Failure Mechanism of Gob-Side Roadway under Overlying Coal Pillar Multiseam Mining

Roadway deformation and rock burst are the two key challenges faced by the safe operation of coal mines. Aiming at the issue of large deformation of the gob-side roadway under coal pillars in multiseam mining, this study has considered the case of the 8308 panel of Xinzhouyao coal mine in China. Based upon a combination of theoretical analysis, numerical simulations, and engineering practices, the mechanical model of “stress and deformation quantitative calculation of gob-side roadway under overlying coal pillars” was established in this study. The analytical solutions of the vertical stress distribution and the plastic zone of the gob-side roadway under overlying coal pillars were obtained. Finally, the accuracy of the mechanical model was verified using numerical simulations. The results showed that the coal pillar, upright above the gob-side roadway, and the cantilever roof around the gob-side roadway were the main factors leading to stress concentration and deformation around the gob-side roadway. For the particular cases considered in this study, the peak stress of the gob-side roadway could reach 1.8 times of the self-weight stress of overlying strata. The rates of the contribution of the gob-side roadway’s overlying pillar and the cantilever roof around the gob-side roadway to peak stress were 78.3% and 16%, respectively. The obtained results have an essential reference significance for stress calculations and rock burst prevention design of gob-side roadway under overlying coal pillars in multiseam mining.

Download Full-text

Destabilization and energy characteristics of coal pillar in roadway driving along gob based on rockburst risk assessment

Royal Society Open Science ◽

10.1098/rsos.190094 ◽

2019 ◽

Vol 6 (7) ◽

pp. 190094 ◽

Cited By ~ 2

Author(s):

Yi Xue ◽

Zhengzheng Cao ◽

Wenlong Shen

Keyword(s):

Mathematical Model ◽

Mechanical System ◽

Rock Burst ◽

Research Result ◽

Coal Pillar ◽

Peak Stress ◽

Observation Data ◽

The Sustainable Development ◽

Coal Pillars ◽

Energy Accumulation And Dissipation

Roadway driving along adjacent goafs is an effective method to develop the recovery rate of coal resources. However, rock burst triggered by dynamic destabilization of coal pillars poses a serious threat to safe and efficient mining, thereby significantly restricting the sustainable development of coal mines. In this study, from the perspectives of energy accumulation and dissipation, a mathematical model of coal pillars is established and the energy equilibrium relationship of the mechanical system is analysed. The rock burst mechanism of coal pillars in gob-side entry is obtained based on a fold catastrophe mathematical model. Results indicate that the rock burst triggered by the instability is a destabilization phenomenon. If the stiffness factor of the mechanical system is less than 1 and the external force is enough to lead coal pillars to the peak stress point, then rock burst disaster occurs. The engineering analysis and numerical simulation are conducted to study the rock burst in the gob-side entry that occurred in Xin'an coal mine. Stress release caused by mining can reduce the risk of rock burst to a certain extent. The amount of elastic energy released is 6.4512 × 10 7 J, which is close to the observation data and verifies the correctness and rationality of the research method. The research result provides a theoretical basis and technical guidance for rock burst prevention and control in roadway driving along adjacent goafs.

Download Full-text

Mechanisms behind strong strata behaviour in high longwall mining face-ends under shallow covers

Journal of Geophysics and Engineering ◽

10.1093/jge/gxz027 ◽

2019 ◽

Vol 16 (3) ◽

pp. 559-570 ◽

Cited By ~ 4

Author(s):

Weibing Zhu ◽

Xiangrui Qi ◽

Jinfeng Ju ◽

Jingmin Xu

Keyword(s):

Longwall Mining ◽

Coal Pillar ◽

Field Measurements ◽

Main Roof ◽

Longwall Face ◽

Effective Control ◽

Coal Seams ◽

Roof Collapse ◽

Coal Pillars ◽

Roadway Deformation

Abstract Safe and efficient mining of shallow coal seams relies on the understanding and effective control of strata behaviour. Field measurements, theoretical analysis and numerical simulations are presented in this study to investigate the mechanism behind abnormal strata behaviour, such as roof collapse and severe roadway deformation, that occurs in high longwall face-ends under shallow cover. We observed that coal pillars with two sides being mined out become unstable when the cover depth exceeds a certain value. The instability of the coal pillar can alter the fracture line of the overlying strata, triggering a reversed rotation of the ‘curved triangle blocks’ that form after the breakage of the overlying main roof. The revolving blocks apply stress on the roof strata directly above the longwall face-end, resulting in roof collapse. The collapse of both the coal pillars and the roof also leads to the advancement and increase of the overlying abutment pressure, which further causes severe roadway deformation in front of the working face. The strong strata behaviour that occurs in high longwall face-ends with shallow cover is presented in this study and countermeasures are proposed, such as widening or strengthening the coal pillar, or implementing destress blasting. The countermeasures we proposed and the results of our analyses may facilitate the safe mining of shallow coal seams with similar problems in the future, and may improve the safety and efficient working of coal mines.

