矿业科学学报

Deep convolutional neural network target detection algorithm for coal mine fault detection

Zhang Chunxiang, Tang Yexiu, Zou Guangui, Zeng Yiwen, Fan Zhuo

2023, 8(6): 733-743. doi: 10.19606/j.cnki.jmst.2023.06.001

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Abstract:
Fault interpretation plays an important role in the field of coal mine safety. The development of neural network gives rise to many intelligent seismic data interpretation and processing schemes based on neural network algorithm. This study ①selected the Faster R-CNN target detection algorithm more suitable for fault recognition by comparing different deep convolutional neural network target detection algorithms. ②tested AlexNet, residual network ResNet50 and ResNet101 feature extraction networks through seismic forward modeling with various geological characteristics. It is found that ResNet101 feature extraction network has better performance in fault detection. ③constructed a fault detection model based on the preferred ResNet101 feature extraction network and Faster R-CNN target detection algorithm, and detected the actual seismic data. Results show that the object detection algorithm based on deep convolutional neural network shows satisfactory generalization ability in fault detection. It could improve the fault interpretation efficiency, and has potential in application.

Microscopic distribution of fluid in Sulige tight sandstone gas reservoir and its influencing factors

Zhang Hanpeng, Ren Dazhong, Zhang Rongjun, Qu Le, Li Tian, Li Qihui

2023, 8(6): 744-757. doi: 10.19606/j.cnki.jmst.2023.06.002

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Abstract:
The Lower Shihezi Formation in the eastern part of Sulige gas field has high water content, where the exploitation of tight sandstone gas reservoir is considerably affected by the characteristics of fluid occurrence. Specifically, this study analyzed the porosity, permeability, lithology, pore throat heterogeneity and connectivity and their effects on fluid occurrenceby rock and ore identification, porosity and permeability analysis and NMR centrifugation. Results show that: ①the tight sandstone reservoir in the study area shows poor pore flow capacity, and bound water saturation. The flow capacity is closely related to the gas flow pressure difference (centrifugal force). ②Intercalations play a key role in controlling flow capacity. Abundant kaolinite content indicates that the reservoir has better connectivity, larger pore size and stronger overall pore water flow capacity. Illite has a strong water-holding capacity, which could easily cause capillary obstruction and limited flow capacity. ③The gas flow pressure difference (centrifugal force)is exponentially related to the pore diameter of reservoir pore water flow. ④The critical pore throat radius of the effective reservoir space is 0.089μm, and the mobile water saturation is 23.95% in Xiashihezi Formation in the eastern part of Sulige gas field.

Rock physics experiment and rock physical modeling of hot dry rock under high temperature

Gao Wanli, Zhao Jingtao, Wang Huawei

2023, 8(6): 758-767. doi: 10.19606/j.cnki.jmst.2023.06.003

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Abstract:
Currently, the investigation and monitoring of geothermal energy face significant challenges, and a lack of understanding regarding the variations in physical parameters of hot dry rock reservoirs with temperature is a crucial factor. In this study, 29 hot dry rock samples from the Gonghe Basin in Qinghai Province were subjected to high-temperature petrophysical experiments to analyze the changing patterns of physical parameters with temperature. Results show that: ①The density of rock samples gradually decreases with temperature, albeit with an attenuation range of less than 1%. ②The temperature change exerts a substantial influence on the P-wave velocity and S-wave velocity of the samples, resulting in significant attenuation between 120 ℃ and 180 ℃, with respective reductions of approximately 1 500 m/s and 800 m/s. ③A peak magnetic field intensity, seven times greater than at room temperature, is reached at 120 ℃. ④The resistivity fluctuates with increasing temperature, whose values ranges from 10 to 25 Ω·m. Based on these experimental results and with the combination of the classical Gassmann equation and fluid substitution models, this study made a quantitative analysis on the impacts of porosity and temperature variations on longitudinal wave velocity. The outcomes indicate that a porosity of 0.025 resulted in a decrease of approximately 600 m/s in the longitudinal wave velocity with increasing temperature, whereas a porosity of 0.1 caused a decrease of approximately 1 000 m/s under the same conditions.

