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Multi-scale failure mechanics of rock in mining engineering
Zuo Jianping, Sun Yunjiang, Liu Haiyan, Yu Meilu, Lei Bo, Song Hongqiang, Wen Jinhao
2021, 6(5): 509-523.   doi: 10.19606/j.cnki.jmst.2021.05.001
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Abstract:
In mining engineering, the multi-scale failure behavior of surrounding rock under the complex stress environment is a fundamental influencing factor of disasters. This paper systematically summarizes our recent ten years' research progress of rock multi-scale failure mechanics, including macro/meso rock failure mechanics, roadway surrounding rock control and rock strata movement. In terms of laboratory research scale of rock mechanics, the propagation process of rock meso-crack under the thermal-mechanical coupling effect was studied by using the SEM test system, which reveals the meso-fracture mechanism of rock. The macro failure and mechanical properties of rock, coal and coal-rock combined body were experimentally investigated under different loading and unloading conditions. A non-linear model of coal and rock mass macro failure was established. In terms of roadway failure scale, the stress gradient failure mechanism of the surrounding rock of roadway was revealed, the theory of uniform strength support in deep roadway was established, which guides the direction of roadway support. Then the full-space collaborative control technology of roadway was proposed and applied on site. In terms of rock fracture mechanics and movement scale, the evolution of roof fracture modes of different thicknesses was studied by experiments, and four roof fracture modes and fracture mode partitions were obtained. Based on the theory of key strata, the analogous hyperbola model and the inner and outer analogous hyperbola model of overburden movement caused by mining were proposed. The evolution of the analogous hyperbola model with the variation of the key layer position and the dip angle of coal seam was analyzed. The above results will provide theoretical and technical support for the prevention and control of coal mining disasters in our country.
Review of research on steel support with corrugated webs
Wu Lili, Wang Hui, Xu Xiang, Wu Haipeng, Zhao Weiping
2021, 6(5): 524-535.   doi: 10.19606/j.cnki.jmst.2021.05.002
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The research progress on optimistic analysis and ultimate bearing capacity of the conventional metal supports, such as mine I-beam, U-shaped steel and concrete filled steel tubes, is summarized. It especially focused on introducing a new type of steel support with corrugated webs. The advantages of steel support with corrugated webs in bearing capacity and economy compared with traditional supports, the global stability bearing capacity and local stability of the steel support structure with corrugated webs in different roadway profiles are introduced herein. It also reviews the research work and achievements on the yieldable connecting configuration, as well as the interaction between the support and the surrounding rock. It can be concluded that the prominent advantages of the support with corrugated web are its high supporting capacity and light weight, which is economical and greatly reducing the labor intensity. The two types of yieldable connecting components (high-strength bolts and wedge sleeves) are developed, which can solve the eccentricity issue of traditional one, besides, the surrounding rock load on the supports can be reduced through connection yielding and pressure relief, which could improve the stability and service life of the steel supports with corrugated webs. The research achievements have vital reference significance to the future development of new support structures for coal mine roadways with rock bursts.
Flexural floor heave mechanism and floor corner piles control technology in soft rock roadway
Guo Dongming, Kang Xinchao, Lu Zhiying, Chen Qiyu, Zhang Wei, Zhao Zhifeng, Cao Yanpeng
2021, 6(5): 536-547.   doi: 10.19606/j.cnki.jmst.2021.05.003
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In order to solve the problem of flexural floor heave support under the condition of weak floor with high stress, the supporting form of concrete filled steel tube floor corner pile is put forward. The failure characteristics of the surrounding rock of the flexural floor are studied on the research background of the 18-floor south track roadway of the fourth level in Xing'an Mine. Based on the deflection theory of slab and the virtual work principle, the instability criterion of flexure-type floor under the condition of floor corner pile support is given, and the support mechanism of foundation pile is studied. The results show that the high stress and insufficient strength of surrounding rock are the main reasons for the instability of roadway floor and weakening the stress of floor rock and strengthening the floor rock are the key to control the flexural floor heave. The sectional geometry parameters and pile spacing of piles are the key design parameters to determine the ultimate resistance. The pile length should include the embedding depth of 0.4 R ~ 0.6 R(R is the plastic zone radius), and the pile should be laid through the equivalent circle radius of the roadway section or in a vertical direction. Based on the above research, a field test was carried out on floor corner pile. The field monitoring results show that the pile foundation stress of the floor has a good barrier effect on the compressive stress of the surrounding rock of the roadway floor, and the deformation of the floor and the two sides can be well controlled, and the stability of roadway can be significantly improved. This control technology can provide a reference for roadway floor heave support under similar conditions.