Download Full-text

Research on Failure Mechanism and Strengthening of Broken Roadway Affected by Upper Coal Pillar

Advances in Civil Engineering ◽

10.1155/2019/8132817 ◽

2019 ◽

Vol 2019 ◽

pp. 1-13 ◽

Cited By ~ 2

Author(s):

Fulian He ◽

Zheng Zheng ◽

Hengzhong Zhu ◽

Bo Yang

Keyword(s):

Stress Distribution ◽

Failure Mechanism ◽

Coal Pillar ◽

Control Area ◽

Surrounding Rock ◽

Horizontal Line ◽

Protective Function ◽

Working Face ◽

Coal Pillars ◽

Roadway Deformation

The principal stress difference is introduced as a new evaluation index in order to better understand the failure mechanism of roadways affected by upper coal pillars and characterize failure of rock mass. Compared with traditional methods, it facilitates quantitative analysis. Moreover, we combine the semiplane theory and we obtain the stress distribution on the coal pillar’s bedrock and the strengthening control area from the “change point” position along a 21 m horizontal line. The influence of multiple stresses induced from mining on a roadway is analyzed. It is found that rock failure is most likely while mining the 051606 working face, followed by mining the 051604 working face, and the stress influence on the upper pillar has the lowest failure probability. In addition, based on the asymmetry of the surrounding rock stress distribution, this study proposes strengthening control technology of surrounding rock on the basis of a highly stressed bolting support and anchor cable, adding to the steel ladder beam, steel mesh, and shed support’s protective function to the roadway’s roof and ribs. Finally, through field observations, it is concluded that the roadway deformation is within the controllable range.

Download Full-text

Research on Reasonable Width of Coal Pillars of Non-equal Width Isolated Working Face Heading Goaf in Deep Mine

10.21203/rs.3.rs-483480/v1 ◽

2021 ◽

Author(s):

weili yang ◽

Quande wei ◽

Zhonghui Wang ◽

Zhizeng Zhang ◽

Xiaocheng Qu ◽

...

Keyword(s):

Rock Burst ◽

Critical State ◽

Research Result ◽

High Stress ◽

Coal Pillar ◽

Stress Monitoring ◽

Equilibrium Relation ◽

Deep Mine ◽

Working Face ◽

Coal Pillars

Abstract Setting reasonable coal pillar is a key to ensure safe mining of island coal face heading goaf in deep mine. With determination of reasonable width of coal pillars of non-equal width isolated working face 3201 in worked-out area in one mine in Shandong as the engineering background, a research was conducted on the mechanism of rock burst induced by and the reasonable width of coal pillars of isolated working face in worked-out area and the main conclusions are as follows: (1) the coal pillars of isolated working face 3201 in worked-out area changed from pillars with goaf on two sides→pillars with goaf on three sides→pillars with goaf on four sides, resulting in evolution of overlying strata from pre-mining static “┒-shaped” structure→“C-shaped” structure→“O-shaped” structure and corresponding spatial stress from “saddle-shaped” profile→“platform-shaped” profile→“arch-shaped” profile; (2) the rock burst was induced by coal pillars, because the high stress on coal pillars at critical state of a rock burst was greater than their comprehensive strength and induced a rock burst due to sudden instability; (3) by establishing a bearing and load model of coal pillars at critical state of a rock burst and based on the equilibrium relation, an method for estimating reasonable width of coal pillars of isolated working face in worked-out area in deep mine was derived and applied to the isolated working face 3201 in worked-out area, thus comprehensively determining that the width of coal pillars should be 130m. The field stress monitoring verified the reasonability. The research result is of great significance to prevention of rock burst induced by coal pillars of isolated working face in worked-out area in deep mine.

