, the production of CO, SO₂ and other pollutants directly affects the health of miners and the atmospheric environment in the mining area. Therefore, it is particularly important to deal with and control the polluting gases generated by mining. Taking the underground roadway of a coal mine in Hengdong City, Hunan Province, as the research object, we studied the migration law of pollutant gas there. Comsol software was used to determine the changing state of pollutant gas migration in the roadway, and a simulation model of the wind field and the pollutant concentration field in the roadway under turbulent conditions was established. The results showed that, when the air flow moved to the front face of the roadway, it generated backflow to form a counterclockwise-rotating air flow vortex. Here, the air flow stagnated, hindering the diffusion of pollutants. The gas moved with the air flow in the roadway, and the flow’s velocity decreased in the middle of the roadway, causing pollutants to accumulate. The whole wind field tended to be stable at a plane 25 m from the roadway’s outlet. This indicates that the middle part of the roadway is the place where the polluted gas accumulates, and it is of representative significance to study the concentration of the polluted gas in the roadway in this section. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Destruction Characteristics and Control Countermeasure of Shaft Surrounding Rock Mass in Complex Geological Environment

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Sustainability 2022, 14(20), 13329; https://doi.org/10.3390/su142013329 - 17 Oct 2022

Viewed by 574

Abstract

Increasing construction depth, changeable failure formations, and redistributed stress conditions inevitably make the mechanical response of mining shaft rock mass complicated. The design method and construction technology of deep shaft need to be perfected urgently. We studied the stability and control method of [...] Read more.

Increasing construction depth, changeable failure formations, and redistributed stress conditions inevitably make the mechanical response of mining shaft rock mass complicated. The design method and construction technology of deep shaft need to be perfected urgently. We studied the stability and control method of a main shaft from −930 m located in a deep gold mine. It is concluded that the surrounding rock of the shaft faces conditions including non-high-stressed, high-stressed, and possible instabilities. The failure types include structural plane-controlled failure, deep stress induced failure, rock burst, low confining pressure shear failure, spalling, and frequent conversion of multiple failure. The damages of the surrounding rock mass at −930~−1500 m displayed “ear-shaped” damage, with damage ranges of less than 2.5 m. The shaft temporary reinforcement adopted bolt mResh beam support, in which the length of the bolt was 2.5~3 m, and the row spacing was 1.5 m. The steel type and diameter were determined by the on-site bolt pull test. This temporary support countermeasure plays an important role in preventing shaft deformation and is worth promoting in similar mines. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study on Noise Correction Algorithm of Infrared Emissivity of Rock under Uniaxial Compression

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Dongping Shi

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Jinmiao Wang

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Lichun Xiong

Sustainability 2022, 14(19), 12769; https://doi.org/10.3390/su141912769 - 07 Oct 2022

Viewed by 569

Abstract

In the process of uniaxial loading of rocks, the original temperature information of infrared radiation is easily submerged in the noise signal, which leads to distortion of the obtained infrared radiation response information. In this paper, we propose a multi-band pseudo-emissivity denoising algorithm. [...] Read more.

In the process of uniaxial loading of rocks, the original temperature information of infrared radiation is easily submerged in the noise signal, which leads to distortion of the obtained infrared radiation response information. In this paper, we propose a multi-band pseudo-emissivity denoising algorithm. Based on the basic theory of infrared radiation, by separating the infrared temperature measurement from the emissivity of the measured object, we constructed an infrared multi-band temperature measurement vector group that does not involve the emissivity to reduce the noise interference caused by the infrared temperature measurement results and the emissivity. Under a loading experiment of rock under uniaxial compression, the change of infrared radiation (IR) characteristics with loading was observed. The research results show that the multi-band pseudo-emissivity algorithm could effectively denoise infrared images and, using the denoised rock surface MIRT, AIRT and IRV as indicators, the characteristics of infrared radiation change in the process of uniaxial compression loading and fracturing of real rocks were analyzed. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study on Creep Characteristics of Water Saturated Phyllite

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Yabin Wu

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Jianhua Hu

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Guanping Wen

Sustainability 2022, 14(19), 12508; https://doi.org/10.3390/su141912508 - 30 Sep 2022

Viewed by 621

Abstract

Phyllite is affected by its own bedding, stress environment and water-saturated conditions. There are great differences in its deformation and failure in engineering, and its creep characteristics are an important basis for evaluating the long-term stability of phyllite engineering. Therefore, this study carried [...] Read more.