Mechanics of tunnel deformation in water-rich fault zone and double-gradient grouting NPR compensation countermeasures

Tao Zhigang, Zhou Zicong, Yang Xiaojie, Huo Shusen, Sun Jihao, Du Zhifeng

2023, 8(6): 768-779. doi: 10.19606/j.cnki.jmst.2023.06.004

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Abstract:
Tabaiyi Tunnel is located in the eastern foothill of the Tibetan Plateau, crossing a multi-stage fault tectonic zone, and its surrounding rock is weak and broken, and its strength plummets when it encounters water. The peripheral rock under the original design scheme has a large deformation of meter scale, and there are disasters such as twisted arch, elevated arch bulge and sudden mud and water surge. In order to solve the problem of peripheral rock fragmentation in the tunnel in the water-rich fault zone, firstly, the deformation mechanism of the tunnel in the water-rich fault zone and its transformation were analyzed through mineral composition analysis, point load test and ground stress test; through the bearing capacity test of the grouted peripheral rock with ungrouted, regular grouted and double-gradient grouted, it was determined to adopt the double-gradient grouted process for the anchoring of NPR anchor ropes; then, the optimal anchor rope number was derived from the numerical simulation and on-site test; finally, through the on-site application, the optimal anchor rope number was obtained. Finally, the reliability of the double gradient grouting and high preload long and short NPR anchor cable support system is verified through field application. Based on monitoring data, the results of the study can be used as a reference for the control of large deformation hazards in similar tunnels with water-rich fault zones.

Experimental study on mechanical behavior of external prestressed FRP reinforced concrete beams

Wu Lili, Ma Yuanyuan, Yang Jiaqi, Wu Haipeng

2023, 8(6): 780-790. doi: 10.19606/j.cnki.jmst.2023.06.005

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Abstract:
This study proposes to investigate the failure characteristics and load-bearing performance of external prestressed composite reinforced concrete beams by conducting a three-point loading test on 12 full FRP reinforced concrete beams. These external prestressed concrete beams were reinforced with carbon fiber reinforced polymer(CFRP), while the stress reinforcement and stirrup were made of glass fiber reinforced polymer(GFRP). Specifically, the study compares the impact of prestress level, shear span ratio, and concrete type on the bearing capacity of GFRP reinforced concrete beams. derives an expression for flexural bearing capacity to account for the effect of stress increment of prestressed tendons, and is verified by experimental results. The test results indicate that the failure of non-prestressed FRP reinforced concrete beams is primarily governed by deformation, whereas applying prestress can shift the failure mode from deformation control to bearing capacity control. The mid-span deflection of the concrete beam is directly proportional to the increase in prestress. The bearing capacity of FRP beams decreases with an increase in shear span ratio, with particularly significant effect on cracking load. The effect of concrete type on the cracking load of prestressed beams surpasses its impact on the ultimate load, while it exerts minimal influence on cracking and ultimate load of non-prestressed beams. The calculated results for the bearing capacity of prestressed FRP reinforced concrete beams derived in this study align well with the measured values.

Experiment research on unfrozen water content and pore characteristic of cement improved soil under freeze-thaw cycle

Liu Bo, Gao Rong, He Yanqing, Zhao Lu, Li Dongyang, Sun Yanding

2023, 8(6): 791-802. doi: 10.19606/j.cnki.jmst.2023.06.006

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Abstract:
Grouting with cementitious materials is a commonly-recognized measure to control the freezing and thawing deformation of artificial freezing strata. This study investigated the unfrozen water content of silty clay with different cement content under freeze-thaw condition, as well as the pore characteristics of the silty clay before and after freeze-thaw cycle based on nuclear magnetic resonance. It analyzed pore characteristics variation patterns of cement improved soil before and after freeze-thaw cycle and the micro-mechanism of freeze-thaw damage through scanning electron microscopy and mercury intrusion porosimetry. Results showed that: ①With the same water content, the increase of cement content would lead to the initial increase and subsequent decrease in the sensitivity to temperature of water molecule magnetization in the pores. ②When the cement content is between 0%~10% and at the same temperature during thawing process, the increase of cement content would lead to the initial decrease and subsequent increase of the unfrozen water content in the frozen soil. ③Compared with the silty clay without cement, cement improved silty clay shows little changes in its pores before and after the freeze-thaw cycle. The pore characteristics and microstructure of improved silty clay with cement content of 5% are less affected by freeze-thaw cycle. This research can provide references for the study of freeze-thaw resistance of improved soil and the stability control of strata frost heave and thaw settlement in artificial frozen engineering.

