Numerical simulation on tendency mining fracture evolution characteristics of overlying strata and coal seams above working face with large inclination angle and mining depth

The movement of the overlying strata in steeply dipping coal seams is complex, and the deformation of roof rock beam is obvious. In general, the backfill mining method can improve the stability of the surrounding rock effectively. In this study, the 645 working face of the tested mine is used as a prototype to establish the mechanical model of the inclined roof beam using the sloping flexible shield support backfilling method in a steeply dipping coal seam, and the deflection equation is derived to obtain the roof damage structure and the maximum deflection position of the roof beam. Finally, numerical simulation and physical similarity simulation experiments are carried out to study the stability of the surrounding rock structure under backfilling mining in steeply dipping coal seams. The results show the following: (1) With the support of the gangue filling body, the inclined roof beam has smaller roof subsidence, and the maximum deflection position moves to the upper part of working face. (2) With the increase of the stope height, the stress and displacement field of the surrounding rock using the backfilling method show an asymmetrical distribution, the movement, deformation, and failure increase slowly, and the increase of the strain is relatively stable. Compared with the caving method, the range and degree of the surrounding rock disturbed by the mining stress are lower. The results of numerical simulation and physical similarity simulation experiment are generally consistent with the theoretically derived results. Overall, this study can provide theoretical basis for the safe and efficient production of steeply dipping coal seams.

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A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

Advances in Civil Engineering ◽

10.1155/2018/8161498 ◽

2018 ◽

Vol 2018 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Jie Fang ◽

Lei Tian ◽

Yanyan Cai ◽

Zhiguo Cao ◽

Jinhao Wen ◽

...

Keyword(s):

Numerical Simulation ◽

Coal Seam ◽

Coal Mining ◽

Water Inrush ◽

Mining Area ◽

Analysis Model ◽

Fractured Zones ◽

Working Face ◽

Seam Mining ◽

Overlying Strata

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

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Study on Surrounding Rock Structure Evolution Characteristics and Roof Control Techniques of the Retained Roadway Formed by Roof Cutting in Inclined Coal Seams

Shock and Vibration ◽

10.1155/2021/7491887 ◽

2021 ◽

Vol 2021 ◽

pp. 1-20

Author(s):

Guangyuan Yu ◽

Jiong Wang ◽

Jianjun Ren ◽

Jinzhu Hu ◽

Zhifu Pan ◽

...

Keyword(s):

Structure Evolution ◽

Coal Seams ◽

Supporting System ◽

Working Face ◽

Evolution Characteristics ◽

Rock Structure ◽

Support Resistance ◽

Pillar Mining ◽

Three Stages ◽

Constant Support

To control the roof during gob-side entry retaining by roof cutting in inclined coal seams, the retained gob-side roadway is zoned based on the mechanical principle and technological process of no-pillar mining with gob-entry retention. A simplified mechanical model for surrounding rocks in different subzones was established by using theoretical analysis and numerical simulation to attain the demand for the support resistance and deformation of the roof in different subzones. According to load and deformation characteristics of the roof and mechanical characteristics of NPR cables, single props, and a sliding-type gangue-retaining structure formed by U-shaped steel inserts, the supporting systems for roadways in different subzones and the constitutive model thereof were established. On this basis, the action of the supporting system was analysed and a field test was performed. The results show that the supporting system undergoes three stages of behaviour, i.e., pressure growth, yielding under constant pressure, and stabilisation during whole entry retention. It can guarantee the collaborative deformation of the supporting systems with the roof on the premise of constant support resistance, thus satisfying the requirement for roadway protection. The roadway 150 m back from the working face is stable, and the final convergence between the roof and floor of the retained entry is 257 mm, showing a favourable entry-retention effect.

