Mechanism and Evolution Control of Wide Coal Pillar Bursts in Multithick Key Strata

Coal mine pillar burst frequently occurs in Western China, which seriously restricts safe production. This paper takes the 35 m coal pillar of the 3102 working face of MKQ coal mine as the engineering background. The mechanism and evolution control of pillar bursts in multithick key strata are studied using field investigation, theoretical analysis, and numerical simulation. The mechanism of dynamic and static stress-induced pillar bursts was revealed combining the “O-X” broken features for key strata and numerical simulation of pillar stress evolution. A prevention scheme is put forward for strata presplit blasting and adjusting coal pillar width to minimize the dynamic and static stresses. The results demonstrate the following. (1) In the multithick strata, the first and second near-field subkey strata have perpendicular “O-X” broken features, whereas the third far-field subkey has parallel “O-X” broken features. The working face has three kinds of periodic weighting phenomena: long, medium, and short. (2) The simulated vertical stress curve of 35 m coal pillar goes through three states: two-peak, asymmetric trapezoidal and symmetrical trapezoidal shape with the different advancing position of working face. The stress concentration is extensively promoting a high-risk area for rock burst. (3) The coal pillar burst was induced by the superposition of energy released by the key strata breaking and the elastic energy accumulated in the wide coal pillar. (4) The monitoring data showed that the long, medium, and short periodic weighting steps of multithick key strata are 141.6 m, 43.2–49.6 m, and 17.6–27.2 m, respectively. The microseismic events energy, frequency, and stress of hydraulic support increment are the highest during the long periodic weighting, and the spatial distribution of microseismic events coincides with the stress concentration area. The theoretical analysis is confirmed with the field practice.

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Study on the Mechanism and Control of Rock Burst of Coal Pillar under Complex Conditions

Geofluids ◽

10.1155/2020/8847003 ◽

2020 ◽

Vol 2020 ◽

pp. 1-19

Author(s):

Xingping Lai ◽

Huicong Xu ◽

Jingdao Fan ◽

Zeyang Wang ◽

Zhenguo Yan ◽

...

Keyword(s):

Stress Concentration ◽

Rock Burst ◽

Coal Mine ◽

High Stress ◽

Coal Pillar ◽

Vertical Stress ◽

Body Area ◽

High Stress Concentration ◽

Solid Coal ◽

Working Face

In order to explore the mechanism of coal pillar rock burst in the overlying coal body area, taking W1123 working face of Kuangou Coal Mine as the engineering background, the full mining stage of W1123 is simulated by FLAC3D. It is found that the high stress concentration area has appeared on both sides of the coal pillar when W1123 does not start mining. With the advance of the working face, the high stress concentration area forms X-shaped overlap. There is an obvious difference in the stress state between the coal pillar under the solid coal and the coal pillar under the gob in W1123. The concrete manifestation is that the vertical stress of the coal pillar below the solid coal is greater than the vertical stress of the coal pillar below the gob. The position of the obvious increase of the stress of the coal pillar in the lower part of the solid coal is ahead of the advancing position of the working face, and the position of the obvious increase of the stress of the lower coal pillar in the gob lags behind the advancing position of the working face. At the same time, in order to accurately reflect the true stress environment of coal pillars, the author conducted a physical similarity simulation experiment in the laboratory to study the local mining process of the W1123 working face, and it is found that under the condition of extremely thick and hard roof, the roof will be formed in the gob, the mechanical model of roof hinged structurer is constructed and analyzed, and the results show that the horizontal thrust of roof structure increases with the increase of rotation angle. With the development of mining activities, the self-stable state of the high stress balance in the coal pillar is easily broken by the impact energy formed by the sudden collapse of the key strata. Therefore, the rock burst of coal pillar in the overlying coal body area is the result of both static load and dynamic load. In view of the actual situation of the Kuangou Coal Mine, the treatment measures of rock burst are put forward from the point of view of the coal body and rock mass.