Phyllite is affected by its own bedding, stress environment and water-saturated conditions. There are great differences in its deformation and failure in engineering, and its creep characteristics are an important basis for evaluating the long-term stability of phyllite engineering. Therefore, this study carried out creep tests of water-saturated phyllite under different bedding angles and confining pressures, studied the coupling effect of factors that affect the creep characteristics of phyllite, and investigated and analyzed the deformation characteristics of a phyllite roadway support on site to provide basic support for phyllite roadway mine disaster control and collaborative mining research. The results showed the following: (1) When the bedding dip angle was 30~60°, under the control of the bedding, the sliding deformation along the bedding suddenly increased under the low-stress condition and the specimen did not undergo structural damage. It could continuously bear multi-level stress and generated creep deformation. In this case, a phyllite roadway should adopt the support method of combining flexibility and rigidity. (2) In the process of multi-stage stress loading, the creep instantaneous stress was directly proportional to the initial stress. When the stress was loaded to 50% of the failure strength, the instantaneous stress tended to be stable and maintained a linear, slightly increasing relationship with the stress. When the bedding angle was 30~60°, the creep deformation accounted for more than 50% of the total deformation. The bedding angles of 0° and 90° were dominated by the instantaneous strain during the stress loading process. For the flexible support of the roadway, the deformation caused by disturbance stress should be fully considered. (3) The uniaxial creep specimen mainly displayed compression shear tensile failure, with a small number of parallel cracks along the main fracture surface. The triaxial creep fracture mode changed to single shear failure. The confining pressure showed greater inhibition of the creep of the specimen with a bedding inclination of 0° and 90°. The strength design of the rigid support should refer to the original rock stress value of the roadway. The creep deformation and failure of the specimen with a bedding inclination of 30~60° were mainly controlled by the bedding. The included angle between the bedding dip angle and the maximum principal stress should be kept within 30~60° as far as possible in the roadway layout. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Numerical Simulation of Gas Extraction in Coal Seam Strengthened by Static Blasting

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Xiaoqiang Zhang

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Fengyuan Zhou

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Jiaxing Zou

Sustainability 2022, 14(19), 12484; https://doi.org/10.3390/su141912484 - 30 Sep 2022

Cited by 6 | Viewed by 768

Abstract

For mines with low permeability and high gas emissions, static blasting technology is used to pre-split the coal seam to increase the permeability and strengthen the gas extraction, which will significantly reduce the occurrence of gas accidents in mines. Taking Wangjialing Coal Mine [...] Read more.

For mines with low permeability and high gas emissions, static blasting technology is used to pre-split the coal seam to increase the permeability and strengthen the gas extraction, which will significantly reduce the occurrence of gas accidents in mines. Taking Wangjialing Coal Mine as the research object, the mathematical model of fluid-solid is established. The numerical simulation software COMSOL is used to simulate the established mathematical model. Simultaneously, the factors affecting the efficiency of static blasting gas extraction are analyzed by adjusting the parameters. The results reveal a more significant drop in gas pressure with increasing time. At 10 d, 30 d, 90 d and 180 d, the extraction efficiency increases by 11.80%, 18.67%, 22.22% and 24.13% in comparison to conventional extraction. In studying the influence of expansion pressure and other factors on gas extraction during static blasting, it is found that the change of negative pressure has little effect on gas extraction. Static blasting can significantly reduce gas pressure and achieve safe coal mining, providing a basis of field application of efficient gas extraction in low gas mines. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Reliability Analysis on Multiple Failure Modes of Underground Chambers Based on the Narrow Boundary Method

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Sustainability 2022, 14(19), 12045; https://doi.org/10.3390/su141912045 - 23 Sep 2022

Viewed by 598

Abstract

This paper proposes to study the stability of underground chambers while taking into account the nonlinear characteristics of geotechnical materials and pore water. According to the upper bound theorem of nonlinear limit analysis and the reliability theory, the failure mode and reliability model [...] Read more.