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Novel Application of the Roof-Cutting-Type Gob-Side Entry Retaining in Coal Mine

Mathematical Problems in Engineering ◽

10.1155/2021/1625282 ◽

2021 ◽

Vol 2021 ◽

pp. 1-16

Author(s):

Jiong Wang ◽

Wenfei Li ◽

Daoyong Zhu ◽

Weili Gong ◽

Yi Su

Keyword(s):

Stable State ◽

Stress Evolution ◽

Coal Seams ◽

Working Face ◽

Mining Conditions ◽

Support Resistance ◽

Stress And Deformation ◽

Cutting Height ◽

Roof Deformation ◽

Overlying Strata

In this study, the roof-cutting-type gob-side entry retaining is introduced, and its application in medium-thickness coal seams is studied. Based on the analysis of the construction procedure and principle, the mechanical model of the retained roadway structure and cantilever beam formed by roof cutting was established, and the support resistance and roof deformation were obtained. In addition, through technological design analysis and numerical simulation, the parameters of roof cutting were determined. The roof-cutting height and angle were designed to be 9 m and 15°, respectively. Flac3 D was used to analyze the stress evolution law under different mining conditions. The stress on the integrated coal side and roof subsidence was lower when the roof-cutting height was 8∼10 m and the cutting angle was 15°. Through field monitoring, the roof pressure, gob-side lateral gangue retaining pressure, anchor cable stress, and deformation of the surrounding rock eventually reached a stable state. This indicates that the roof cutting can effectively cut down the overlying strata over the gob and form a stable entry structure to meet the requirements of the next working face.

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The Influences of Key Strata Compound Breakage on the Overlying Strata Movement and Strata Pressure Behavior in Fully Mechanized Caving Mining of Shallow and Extremely Thick Seams: A Case Study

Advances in Civil Engineering ◽

10.1155/2019/5929635 ◽

2019 ◽

Vol 2019 ◽

pp. 1-11 ◽

Cited By ~ 6

Author(s):

Junmeng Li ◽

Yanli Huang ◽

Jixiong Zhang ◽

Meng Li ◽

Ming Qiao ◽

...

Keyword(s):

Numerical Simulation ◽

Abutment Pressure ◽

Simulation Software ◽

Strata Movement ◽

Key Strata ◽

Pressure Behavior ◽

Ground Pressure ◽

Working Face ◽

Overlying Strata Movement ◽

Overlying Strata

In order to analyze the impact of compound breakage of key strata on overlying strata movement and strata pressure behavior during the fully mechanized caving mining in shallow and extremely thick seams, this paper took the 1322 fully mechanized caving face in Jindi Coal Mine in Xing County as the engineering background. Under the special mining and geological condition mentioned above, UDEC numerical simulation software was applied to research the engineering problems, and results of numerical simulation were verified through the in-site measurement. The research results showed that during the fully mechanized caving mining in shallow and extremely thick seams, the inferior key strata affected by mining movement behaved in the mode of sliding instability and could not form the stable structure of the voussoir beam after breaking and caving. In addition, the main key strata behaved in the mode of rotary instability, and the caving rocks behind the goaf were gradually compacted because of the periodic instability of the main key strata. With the continuous advance of the working face, the abutment pressure of the working face was affected by the compound breakage and periodic instability of both the inferior key strata and the main key strata, and the peaks of the abutment pressure presented small-big-small-big periodical change characteristics. Meanwhile, the risk of rib spalling ahead of the working face presented different levels of acute or slowing trends. The actual measurement results of ground pressure in the working face showed that, in the working process, the first weighting interval of the inferior key strata was about 51 m and its average periodic weighting interval was about 12.6 m, both of which were basically consistent with the results of numerical simulation. The research has great significance in providing theoretical guidance and practical experience for predicting and controlling the ground pressure under the similar mining and geological conditions.