Download Full-text

Analysis on Rock Burst Risks and Prevention of a 54 m-Wide Coal Pillar for Roadway Protection in a Fully Mechanized Top-Coal Caving Face

Shock and Vibration ◽

10.1155/2021/5584411 ◽

2021 ◽

Vol 2021 ◽

pp. 1-7

Author(s):

Zhihua Li ◽

Ke Yang ◽

Jianshuai Ji ◽

Biao Jiao ◽

Xiaobing Tian

Keyword(s):

Coal Seam ◽

Rock Burst ◽

Influencing Factors ◽

Abutment Pressure ◽

Large Diameter ◽

Coal Pillar ◽

Distribution Characteristics ◽

Pressure Relief ◽

Working Face ◽

Coal Pillars

A case study based on the 401103 fully mechanized caving face in the Hujiahe Coal Mine was carried out in this research to analyze the rock burst risks in a 54 m-wide coal pillar for roadway protection. Influencing factors of rock burst risks on the working face were analyzed. Stress distribution characteristics on the working face of the wide coal pillar for roadway protection were discussed using FLAC3D numerical simulation software. Spatial distribution characteristics of historical impact events on the working face were also investigated using the microseismic monitoring method. Results show that mining depth, geological structure, outburst proneness of coal strata, roof strata structure, adjacent mining area, and mining influence of the current working face are the main influencing factors of rock burst on the working face. Owing to the collaborative effects of front abutment pressure of the working face and lateral abutment pressure in the goaf, the coal pillar is in the ultimate equilibrium state and microseismic events mainly concentrate in places surrounding the coal pillars. Hence, wide coal pillars become the regions with rock burst risks on the working face. The working face adopts some local prevention technologies, such as pressure relief through presplitting blasting in roof, pressure relief through large-diameter pores in coal seam, coal seam water injection, pressure relief through large-diameter pores at bottom corners, and pressure relief through blasting at bottom corners. Moreover, some regional prevention technologies were proposed for narrow coal pillar for roadway protection, including gob-side entry, layer mining, and fully mechanized top-coal caving face with premining top layer.

Download Full-text

Stability of Coal Pillar and Roof Movement Characteristics in Roadway Backfill Mining

Advances in Civil Engineering ◽

10.1155/2021/5588923 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Hai Lin ◽

Renshu Yang ◽

Yongliang Li ◽

Shizheng Fang

Keyword(s):

Mechanical Model ◽

Maximum Stress ◽

Coal Pillar ◽

Engineering Practice ◽

Alternate Bearing ◽

Local Pressure ◽

Immediate Roof ◽

Backfill Mining ◽

Coal Pillars ◽

The Stability

In order to explore the stability of coal pillar and the characteristics of roof movement during the process of roadway backfill mining (RBM), the 301 backfilling test working face of Ordos Chahasu coal mine is taken as the background. Based on the expansive pressure arch theory, the evolution process of the stope expansive pressure arch in RBM is studied; by establishing a mechanical model for the stability of coal pillars, the interactions between the height, width, and the maximum number of branches are obtained. When the width and height of the branch are both 5 m, the optimal number of the branches is obtained. Then, by establishing a mechanical model for the subsidence of the immediate roof, the process of the immediate roof subsidence is divided into three stages, namely, the formation stage of the local pressure arch, the merge stage of the pressure arch, and the expansion stage of the pressure arch. In addition, using the numerical method, the alternate bearing process of coal pillars and filling bodies and the change of the maximum supporting stress are studied, and the evolution of the pressure arch bearing structure above the stope and the staged subsidence characteristics of the roof are analyzed. The on-site test showed that the coal pillar has a good stability during the mining process. The maximum stress of the coal pillar is 16.5 MPa, and the maximum stress of the filling body is 9 MPa. The maximum settlement of the immediate roof is 102 mm, indicating that the roof control effect is good. This research will play an important role on engineering practice.

Download Full-text

Stress Analysis of Negative Coal Pillar Gob-Side Entry and Its Principle of Preventing Rock Burst

Shock and Vibration ◽

10.1155/2020/8887165 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Zhiqiang Wang ◽

Peng Wang ◽

Lei Shi ◽

Wenyu Lv ◽

Chao Wu ◽

...