Mechanism and prevention of typical coal burst disaster at the working face of Hongqinghe coal mine

Liu Wenchao, Zhao Yixin

2023, 8(6): 803-816. doi: 10.19606/j.cnki.jmst.2023.06.007

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Abstract:
This study aims to tackle the problem of frequent coal-rock dynamic events caused by local stress concentration in deep mining working face under high static stress environment. Specifically, by taking the deep working face of Hongqinghe Mine located in Xinjie Mining Area as an example for analysisthis paper investigates the geological conditions of No. 3^-1coal seam that are affected by the mining method and the coal rock dynamic disaster events occurred during mining; utilizes numerical simulation to simulate the mining stress field and energy field of the stope; analyzes the potential coal burst instability area and mechanism of coal burst gestation and catastrophe in the stope during the mining of the No. 3^-1103 working face; probes into the sources of catastrophic stress and influencing factors of coal-rock disasters in dangerous areas, puts forward targeted prevention and control measures. Results show that: ① the roof strata structure, goaf and coal pillar are the key factors influencing coal burst in the stope during the mining of the No. 3^-1103 working face; ② the simulation results indicatethe location and characteristics of the coal burst instability area in the stope of the No. 3^-1103 working faces, as well as the simulation outlines 5 strong coal burst areas and 11 medium coal burst areas presented in the stope; ③ Measures are proposed for coal burst during mining from the perspective of cutting off the dynamic load source, reducing static load stress concentration, and blocking the transmission of high concentration stress. Detailed measures include implementing multi-source prevention and control in areas with high static or high static+dynamic loads, implement pre-pressure off-load measures prior to mining, and local risk relief and coal burst prevention and reduction treatments during mining.

Molecular simulation on competitive adsorption characteristics of CH₄/O₂/N₂ gas in lignite

Zhang Tonghao, Chen Mingyi, Tian Fuchao, Liu Huizu, Zhang Hao, Wang Shuo

2023, 8(6): 817-827. doi: 10.19606/j.cnki.jmst.2023.06.008

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Abstract:
This study intends to explore the influence of temperature and molar ratio on the competitive adsorption of CH₄/O₂/N₂ gas in coal. It probed into the competitive adsorption characteristics of CH₄/O₂ and N₂/O₂ binary mixed gas in Xiaolongtan lignite of Yunnan under different temperatures (303.15~383.15 K)and pressures (0~480 kPa)through grand canonical Monte Carlo (GCMC)and molecular simulation methods. Results show that : ① Within the range of test temperature and pressure, temperature will inhibit the adsorption of CH₄, O₂ and N₂ by coal, and the adsorption capacity of coal to three gases is CH₄>O₂>N₂. ② The selectivity coefficient of CH₄/O₂ adsorption is basically independent of the gas molar ratio, and shows decrease with the increase of temperature. The adsorption selectivity of N₂/O₂ on coal under different molar ratios was not significantly related to temperature and molar ratio. ③ With the increase of adsorption capacity, the isosteric adsorption heat of any component in the binary mixed gas shows linear increase. Under the same adsorption capacity, larger molar ratio of CH₄/O₂ and N₂/O₂ would lead to lower adsorption heat. However, when the adsorption capacity of CH₄ is less than 0.029 mmol / g, the isosteric adsorption heat of CH₄ gas shows little correlation with the molar ratio. The research reveals the influence mechanism of competitive adsorption behavior of CH₄ and air on low temperature oxidation of coal.