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Similar Physical Modeling of Roof Stress and Subsidence in Room and Pillar Mining of a Gently Inclined Medium-Thick Phosphate Rock

Advances in Civil Engineering ◽

10.1155/2021/6686981 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Xiaoshuang Li ◽

Zhifang Liu ◽

Shun Yang

Keyword(s):

Phosphate Rock ◽

Yunnan Province ◽

Room And Pillar Mining ◽

Working Face ◽

Evolution Characteristics ◽

Failure Evolution ◽

Phosphate Mine ◽

Pillar Mining ◽

Maximum Subsidence ◽

Overlying Strata

Gently inclined medium-thick orebodies are generally recognized as the most difficult type of orebody to mine, using current available strategies (i.e., the room and pillar method). In the present study, a similar physical model was used to investigate the roof stress and subsidence for mining gently inclined medium-thick phosphate rock from the Jinning Phosphate Mine, Yunnan Province, China. The stress field, displacement field, and roof failure evolution characteristics of the surrounding rock with stope structures of 3 m, 5 m, or 8 m ore pillars were considered. The results showed that, after mining stopped, obvious pressure relief areas formed above the three stope structures, and pressure-bearing areas formed at the front of the roof. With extending the mining in the working face, the stress relief boundary also gradually increased, and the top of the roof tended to sink with a maximum subsidence of –14.58 mm, –4.67 mm, and –3.48 mm. Due to the mining activity, the overlying strata bent and subsided from top to bottom, creating bending subsidence, fracture, and caving zones.

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The Law of Fracture Evolution of Overlying Strata and Gas Emission in Goaf under the Influence of Mining

Geofluids ◽

10.1155/2021/2752582 ◽

2021 ◽

Vol 2021 ◽

pp. 1-16

Author(s):

Cheng Cheng ◽

Xiaoyu Cheng ◽

Rui Yu ◽

Wenping Yue ◽

Chao Liu

Keyword(s):

Maximum Height ◽

Gas Migration ◽

Gas Emission ◽

Pressure Relief ◽

Gas Concentration ◽

Fracture Evolution ◽

Working Face ◽

Simulation Results ◽

The Law ◽

Overlying Strata

Mining is associated with poor safety due to pressure relief gas emission from the goaf during the production period. The aim of this study was to explore a case study of the Wangjialing coal mine 12322 working face in Shanxi, China, through physical simulation and field observation. The mine is characterized by overlying strata fracture in goaf during the process of working face mining. A mathematical model of gas source emission from the working face and gas migration and the finite element COMSOL software were used to simulate the law of gas migration in the region with overlying strata fissures under the influence of mining. The simulation results were used to explore the law of distribution of pressure relief gas in goaf. Rational parameters of the high-level directional long borehole for the pressure relief gas extraction in goaf were designed based on experimental results. The results showed that the development of the region with overlying strata fissures is affected by mining. In addition, the “trapezoid platform structure” is formed after fracture areas are connected. The maximum height of the stope caving zone was between 26.8 m and 28.1 m, and the maximum height of the fracture zone was approximately 110 m. The gas concentration exhibited a saddle-shaped distribution on the cut surface of the direction of the strike. Furthermore, the gas concentration showed an overall upward trend from the intake airflow roadway to the return airflow roadway and gradually decreased after reaching the maximum. In the vertical direction, gas concentration increased with the increase in the layer, and the position of the highest point of gas concentration gradually shifted to the direction of the intake airflow roadway. Construction parameters of the high directional long borehole were designed through simulation results. After steady extraction and stable extraction, the maximum gas concentration in the upper corner of the working face was 0.49%, and the maximum gas concentration in return airflow was 0.34%. The findings of this study provide information on the law of fracture evolution of overlying strata and gas migration in goaf under the influence of mining. These findings provide a basis for reducing gas overlimit in the working face or return airway corner, thus improving the safety production capacity of the coal mine.

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Study on Rules of Fault Stress Variation Based on Microseismic Monitoring and Numerical Simulation at the Working Face in the Dongjiahe Coal Mine

Shock and Vibration ◽

10.1155/2019/7042934 ◽

2019 ◽

Vol 2019 ◽

pp. 1-12 ◽

Cited By ~ 1

Author(s):

Ke Ma ◽

Fuzhen Yuan ◽

Duanyang Zhuang ◽

Quansheng Li ◽

Zhenwei Wang

Keyword(s):