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Study on Numerical Simulation of Fully Mechanized Top Coal’s Caving Property of Tang Gong Ta Coal Mine

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1094.410 ◽

2015 ◽

Vol 1094 ◽

pp. 410-414

Author(s):

Quan Ming Liu

Keyword(s):

Numerical Simulation ◽

Stress Concentration ◽

Coal Mine ◽

Peak Stress ◽

Simulation Method ◽

Numerical Simulation Method ◽

Working Face ◽

Coal Wall

Using numerical simulation method,fully mechanized top coal’s caving property of Tang gong ta coal mine was studied.The results show at primary mining period of fully mechanized working face, there were stress concentration regions at the front and rear of coal wall,but it was not distinct in the front and top coal’s caving property was not ideal.When it advanced to 84m of the working face,there would be obvious peak stress at the front and rear of coal wall. It accelerated top coal’s caving.When it advanced to 140m of the working face,top coal was caved with coal mining.Finally it was proved on the scene. The results of the study in fully mechanized mining’s safety and efficiency has some guiding role.

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Optimization Coal Pillar Size of Top Coal Caving Face with Dynamic Pressure Impact

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.675-677.1395 ◽

2014 ◽

Vol 675-677 ◽

pp. 1395-1400 ◽

Cited By ~ 1

Author(s):

Wen Zhou Li

Keyword(s):

Numerical Simulation ◽

Coal Mine ◽

Simulation Analysis ◽

Dynamic Pressure ◽

Coal Pillar ◽

Large Error ◽

Working Face ◽

Pressure Impact ◽

Mine Depth ◽

Pillar Size

AH Wilson coal pillar was used widely as it’s simply, but it’s appeared large error for field implementation as its difference assume conditions, mine depth H and mine thickness m. AH Wilson coal pillar formula was studied precisely by in-site stresses test and numerical simulation analysis for N3-5 top coal caving working face of CHANGCUN coal mine in Lu’an coal district of China, then modified AH Wilson formula was put forward as L = 0.008mH + 8.4,then the precise coal pillar size 18m was used in filed implementation, filed testing proved coal pillar size was reasonable.

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Study on the Pressure-Bearing Law of Backfilling Material Based on Three-Stage Strip Backfilling Mining

Energies ◽

10.3390/en13010211 ◽

2020 ◽

Vol 13 (1) ◽

pp. 211 ◽

Cited By ~ 1

Author(s):

Xiaoping Shao ◽

Xin Li ◽

Long Wang ◽

Zhiyu Fang ◽

Bingchao Zhao ◽

...

Keyword(s):

Numerical Simulation ◽

Thin Plate ◽

Coal Mine ◽

Physical Simulation ◽

Plate Theory ◽

Coal Pillar ◽

Smooth Transition ◽

Main Bearing ◽

Working Face ◽

Rock Load

During strip backfilling mining in coal mines, the backfilling material is the main support structure. Therefore, studying the pressure law of the backfilling material is essential for the safe and efficient mining of coal resources. Based on research into strip backfilling mining at working face number 3216 of the Shanghe Coal Mine, and to smooth transition of overlying strata loads to the backfilling material, this study proposes a three-stage strip backfilling mining method. Based on thin-plate theory, an elastic thin-plate model, a reasonable spacing of strip mining is constructed, and the reasonable mining parameters of “mining 7 m to retain 8 m” at working face number 3216 of the Shanghe Coal Mine are determined. The law of backfilling pressure in three-stage strip backfilling mining is studied through numerical simulation and physical simulation experiments. The results show that field measurement results are basically consistent with the experimental results and numerical simulation results. When three-stage strip backfilling mining is adopted, the stage-one backfilling material is the main bearing body to which the overlying rock load transfers smoothly and gradually, and the structure of the “overburden-coal pillar (or backfilling strip)” in the stope remains stable. In three-stage strip backfilling mining, the overlying rock load is ultimately transferred to the stage-one backfilling material, the stage-two backfilling material is the auxiliary bearing body, and the stage-three backfilling material mainly provides long-term stable lateral support for the stage-one backfilling material.

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Deformation Rules for Surrounding Rock in Directional Weakening of End Roofs of Thin Bedrocks and Ultrathick Seams

Advances in Civil Engineering ◽

10.1155/2020/8882374 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Fei Liu ◽

Zhanguo Ma ◽

Yongsheng Han ◽

Zhimin Huang

Keyword(s):