Study on mechanical and seepage characteristics of water-saturated coal under rapid cold and heat shock by liquid nitrogen freeze-thaw and microwave heat injection

Ma Heng, Hou Shuangrong, Qi Xiaohan, Wang Pin, Liu Yang, Wang Xiaoqi

2023, 8(6): 828-837. doi: 10.19606/j.cnki.jmst.2023.06.009

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Abstract:
This study proposes to explore the coal mechanics and seepage characteristics under the coupling of water-saturation, freeze-thaw and different temperatures. The original coal of 9105 working face in Wangzhuang Coal Mine was taken as the research object, and non-contact digital image processing was used to carry out the triaxial loading test of the coal rock under the conditions of liquid nitrogen freeze-thaw and microwave heat injection. Results showed that: ① in the original coal samples after freeze-thaw, water-saturated, and water-saturated freeze-thaw conditions and gradient temperature treatment, there is increase in the compressive strength, modulus of elasticity, Poisson's ratio, and shear strain value of the coal rock; ② the original coal rock in the compression density, elasticity, yield and destruction of the four stages of the stress concentration phenomenon shows no obvious developmental changes, but by water-saturated, water-saturated freeze-thaw, water-saturated freezing and thawing conditions of 100 ℃ and 150 ℃ temperature treatment, the local stress of the specimen concentrates in the destruction phase with obvious amplification; ③ compared with the initial permeability of the original coal rock, the initial permeability of the coal sample underwent a small increase of 1.44×10^-3μm² after the liquid nitrogen freeze-thaw treatment. After the water-saturated liquid nitrogen freeze-thaw, water-saturated liquid nitrogen freeze-thaw treatment at 50 ℃ and 100 ℃, there is more significant increase in the initial permeability of the coal rock, and after the water-saturated liquid nitrogen freeze-thaw treatment at 150 ℃, the initial permeability of the coal sample underwent a significantly higher increase and reaches 7.40×10^-3μm². The study provide references for increasing the permeability of gas in deep low-permeability coal beds, which could improve the efficiency of downhole gas extraction.

Experimental study on the ratio between ti-bearing blast furnace slag-iron-based full tailing sand and cement in cementitious filling

Li Jielin, Li Ao, Hao Jianzhang, Xü Jiye, Zhang Liangbing

2023, 8(6): 838-846. doi: 10.19606/j.cnki.jmst.2023.06.010

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Abstract:
This study investigated the optimal ratio and mechanical properties of iron-based full tailing sand(IFT)and cement(P.O42.5R)as experimental materials, with the addition of the Ti-bearing Blast Furnace Slag(TBS), in full tailing sand cemented filling material. The physical and chemical properties of TBS, including particle size gradation composition and chemical composition, were analyzed. Filling specimens were prepared with sand-cement ratios of 1∶4, 1∶6, and 1∶8, and TBS replacement ratios of 40%, 50%, 60%, 70%, and 80%. The uniaxial compressive strength of the filling specimens was measured after curing for 7, 14, and 28 days. The experimental results demonstrated a positive correlation between the compressive strength of the filling and the curing time. Additionally, under the same curing time, the uniaxial compressive strength of the filling increased with the increase of the sand-cement ratio. With an increase in the replacement percentage of TBS, the strength of the filling initially increased and then decreased at 28 days. Notably, when the TBS replacement ratio was 50%, the compressive strength of the filling with ratios of 1∶8, 1∶6, and 1∶4 after 28 days of curing was 1.8 MPa, 2.5 MPa, and 4.0 MPa, respectively. All of these values exceeded the strength of the specimens without TBS, indicating that the addition of TBS significantly improved the compressive strength of the filling at 28 days. The research results demonstrate that TBS can be developed as a cementitious material for mine backfill, thereby reducing the cost of mine filling.