Numerical Simulation ◽

Rock Mass ◽

Coal Mine ◽

Maximum Principal Stress ◽

Microseismic Monitoring ◽

Stress Variation ◽

Fault Activation ◽

Working Face ◽

Damage Theory ◽

Overlying Strata

Microseismic monitoring technology was used to study the real-time evolution of rock mass damage generated by a working face as it approached a fault in Dongjiahe Coal Mine. The influence of vertical zoning of overlying strata on damage at the fault was analyzed. Numerical simulation using finite element method based on meso-statistical damage theory was used to investigate the nonlinear and nonuniform failure behaviour of the rock mass near the fault. The response of the fault stress to excavation activity and the rule of fault activation were examined. The results show that the fault damage has segmental characteristics. Microcracks are first generated at the fractured zone that is divided into lower, middle, and upper sections, located 30∼70 m, 120∼180 m, and 230∼280 m above the coal seam, respectively. There was also a segmentation phenomenon in the stress response of fault. The risk of fault activation was evaluated by using the ratio of shear stress to the maximum principal stress. When the working face was 260 m and 140 m away from the fault, the activation risk at the upper-middle and lower sections began to increase, respectively. When the fault was within 60 m, the risk of fault activation was highest.

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Research on the First Breaking Mechanism of the Main Roof of Coal Seam with High Dip Angle

Advances in Civil Engineering ◽

10.1155/2020/8820625 ◽

2020 ◽

Vol 2020 ◽

pp. 1-8

Author(s):

Xinyu Hu ◽

Jinlong Cai

Keyword(s):

Numerical Simulation ◽

Mechanical Model ◽

Main Roof ◽

Distribution Characteristics ◽

Coal Seams ◽

Working Face ◽

Elastic Thin Plate ◽

Breaking Mechanism ◽

Dip Angle ◽

Clamped Edges

In order to study the mechanism and characteristics of the first breaking of the roof in thick coal seams with high dip angles, a mechanical model of elastic thin plate with four clamped edges of the roof was established, and the expressions of the deflection and stress of the roof were obtained by the energy method. The influence of the change in seam dip angle on the first breaking distance of the roof was presented. Based on the stress solution, the roof breaking criterion was proposed, and the breaking distance of the roof was calculated. Combined with numerical simulation, the stress distribution characteristics of the upper and lower surfaces of the stope roof were analyzed. The results show that the first breaking distance of the roof is inversely proportional to the seam dip angle. Broken morphology of roof in high dip seam is different from the “O-X” morphology of horizontal roof. The roof breaking order of the seam with high dip angle is middle-middle upper-middle lower-upper-lower. These research results have certain theoretical guiding significance for the study of the first breaking mechanism of the main roof of highly inclined working face of coal seams.

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Study on the Process Optimization of Fully-Mechanized Hard Top-Coal Caving with Large Inclination Angle

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.889-890.234 ◽

2014 ◽

Vol 889-890 ◽

pp. 234-240

Author(s):

Yong Zhang ◽

Jin Kai Liu ◽

Qi Li ◽

Jian Jian Zhao ◽

Yue Ma

Keyword(s):

Numerical Simulation ◽

Field Test ◽

Inclination Angle ◽

Recovery Rate ◽

Element Model ◽

Simulation Software ◽

Industrial Experiment ◽

Working Face ◽

Geological Conditions ◽

Technological Achievement

In order to solve the problem of low recovery rate of top-coal during fully-mechanized coal caving with large inclination angle, the optimization of fully-mechanized hard top-coal caving with large inclination angle is studied in this paper respectively in the two aspects of changing caving characteristics of top-coal and caving process. By adopting the method of top-coal pre-blasting to weaken top-coal, the caving characteristics is effectively improved which creates conditions for the successful caving of top-coal; meanwhile, the statistical result of recovery rate of top-coal is obtained by using numerical simulation software PFC2D based on particle element model, it is found that coal loss during top-coal caving and the loss at the ends of working face is effectively reduced when 2 cuttings and 1 caving method with multi-round spaced drawing is taken, which significantly improved the recovery rate of top-coal and it has passed the field test of industrial experiment. This technological achievement could provide some reference to the fully mechanized working face in this coal mine or working faces under similar geological conditions.

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