Abutment Pressure ◽

Main Roof ◽

Stability Control ◽

Surrounding Rock ◽

Western China ◽

Resource Exploitation ◽

Failure Characteristics ◽

Key Strata ◽

Working Face ◽

Geological Conditions

With the deployment of China’s energy strategy in the western regions, complex geological mining conditions such as thin bedrock and ultrathick seams in western China have caused a series of problems such as serious deformation of the surrounding rock at the ends of the working face and the increase in the lead abutment pressure of the roadways; the research on end roof deformation in the resource exploitation in western China has become one of the great demands of the industry. Based on the failure characteristics of rock mass, relying on the actual mining geological conditions of a coal mine in Inner Mongolia, the failure characteristics of the overlying rock strata under the influence of mining were simulated and analyzed using similar material simulation experiment, which intuitively reproduced the failure and deformation processes of the immediate roof, main roof, and key strata and revealed the mechanical mechanism of the directional weakening of the end roof. It is of great significance for the stability control of the surrounding rock at the end of the fully mechanized caving face in the thin bedrocks and ultrathick seams, reducing the abutment pressure of gate roadway and controlling the spontaneous combustion of residual coal in the goaf.

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Movement Law and Discriminant Method of Key Strata Breakage Based on Microseismic Monitoring

Shock and Vibration ◽

10.1155/2019/8652894 ◽

2019 ◽

Vol 2019 ◽

pp. 1-19 ◽

Cited By ~ 1

Author(s):

Yang Li ◽

Tianhong Yang ◽

Weidong Song ◽

Ling Yu

Keyword(s):

High Intensity ◽

Microseismic Monitoring ◽

Geological Structure ◽

Western China ◽

Dynamic Monitoring ◽

Ecological Environment ◽

Environmental Damage ◽

Key Strata ◽

Key Stratum ◽

Working Face

Because of the unique natural geography, geological structure, and ecological environment, there are serious geological disasters and environmental damage caused by the high-intensity mining in Western China. It seriously restricts the development of coal resources and the protection of ecological environment. In order to fully capture the law of key stratum breakage with high-intensity mining, the IMS microseismic system was introduced into Xiaojihan coal mine which is a typical high-intensity mining mine in Western China, and the whole process dynamic monitoring was carried out. The process of key stratum breakage was analysed by MS data, which were in agreement with the pressure analysis results of the hydraulic support of the working face. The results showed that there were the obvious forewarning characteristics in microseismic event number, energy release, energy index, Schmidt number, coefficient of seismic response, and b value when the key stratum was breaking. Then, a method to discriminate the breakage of key stratum was proposed by using the forewarning characteristics, which could provide the guidance for prevention and control of geological hazards in the working face with high-intensity mining.

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Deviatoric Stress Evolution Laws and Control in Surrounding Rock of Soft Coal and Soft Roof Roadway under Intense Mining Conditions

Advances in Materials Science and Engineering ◽

10.1155/2020/5036092 ◽

2020 ◽

Vol 2020 ◽

pp. 1-18

Author(s):

Dongdong Chen ◽

Chunwei Ji ◽

Shengrong Xie ◽

En Wang ◽

Fulian He ◽

...

Keyword(s):

Numerical Simulation ◽

Plastic Zone ◽

Theoretical Calculations ◽

Coal Pillar ◽

Surrounding Rock ◽

Deviatoric Stress ◽

Anchor Cable ◽

Soft Coal ◽

Working Face ◽

Failure Line

Aiming at the problem of large deformation and instability failure and its control of soft coal and soft roof roadway under intense mining, laboratory experiments, theoretical calculations, Flac3D numerical simulation, borehole peeping, and pressure observation were used to study the deflection characteristics of the deviatoric stress of the gas tailgate and the distribution and failure characteristics of the plastic zone in the mining face considering the strain softening characteristics of the roof and coal of roadway, and then the truss anchor cable-control technology is proposed. The results show the following: (1) The intense mining influence on the working face will deflect the peak deviatoric stress zone (PDSZ) of the surrounding rock of the gas tailgate. The influence distance of PDSZ is about 20 m in advance and 60 m in lag; the PDSZ at the gob side of the roadway is located in the range of 3–5.5 m from the surface of the coal pillar, while the coal wall side is mainly located in the range of 3–4.5 m at the shoulder corner and bottom corner of the solid coal. (2) The intense mining in the working face caused the nonuniform expansion of the surrounding rock plastic area of the gas tailgate. The two shoulder angles of the roadway and the bottom of the coal pillar have the largest damage range, and the maximum damage location is the side angle of the coal pillar (5 m). Angle and bottom angle of coal pillar are the key points of support control. (3) The plastic failure line of the surrounding rock of the gas tailgate is always between the inner and outer contours of the PDSZ, and the rock mass in the PDSZ is in a stable and unstable transition state, so the range of anchor cable support should be cross plastic failure line. (4) The theoretical calculations and numerical simulation results agree well with the drilling peep results. Based on the deflection law of the PDSZ and the expansion characteristics of the plastic zone, a truss anchor cable supporting system with integrated locking and large-scale support function is proposed to jointly control the roof and the two sides, which effectively solves the problem of weak surrounding rock roadway under severe mining deformation control problems realizing safety and efficient production in coal mines under intense mining.