Keyword(s):

Stress Concentration ◽

Rock Burst ◽

Longwall Mining ◽

Limit Equilibrium ◽

High Stress ◽

Coal Pillar ◽

Stress Transfer ◽

Peak Stress ◽

Solid Coal ◽

Seam Mining

Gob-side entry is an area where it is difficult to prevent and control the frequent occurrence of rock burst. Based on “Longwall Mining with Split-level Gateways” (LMSG), this paper puts forward the technology of preventing rock burst by a new gob-side entry (NCPG). The abutment pressure distribution of LMSG shows that the stress peak of solid coal is lower than the conventional panel, and the width of the limit equilibrium zone is also reduced by a small percentage. After the narrow coal pillar gob-side entry has been excavated, the peak stress in solid coal increases, and the width of the limit equilibrium zone decreases, so the practical stress concentration increases. However, the NCPG located in areas of lower stress. The peak stress in solid coal of the NCPG does not increase, but the width of the limit equilibrium zone increases, so the practical stress concentration decreases. NCPC makes the concentrated stress transfer into the deep coal body and plays the role of pressure avoidance. Compared with the narrow coal pillar gob-side entry, the NCPG reduces the energy stored in coal and rock masses and increases the energy consumption. It has significantly improved the regionality, initiative, safety, and timeliness of rock burst prevention in deep high-stress coal seam mining.

Download Full-text

Design a Reasonable Width of Coal Pillar Using a Numerical Model. A case study of Khe Cham basin, Vietnam

E3S Web of Conferences ◽

10.1051/e3sconf/202017401043 ◽

2020 ◽

Vol 174 ◽

pp. 01043

Author(s):

Phuc Le Quang ◽

Vladimir Zubov ◽

Thang Pham Duc

Keyword(s):

Numerical Simulation ◽

Coal Pillar ◽

Linear Increase ◽

Underground Mines ◽

Support Pressure ◽

Efficient Production ◽

Mining System ◽

Geological Conditions ◽

Coal Pillars ◽

Roadway Deformation

Problems in surrounding rock displacement, roadway deformation and complex support are the hallmarks of the long wall mining system. Such problems seriously affect the safety and efficient production of coal mines. To control the deformation of the rocks around the roadway next to the goaf, to reduce the support pressure, in Vietnamese underground mines often leave supporting coal pillars. Identification of a reasonable design for roadway supporting pillars by a numerical simulation study was conducted under the geological and technical foundation of I-10- 2 working faces at the Khe Cham coal mine, Vietnam . The characteristics of stress and pressure distribution of roof layers on coal pillars are modeled under different pillar widths. The results show a great linear increase of the vertical stress on the narrow coal pillar and as the width of the coal pillar increases, the area of the elastic core area also increases and the level of stress increase tends to be stable without any apparent uptrend. Coal pillar deformation decreases with increasing coal pillar width, but it leads to large coal loss and waste of resources. Therefore, with the current supporting solutions to increase the stability of the coal pillar, the size range of a coal pillar is determined to be 6-8 m through numerical simulation. The conclusions obtained may provide a certain reference number to choose the logical location of the furnace lines under similar geological conditions.

Download Full-text

Effect of peak stress and deformation history on the dynamic tensile behavior of a dual phase steel

10.1063/12.0000820 ◽

2020 ◽

Author(s):

J.P. Escobedo ◽

A.A.H. Ameri ◽

M. Gonzales ◽

R. Miller ◽

H. Wang ◽

...

Keyword(s):

Dual Phase Steel ◽

Peak Stress ◽

Tensile Behavior ◽

Dual Phase ◽

Deformation History ◽

Stress And Deformation

Download Full-text

Trailing Edge Filings and a Modified Stodola’s Slip Factor for Centrifugal Impeller

Volume 1: Aircraft Engine; Fans and Blowers; Marine ◽

10.1115/gt2015-42874 ◽

2015 ◽

Author(s):

Guang Xi ◽

Huijing Zhao ◽

Zhiheng Wang

Keyword(s):

Numerical Simulations ◽

Good Accuracy ◽

Centrifugal Impeller ◽

Pressure Side ◽

Compressor Stage ◽

Trailing Edge ◽

Obvious Effect ◽

Quantitative Calculation ◽

Slip Factor ◽

Stage Efficiency

The paper investigates the effect of trailing edge filing in the impeller on the performances of impeller and compressor stage. The 3D viscous numerical simulations are carried out under different positions, thicknesses and lengths of filing. The results show that, the filing on the trailing edge has an obvious effect on the pressure ratios of impeller and compressor stage. The trailing edge filing has little effect on the impeller efficiency while the filing on the pressure side is favorable to improving the stage efficiency. Then, through correcting the blade angles at the suction and pressure sides, considering the viscosity and 3D characteristics of the flow, a modified slip factor formula is proposed for the centrifugal impeller with a trailing edge filing. The validation to the proposed formula shows that the proposed formula can be used to predict the slip factors of different filing cases with a good accuracy. It can provide a theoretical guidance for the quantitative calculation when using the filing technology to improve the performance of centrifugal impeller as well as the stage.

Download Full-text