This paper proposes to study the stability of underground chambers while taking into account the nonlinear characteristics of geotechnical materials and pore water. According to the upper bound theorem of nonlinear limit analysis and the reliability theory, the failure mode and reliability model of underground chambers are established considering the pore water effect. The upper bound solution expression of the surrounding rock pressure in the underground chamber is deduced. The variation law of the surrounding rock pressure is analyzed under different parameters. At the same time, based on the narrow boundary method considering the correlation of multiple failure modes, the influence of different random parameters on the failure probability and reliability index of underground chambers is studied. The results show that the water-level line height, pore water pressure coefficient and Hoek-Brown failure criterion parameter have significant effects on the surrounding rock pressure and underground chamber reliability. In addition, the concept of the safety level is introduced, and the minimum-support force range of the underground chamber with safety level 1 is obtained under different random parameters. The research results can provide a theoretical basis and reference for the structural safety evaluation of underground chambers. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study on Natural Settlement Index Characteristics of Iron-Bearing Tailings Applied to Goaf Filling Treatment

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Sustainability 2022, 14(17), 10739; https://doi.org/10.3390/su141710739 - 29 Aug 2022

Viewed by 669

Abstract

In order to provide a technical basis for the subsequent concentration and utilization of the tailings treatment process in an iron ore mine, and to achieve the objectives of cost reduction and sustainable development, the settling concentration and settling capacity of a tailings [...] Read more.

In order to provide a technical basis for the subsequent concentration and utilization of the tailings treatment process in an iron ore mine, and to achieve the objectives of cost reduction and sustainable development, the settling concentration and settling capacity of a tailings slurry with an initial concentration of 40% in its natural state were tested in conjunction with the pumping supply concentration index of the beneficiation tailings slurry in a metal mine. The test results show that the iron ore tailings particles settle at an overall fast rate: basically, within 10 to 20 min they are able to reach or approach 85 to 99.5% of the final settling state-related index. During the settling process in the fixed container, at first, the clarified water at the top of the tailings slurry is very turbid. With the passage of time, the clarified water gradually becomes blurred and clear from turbidity, and the interface between the slurry and the water gradually becomes clearer. From the phenomena observed during the settling process and the test parameters such as the net increase in clear water and slurry variation, the maximum settling concentration and settling capacity indicators of 50% and 90% can be reached or approached in 5.5 to 7.25 and 10.5 to 15.5 min after settling, and the maximum settling concentration and settling capacity can be reached or approached in 10 to 20 min after the settling process. As the settling tests and observations continued, the relevant settling parameters basically reached the final settling state within the time period of 20 to 1440 min, during which the settling concentration of the tailing sand was 71.33 to 73.42% and the settling capacity was 1.85 to 1.91 g/cm³. It can be judged from the test results that the natural settling of the low concentration tailings slurry can meet the technical specifications required for the filling process, and that the natural settling and concentration of dewatering can save the costs of the relevant facilities and flocculation chemicals, and therefore has good technical and economic feasibility. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Rock Mass Classification Method Based on Entropy Weight–TOPSIS–Grey Correlation Analysis

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Sustainability 2022, 14(17), 10500; https://doi.org/10.3390/su141710500 - 23 Aug 2022

Cited by 2 | Viewed by 741

Abstract

The accurate and reliable classification of rock mass is the basis of a reasonable engineering design. In the Xishan mining region of Sanshandao Gold Mine, three conventional rock mass classification methods of Tunneling Quality Index (Q), Rock Mass Rating (RMR) and China National [...] Read more.