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Support design of main retracement passage in fully mechanised coal mining face based on numerical simulation

Applied Mathematics and Nonlinear Sciences ◽

10.2478/amns.2021.1.00059 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Yalong Li ◽

Mohanad Ahmed Almalki ◽

Cheng Li

Keyword(s):

Numerical Simulation ◽

Coal Mine ◽

Surrounding Rock ◽

Control Measures ◽

Coal Face ◽

Support Design ◽

Working Face ◽

Surrounding Rock Control ◽

Mining Face ◽

Mining Pressure

Abstract For the comprehensive mechanised coal mining technology, the support design of the main withdrawal passage in the working face is an important link to achieve high yield and efficiency. Due to the impact of mining, the roof movement of the withdrawal passage is obvious, the displacement of the coal body will increase significantly, and it is easy to cause roof caving and serious lamination problems, and even lead to collapse accidents, which will affect the normal production of the mine. In this paper, the mining pressure development law of the main withdrawal passage support under the influence of dynamic pressure is designed, the most favourable roof failure form of the withdrawal passage is determined, and the action mechanism and applicable conditions of different mining pressure control measures are studied. The pressure appearance and stress distribution in the final mining stage of fully mechanised coal face are studied by numerical simulation. The deformation and failure characteristics and control measures of roof overburden in the last mining stage of fully mechanised coal face are analysed theoretically. Due to the fact that periodic pressure should be avoided as far as possible after the full-mechanised mining face is connected with the retracement passage, some auxiliary measures such as mining height control and forced roof blasting are put forward on this basis. The relative parameters of the main supporting forms are calculated. The main retracement of a fully mechanised working face in a coal mine channel is put forward to spread the surrounding rock grouting reinforcement, reinforcing roof, and help support and improve the bolt anchoring force, the main design retracement retracement channels in the channel near the return air along the trough for supporting reinforcing surrounding rock control optimisation measures, such as through the numerical simulation analysis, the optimisation measures for coal mine fully mechanised working face of surrounding rock is feasible. Numerical simulation results also show that the surrounding rock control of fully mechanised working face of coal mine design improvements, its main retreat channel under the roof subsidence, cribbing shrank significantly lower, and closer, to better control the deformation of surrounding rock, achieved significant effect, to ensure the safety of coal mine main retracement channel of fully mechanised working face support.

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Research on the Redistribution Law of Lateral Mining Stress and the Bearing Characteristics of Section Coal Pillar in Extra-Thick Fully Mechanized Top-Coal Caving Mining

Shock and Vibration ◽

10.1155/2021/4355977 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Qingwei Bu ◽

Min Tu ◽

Baojie Fu

Keyword(s):