Study on the dynamic evolution characteristics of deformation and collapse of the extra-thick hard roof
Wang Hongwei, Deng Daixin, Jiang Yaodong, Shi Ruiming, Yang Guozhen, Zhang Xiaohai
2021, 6(5): 548-557.   doi: 10.19606/j.cnki.jmst.2021.05.004
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Yima coal field has an extra-thick hard rock strata, which is the main cause of many dynamic disasters in the mining area. Based on the mining face 21221 of Qianqiu mine in Yima coal field, Henan Province, China, this paper studies the movement characteristics of extra-thick hard roof during the advancement of working face by similar simulation and numerical analysis methods, carries out laboratory test on bursting liability of roof strata, analyzes the dynamic evolution law of collapse vertical displacement of extra-thick hard roof, and obtains the relationship between mining-induced stress and movement of the roof. The results show that: the failure of extra-thick hard roof could be divided into three stages: quiet period, stable failure period and collapse period. The vertical displacement of roof collapse changes a little during the quiet period, and is basically concentrated in the goaf during the stable failure period, showing a trapezoidal decreasing trend upward. However, it will develop rapidly upward during the collapse period. The movement law of extra-thick hard roof presents an unstable dynamic change phenomenon, that is separation, instantaneous subsidence, separation closure, intermittent stability, instantaneous collapse and compaction. With the advancement of the working face, the deformation and movement of extra-thick hard strata lead to the continuous and unstable subsidence pressure exerting on the stope. The structural instability of the extra-thick hard roof leads to severe mutation of ground pressure on the stope and sudden decrease of mining-induced stress, and that is an important inducement for the occurrence of rock burst.
Study on dynamic crack initiation and propagation behavior of surrounding rock of adjacent roadway
Yang Liyun, Zhang Fei, Chen Siyu, Hu Huanning, Wang Ziyang, Lin Changyu
2021, 6(5): 558-568.   doi: 10.19606/j.cnki.jmst.2021.05.005
Abstract(76) HTML(43) PDF(13)
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In order to study the mechanical behavior characteristics of dynamic crack initiation and propagation of surrounding rock of adjacent roadway under impact load, with the help of a new digital laser dynamic caustics experimental system, a rock-like medium material PMMA was used to make a double-section roadway model for impact tests, and the crack propagation simulation was carried out based on the ABAQUS numerical simulation platform. The results show that when the pre-crack deflection angle α of adjacent sections is 45°, 22. 5°, 0°, -22. 5°, -45°, the dynamic stress intensity factor are different when the cracks were initiated. The dynamic stress intensity factor change after crack initiation has a "platform section" with a duration of about 160 μs. When the right crack gradually moves away from the left cross-section, the crack propagation speed of left crack after initiation will increase. When the dynamic crack initiation and propagation of the double-section roadway, the adjacent sections will affect the dynamic stress intensity factor and propagation speed to a certain extent. When the tip of the right crack is close to the left crack, the latter's crack initiation toughness is reduced, that is, it is easier to crack.
Recent development and prospects of energy-absorbing bolt in underground engineering
Jiang Bei, Wang Qi, Wei Huayong, Xin Zhongxin, He Manchao, Wu Wenrui, Ma Fenglin, Xu Shuo, Wang Yetai
2021, 6(5): 569-580.   doi: 10.19606/j.cnki.jmst.2021.05.006
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There are many challenges in the process of underground engineering construction, such as high stress, extremely soft rock, strong mining and other complex conditions. The surrounding rock is difficult to control and its deformation is serious due to the stress concentration and energy accumulation, leading to frequent roof fall, collapse, rock burst and other accidents. Anchor bolt is the main support mode of underground engineering chamber. In order to absorb energy released by surrounding rock deformation and control the deformation of surrounding rock, it is necessary to develop energy-absorbing bolt with high constant resistance, high elongation and high prestress. This paper summarizes and analyzes the development process, performance test and field application of energy-absorbing bolt. Energy-absorbing bolt absorb energy by structural slip and material deformation. According to the working principle, the energy-absorbing bolt can be divided into three types: rod structure type, mechanical structure type and body material type. Compared with structural energy-absorbing bolt, the structure of material energy-absorbing bolt is relatively simple, which can give full play to the mechanical properties of material. The author's team developed a new constant resistance energy-absorbing bolt, and carried out static tensile and dynamic impact tests. The results show that the bolt has high strength, high elongation and high energy absorption characteristics, which can meet the requirements of surrounding rock control under complex conditions. In the future, the test, design, construction and acceptance standards of the constant resistance energy-absorbing bolt should be formulated to realize its application in underground engineering in different fields such as mine, traffic, municipal engineering and water conservancy.
Research progress of shield opening technology in urban metro
Li Dongyang, Dai Baicheng, Liu Bo, Fu Chunqing
2021, 6(5): 581-590.   doi: 10.19606/j.cnki.jmst.2021.05.007