Synthesis of micron-particle-size HZSM-5 zeolite with different Si/Al ratio and its catalytic activity for toluene methanol alkylation reaction

Pan Xu, Huang Xin, Wang Ruizhuang, Zhang Haiyong, Wei Hui, Xu Deping, Liu Yi

2023, 8(6): 847-855. doi: 10.19606/j.cnki.jmst.2023.06.011

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Abstract:
HZSM-5 molecular sieve is one of the commonly used catalysts for the alkylation of toluene with methanol to para-xylene (PX). This study introduces a one-step method to directly prepare microscale HZSM-5 catalysts with suitable pore structure and acidity. Specifically, this paper combined crystal seed regulation of the morphology of HZSM-5 and adjusted the Si/Al ratios of the precursor solution for HZSM-5 synthesis to regulate the acidic phase of the HZSM-5. It analyzed the phase composition, pore structure parameters, microstructure, and acidity of HZSM-5 molecular sieve through X-ray diffraction, N₂ adsorption desorption, SEM, NH₃ temperature programmed desorption, pyridine infrared spectroscopy, etc. This study investigated the catalytic performance of HZSM-5 in the alkylation of toluene with methanol to PX, and explored the effects of pore structure and acidity on the catalytic performance. Results indicate that in the hydrothermal crystallization method, the crystal seeds and aluminum content in the synthesis solution have a significant impact on the acidity and morphology structure of the HZSM-5 molecular sieve. The HZSM-5 (150)molecular sieve catalyst with 5μm grain size exhibits 60% PX selectivity and 11% toluene conversion rate in the evaluation reaction of toluene methanol alkylation due to its longer diffusion path and more suitable acidic sites. By fine-tuning the pores and acidic sites of HZSM-5 molecular sieve, the selectivity for PX has been effectively improved, providing new methods and approaches for the design of shape-selective catalysts.

Preparation, classification, hydration mechanism and durability of magnesium-based cementing material

Hu Jie, Wang Yan, Zhang Shaohui, Chang Tianfeng, Sun Linlin

2023, 8(6): 856-867. doi: 10.19606/j.cnki.jmst.2023.06.012

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Magnesium-based cementing material is a new type of cementitious material based on active MgO. It features rapid solidification, early strength and fire resistance, exhibiting significant advantages in repair and emergency repair projects. This study divided magnesium-based cementitious materials into three types according to the differences in calcination temperature of MgO and blending solution : magnesium oxychloride cement, magnesium oxysulfate cement, magnesium phosphate cement. We conducted detailed discussion and review of their hydration mechanism and durability. The hydration of magnesium oxychloride cement lies in the hydration of ternary system of MgO, MgCl₂ and H₂O. The hardened system of magnesium oxysulfate cement shows low strength due to the existence of free MgSO₄ in the hydration process. The hydration rate of magnesium phosphate cement delayed owing to the overlapping of exothermic of MgO solution and sharp reaction between MgO and phosphate, which leads to excessive hydration and over-concentrated heat release. Carbonation reduces the pores contents, optimizes the internal pore structure, and improves the strength and durability of magnesium-based cementitious materials. The magnesium-based cementitious materials have poor water resistance, among which no unified understanding has been reached as to the reasons for magnesium oxychloride cement. For magnesium oxysulfate cement, the unreacted MgO reacts with water to form Mg(OH)₂, and the volume expansion leads to the cracking of the hardened matrix. In the case of magnesium phosphate cement, the phosphate can lead to the dissolution of hydration products and unreacted MgO.

Labor structure transformation and career remodeling of intelligent coal mine

Zhao Li, Li Jun

2023, 8(6): 868-878. doi: 10.19606/j.cnki.jmst.2023.06.013

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The labor force structure of intelligent coal mine has undergone profound changes as the coal industry transforms from traditional coal mines to intelligent ones. In this light, this study ① reviews the characteristics of the labor force in intelligent coal mine, ② analyzes the interaction mechanism of labor force and labor tools, ③ builds an adaptation model of labor force and labor tools. Specifically, it analyzes the deficiencies existing in the present personnel structure in intelligent coal mine construction from the perspective of labor quality structure, personnel training scale, regulations related to "intelligent replacement", coal mine data management professionals, and term shifts of posts in intelligent coal mines. This paper proposes detailed scheme and measures for career reshaping in intelligent coal mines, namely restructuring intelligent mining personnel structure, creating new posts and new types of work, updating policies and regulations, improving industry image and employee happiness, and improving talent training system.

2023 Vol. 8, No. 6