The accurate and reliable classification of rock mass is the basis of a reasonable engineering design. In the Xishan mining region of Sanshandao Gold Mine, three conventional rock mass classification methods of Tunneling Quality Index (Q), Rock Mass Rating (RMR) and China National Standard-basic quality (BQ), were compared in the burial depth area above 780 m, and it was discovered that the classification results of different rock mass classification methods had a low coincidence rate in the deep area; Therefore, this paper adopted entropy weight method, TOPSIS method and grey correlation analysis method to calculate the entropy weight and relative closeness of different methods in different middle sections. The study’s findings revealed that in the deep area, the relative closeness between each classification mass was: RMR > Q > BQ; Based on the above results, the IRMR method with modified RMR was selected for comprehensive analysis, and the concept of importance degree of evaluation index was defined; it was found that the importance degree of evaluation index of in-situ stress loss was the highest, while the importance degree of joint direction was the lowest; The “ETG” rock mass classification method based on “site-specific” is established, which provides a reference for the establishment of deep rock mass classification method. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Study on Stope Stability in Continuous Mining of Long-Dip, Thin Orebody by Room–Pillar Method

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Yanhui Guo

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Yichen Miao

Sustainability 2022, 14(15), 9601; https://doi.org/10.3390/su14159601 - 04 Aug 2022

Viewed by 762

Abstract

In order to analyze the stability of the stope under continuous mining with the room–pillar method for a kind of orebody with a long inclination, but not deep mining, this paper takes the room–pillar method for the continuous mining of a long-inclination orebody [...] Read more.

In order to analyze the stability of the stope under continuous mining with the room–pillar method for a kind of orebody with a long inclination, but not deep mining, this paper takes the room–pillar method for the continuous mining of a long-inclination orebody in the Mengnuo Lead–Zinc Mine, Yunnan Province as the research background. On the basis of the analysis of the stope mechanical model of a long, inclined, thin orebody with room-and-pillar mining, based on numerical simulation, the nature of the change in stress, displacement and the plasticity zone of the roof and pillar during continuous mining along the inclination are systematically analyzed. The results show that as the mining depth increases, the roof subsidence of the stope in the middle of the current operation increases. With the continuous mining of the lower middle section, the roof displacement of the stope will continue to increase with the subsequent mining of the middle section until the end of all stope operations, and the roof displacement of the stope has an obvious cumulative effect. The stress on the roofs and pillars increases with the gradual downward movement of the mining in each level, and the distribution of the plastic zone also expands. It shows that the stope structural parameters that are set according to shallow mining cannot fully meet the requirements of stability and safety in mining a deeper orebody. Therefore, for the mining of a non-deep orebody with a greater tendency to extend, the structural parameters of a shallow stope should not simply be used in the mining of a deeper orebody, but the pillar size should be appropriately increased or the spacing between the room and pillar should be reduced to ensure the stability and safety of the continuous stope. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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Open AccessArticle

Refinement Study on Pressure Relief Zone of Gas Extraction Borehole Considering Roughness

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Sustainability 2022, 14(15), 9541; https://doi.org/10.3390/su14159541 - 03 Aug 2022

Cited by 1 | Viewed by 734

Abstract

Pre-pumping of coal seam gas by gas extraction borehole is an effective measure to manage gas. The existing study concluded that the pressure relief zone of the roadway is difficult to seal, and thus the sealing depth of the gas extraction borehole should [...] Read more.

Pre-pumping of coal seam gas by gas extraction borehole is an effective measure to manage gas. The existing study concluded that the pressure relief zone of the roadway is difficult to seal, and thus the sealing depth of the gas extraction borehole should generally exceed the pressure relief zone of the roadway. Based on the relationship between roughness and GSI, a numerical simulation was carried out with the engineering background of the 22200 machine tunnel of the E8 coal seam of the Sixth Mine of Pingdingshan Tianan Coal Industry Company Limited. The results of numerical simulation and field experiments show that: (1) the quantitative standard of whether the borehole has “air leakage” or whether the surrounding rock cracks around the borehole are connected to the free surface can be characterized by permeability; (2) the variation rate of relative permeability has an inflection point at 2–4 m from the free surface of the roadway wall; (3) the dividing point of whether the surrounding rock cracks around the borehole are connected to the free surface can be set at 6 m, which is located in the pressure relief zone. (4) when the sealing depth of the coal roadway is 6 m and the sealing depth of the rock roadway is 5 m, there is no gas leakage in the borehole, that is, there is an area where a crack is not connected with the free surface of the roadway in the pressure relief zone. Full article

(This article belongs to the Special Issue Mine Disasters Control and Synergetic Mining: Challenges to Mine Sustainability)

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