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When shield machine is driving for a long distance, it is often forced to stop due to obstacles or excessive wear of tools, which is one of the main risks of shield construction. In order to summarize the research progress of shield opening technology in urban metro, the paper systematically summarizes the two technical ideas of normal pressure opening and pressurized opening, and summarizes the principle, risk factors and principles of shield opening under two technical conditions. Combined with typical engineering examples, the application scope, key technology, advantages and disadvantages of conventional compressed air and saturated gas method with pressure opening technology are analyzed and summarized. The engineering application of atmospheric pressure opening technology and atmospheric pressure cutter disc tool changing technology for soil grouting and freezing reinforcement is summarized. Finally, combined with the current research progress and the development trend of large diameter underwater shield in China, the paper analyzes the technical challenges faced by the shield opening in the future, discusses the direction of further research, and provides a reference for the development of shield opening technology in China.
Research on theoretical calculation model of shield segments floating amount and floating control measures
Yang Zhiyong, Yang Xing, Zhang Changwang, Sun Zhengyang, Jiang Yusheng, Shao Xiaokang
2021, 6(5): 591-597, 605.   doi: 10.19606/j.cnki.jmst.2021.05.008
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The floating of the shield segment will cause the segment to be misaligned and damaged, reducing the overall structural strength, waterproof performance and service life of the tunnel. On the basis of establishing the force model of the segments, by analyzing the force state of the segments, a theoretical calculation model of the segments floating is established. Taking the shield tunneling section ventilation shaft No.3-Caoqiao Station of Beijing Metro's New Airport Line as the engineering background, the abnormal rise of the segment was analyzed. By improving the performance of the synchronous grouting slurry, the floating amount of the tube segment was effectively controlled. And the slurry characteristics before and after the improvement were tested. Finally, based on the results of the slurry test and the theoretical calculation model, the floating volume of the tube segment was calculated. The results show that the theoretical calculation result of segment floating volume is consistent with the actual measured value. The theoretical calculation model in this paper has good accuracy. The segments float up a lot in a short time after it is released from the shield tail. Shortening the setting time of the slurry and improving its early strength are effective measures to control the floatation of the segments.
Current status and development trend of deep hole bench blasting technology in open-pit mines
Li Shenglin, Liang Shufeng, Li Chen, Liu Dianshu
2021, 6(5): 598-605.   doi: 10.19606/j.cnki.jmst.2021.05.009
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With the advancement of the information revolution, the promotion of resource development and environmental protection concepts in recent years, deep-hole bench blasting technology in domestic open-pit mines is developing rapidly under the guidance of intelligent and green blasting mining concepts. In terms of blasting equipment, a large number of electronic detonators were widely used; In terms of blasting systems, the intelligent blasting technology integrating intelligent drilling rig system, intelligent design system, explosive on-site mixing, and other technologies had taken shape. In terms of blasting technology, blasting vibration prediction theory and control, dust control, and shock wave and noise prevention, etc. have effectively controlled of the harmful effects of blasting, and gradually achieved the requirements of green blasting. Lastly, the problems in blasting equipment and blasting technology were sorted out, and the future development and research directions of green intelligent blasting in open-pit mines were pointed out.
Time-dependent stability analysis of open-pit slope considering life-cycle
Bao Min, Chen Zhonghui, Wang Xiong, Yang Jihai, Shen Zuodong
2021, 6(5): 606-614.   doi: 10.19606/j.cnki.jmst.2021.05.010
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Based on the influence of excavation and creep degradation on the stability of high slopes in open-pit, a stability model of slopes in life-cycle is proposed. By introducing the deterioration theory of rock strength, the calculation formula of safety factor under time effect is derived. Considering the prestress loss of anchor cable and the creep phenomenon of slope, the expression of safety factor of creep slope under prestress loss condition is established. Forthemore, the influence law of time factor of slope and prestress loss of anchor cable on slope is discussed. Taking Dagushan Xijing slope as an example, the decay theory is embedded into the strength reduction method with the help of the flash language built in the FLAC3D, and the improved strength reduction method is used to calculate the time-dependent safety factor of the slope. The results show that the "L" shaped deterioration of rock strength over time makes the factor of safety for creeping slopes lower than for excavation only, which is more consistent with the actual engineering. The reinforced slope still has the risk of instability due to the prestress loss of anchor cable. Four kinds of reinforcement control schemes of anchor cable are compared and selected, on the premise of meeting the safety production in the whole life cycle, the scheme with the best economic benefit is obtained.
On the theoretical calculation of tortuosity in porous media and its experimental validation
Xue Dongjie, Zhao Aibo, Liu Kuichang, Hou Mengdong, Fu Yanyan, Xin Cui, Xu Yanzhuo