Stress Concentration ◽

Bearing Capacity ◽

Load Condition ◽

Coal Pillar ◽

Critical Dimension ◽

The Self ◽

Working Face ◽

Mining Pressure ◽

Seam Mining ◽

Pillar Size

Due to the change of ground stress environment caused by underground coal mining, the intense lateral mining stress concentration is formed around the stope; so section coal pillar is generally set up to bear the mining pressure, but the different sizes of coal pillars have obvious influence on the bearing capacity of those pillars and the characteristics of mining pressure. Mastering the mechanism characteristics by which coal pillars bearing capacity and mining stress distribution is crucial to identify the reasonable coal pillar size and give full play to the bearing role of section coal pillar, given their importance for the safety and bearing stability of engineering rock mass in underground coal mining. Therefore, the bearing characteristics of section coal pillar and the redistribution of mining stress are achieved with a mechanical model analysis on the basis of the analysis of coal pillar bearing and mining influence characteristics. Moreover, applying the elastic-plastic mechanics theory revealed the mechanical equations of the effective bearing size of coal pillar and redistribution of mining stress in longwall face. Combined with the analysis of a specific engineering example, the research results are as follows. During a roadway excavation, the continuous mining stress transfer occurs “stress redistribution” and the mechanical failure of bearing coal pillar consists of lateral mining and roadway side failures. The bearing coal pillar has two critical dimensions (i.e., the critical dimension W e of the self-bearing stability coal pillar and the critical dimension W p of failure through the coal pillar). The mechanical state of the lateral mining stress redistribution and bearing coal pillar is divided into the three situations: ① when the width of coal pillar W < W p , only one stress concentration area exists, the bearing capacity of the coal pillar is invalid at this stage, and the lateral mining stress concentration transfers to the roadway solid coal side; ② when the width of the coal pillar W e ≥ W ≥ W p , two stress concentration areas appear at this stage, and the coal pillar is in the critical state of self-bearing stability; ③ when the width of the coal pillar W > W e , three stress concentration areas are present, and the coal pillar at this stage is in a self-bearing stable state. Among all these factors, only the size of coal pillar is completely controllable, so the aspects of safe bearing and reserved size design of coal pillar, after estimating the critical size of coal pillar, the coal pillar size design is carried out according to the mine pressure control needs of mining engineering, and the cohesion, internal friction angle, interlayer friction coefficient, and coal seam mining height are improved by artificial technology, so as to realize the resource safe and efficient mining of all kinds of coal seam mining conditions; in the calculation of wide coal pillar size, the advance mining stress concentration at the end of the self-working face should be taken as the mining load condition, and the reserved size meets the condition of W > W e , thereby ensuring the stable bearing of the wide coal pillar despite the advanced mining stress concentration during the self-working face mining; in the calculation of narrow coal pillar size, the lateral mining stress concentration before mining should be taken as the mining load condition and the reserved size meets the condition W < W p , thereby realizing the effective transfer of mining stress concentration to the roadway solid coal side.

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Analysis of Roof Deformation Mechanism and Control Measures with Roof Cutting and Pressure Releasing in Gob-Side Entry Retaining

Shock and Vibration ◽

10.1155/2021/6677407 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Bing-Jun Sun ◽

Xin-Zhu Hua ◽

Yan Zhang ◽

Jiadi Yin ◽

Kai He ◽

...

Keyword(s):

Numerical Simulation ◽

Coal Mine ◽

Surrounding Rock ◽

Cutting Angle ◽

Working Face ◽

Support Resistance ◽

Key Block ◽

Cutting Height ◽

Basic Roof ◽

Roof Support

The mechanical model of the basic roof fracture structure is established on the basis of key block theory to study the roof breaking mechanism of gob-side entry retaining under roof cutting and pressure relief, and the analytical formula of roof support resistance is derived when the key block of the basic roof is stable. The influence of roof cutting angle and cutting height on roof support resistance is also analyzed. Determining the cutting seam parameters of the retained roadway roof is necessary to identify the support resistance of the roadway roof due to the correlation between the roof cutting parameters and the support resistance. Taking the II 632 haulage drift of the Hengyuan coal mine as the engineering background, FLAC3D numerical simulation is used in this paper to analyze the influence of different roof cutting angles and cutting heights on the surrounding rock structure evolution of retained roadways. Results show that the roof cutting angle and cutting height respond to the support resistance of the retained roadway roof, and the support resistance required by the roof increases with the roof cutting angle and cutting height. This condition ensures that the side roof of the gob can be cut off smoothly, and the support resistance required by the roof of retained roadways is within a reasonable range. Through theoretical and numerical simulation analysis, the reasonable roof cutting height of II 632 haulage drift is 8 m and the roof cutting angle is 15°. The theoretical analysis and numerical simulation results reveal that the required support resistance to maintain the stability of the roadway roof is 0.38 MPa. The supporting scheme of the roof of the II 632 haulage drift in the Hengyuan coal mine is then designed. Finally, the field industrial test is used for verification. The borehole imaging results show that the overall line of the retained roadway roof is small based on the description of field monitoring results. The deformation of the surrounding rock surface of the retained roadway is less than 100 mm, and the roadway is 40 m from the lagging working face. The deformation rate of surrounding rock decreases with the increase in distance from the working face. The integrity of the retained roadway roof is good, and the deformation of the surrounding rock is effectively controlled.

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