2021, 6(5): 615-622.   doi: 10.19606/j.cnki.jmst.2021.05.011
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The quantitative characterization of connectivity of pore geometry and its reconstruction of topological connectivity are two important methods to describe the laws of fluid seepage in porous media.However, the lag of theoretical work severely restricts the emergence of new geometric modeling methods.The tortuosity is one of the key carriers connecting permeability and geometric structure, and its theoretical model has not been broken through.First, combining the Hagen-Poiseuille equation and Darcy formulas, the universal expression of the tortuosity for capillary model and the pore model composed by the particles are derived.Then for the low permeability medium, combined with the formula of capillary pressure, the tortuosity expression correlated to the saturation is obtained.Furthermore, the fractal dimension of tortuosity is introduced to explain the new term of fractal coefficient based on experimental analysis.Considering the bifurcated capillary channel, a bifurcation model was established to analyze the tortuosity characteristics and the geometric relationship between the mother and sub-holes based on the energy optimization criterion was obtained.Taking the salt rock as an example, the applicability and reliability of the theoretical formula of tortuosity are verified, and the research results provide a new idea for calculating the tortuosity of porous media.
Calculation of multi-fractal dimension of coal measure sedimentary rock and analysis of influencing factors
Zhang Na, Xun Xingjian, Wang Shuaidong, Zhang Haoyu
2021, 6(5): 623-632.   doi: 10.19606/j.cnki.jmst.2021.05.012
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In order to characterize the pore structure and fractal characteristics of coal-measure sedimentary rocks, three types of typical sedimentary rocks of the Middle Jurassic shale, mudstone and sandstone were selected as the research objects. Through X-ray diffraction(XRD)analysis and nuclear magnetic resonance(NMR)experiment, the correlation between NMR fractal dimension, mineral composition and physical property parameters was discussed by using fractal theory. The results are as follows: ① Based on the relaxation time cut-off value T2C, the NMR fractal dimension of shale and mudstone can be divided into the fractal dimension of adsorption pore DA(T2 ≤3 ms)and the fractal dimension of seepage pore DS (T2 >3 ms). ② In terms of reservoir physical properties, NMR fractal dimension Df has a good linear negative correlation with porosity, permeability, and reservoir quality index, indicating that NMR fractal dimension can be used as an important indicator of rock physical properties. ③ In terms of mineral composition, the content of quartz and feldspar has a weak negative correlation with the fractal dimension Df, and clay minerals have different influences on the fractal dimension due to multiple factors such as sedimentary environment, physical and chemical properties and mineral content.
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Experimental study on the extraction of niobium from crude niobium ore by KOH hydrothermal
Wang Weidong, Li Zhao, Wang Xiaohui, Zheng Shili
2017, 2(1): 75-81.  
[Abstract](632) [PDF 6699KB](17)
Abstract:
Because the crude niobium ore is difficult to be used,according to the composition analysis and phase analysis of crude niobium ore,the KOH hydrothermal method was used to research the dissolution of crude niobium ore and the dissolution of crude niobium under hydrothermal system was researched by changing the temperature and the KOH concentration.The results show that the dissolution of niobium from crude niobium ore could reach 90%,at 30% of KOH concentration,and 200℃;the dissolution of niobium increased first and then decreased with the increasings of KOH concentration and temperature;in the whole process of the dissolution,the alkaline components Fe,Mn,Mg kept a low dissolution yields.XRD and SEM’s results show that the increasings of KOH concentration and temperature accelerated the decomposition of (Fe,Mn)(Nb,Ta)2O6.When the KOH concentration was 30%,and the temperature was 200℃,continuing to strengthen the reaction conditions,the dissolution of Nb decreased significantly owing to the transformation from soluble K8Nb6O19 to insoluble KNbO3.
Mineral resources evaluation model research based on BP neural network and TSVM algorithm
Zhao Xuejun, Li Yuzhen, Wu Wenbin
2016, 1(2): 188-195.  
[Abstract](539) [PDF 4159KB](18)
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In the study of mineral resources evaluation model, the problem that the number of positive samples must be specified in the TSVM in the unlabeled samples. Then this article applied the improved algorithm to the evaluation of mineral resources, and the algorithm is TSVM based on BP neural network and BP-TSVM for short. The SVM is applied to studying the discernment and classification of labeling samples. We will annotate the plus or minus of unlabeled data within the boundary of already classified by utilizing BP neural network. The labeling samples as learned by SVM in the next iteration. The new algorithm will avoid decreased classified ability. TSVM can have more accurate estimates of number of plus of labeled data. Also, the number of training samples can reduce training times. The experimental result proves that compared with conventional SVM,TSVM and BP neural network the BP-TSVM is more accurate in evaluation of mineral resources.

Sponsored by: China University of Mining and Technology (Beijing)

Competent unit: Ministry of Education, People's Republic of China

Publisher: Emergency Management Press

Eidtor-in-chief: Suping Peng

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ISSN2096-2193

CN10-1417/TD

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