scholarly journals Field and simulation study of the rational coal pillar width in extra‐thick coal seams

2019 ◽  
Vol 8 (3) ◽  
pp. 627-646 ◽  
Author(s):  
Wenrui He ◽  
Fulian He ◽  
Yongqiang Zhao
Keyword(s):  
Simulation Study ◽  
Coal Pillar ◽  
Pillar Width ◽  
Coal Seams

scholarly journals Recovery Technology of Bottom Coal in the Gob-Side Entry of Thick Coal Seam Based on Floor Heave Induced by Narrow Coal Pillar

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3368 ◽  
Author(s):  
Kai Wang ◽  
Yanli Huang ◽  
Huadong Gao ◽  
Wen Zhai ◽  
Yongfeng Qiao ◽  
...  
Keyword(s):  
Coal Pillar ◽  
Resource Recovery ◽  
Complex Stress ◽  
Pillar Width ◽  
Coal Seams ◽  
Thick Coal Seam ◽  
Working Face ◽  
Floor Heave ◽  
Mining Face ◽  
Failure Depth

To improve the resource recovery efficiency of mining face in thick coal seams, the correlation between deformation failure of bottom coal in the gob-side entry and coal pillar width was analyzed by theoretical analysis, numerical calculation, and similar simulation experiments. The results showed that, when the coal pillar was strong, with the decrease of pillar width, the failure depth of the bottom coal in the gob-side entry and floor heave increased. The deformation failure depth of the bottom coal in the entry was inversely related to the width of the coal pillar. The bottom coal was further fractured and dispersed under the action of tension, shear, and extrusion in the process of floor heave. Based on the floor heave induced by the narrow coal pillar, a recovery technique of the bottom coal with thick coal seams in the gob-side entry was developed. The width of the narrow pillar to be reserved was obtained by theoretical calculation and revised by numerical simulation; ultimately, the reasonable width was determined. Under the complex stress of the narrow pillar, the bottom coal in the gob-side entry was fully heaved, cracked, and separated. To realize the comprehensive mechanization and resource recovery of bottom coal, a matching mining excavator loader, transfer conveyor, and retractable belt conveyor were selected to transport the crushed bottom coal in the entry. This method has been successfully applied to the return airway of working face 8407 in the No. 5 Coal Mine of Yangquan Coal Group with remarkable economic and social benefits.

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

2019 ◽  
Vol 16 (3) ◽  
pp. 559-570 ◽  
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.

Distribution of Underground Pressure Law and Fracture Zone Prediction Research of Overburden in Steep and Multiple Coal Seams Mining

2013 ◽  
Vol 448-453 ◽  
pp. 3888-3892
Author(s):  
Ke Min Wei ◽  
Mao Sen Zhao ◽  
Ze Kang Wen ◽  
You Ling Fang
Keyword(s):  
Stress Concentration ◽  
Coal Mining ◽  
Fracture Zone ◽  
Coal Pillar ◽  
Steep Seam ◽  
Coal Seams ◽  
Level 1 ◽  
Mining Work ◽  
Seam Mining ◽  
Protection Pillar

Use Taiping coal mines second horizontal (+1100m~+900 m level ) 1#, 3# and 5# coal seam in Panzhihua Baoding as the research object, apply the problem solving nonlinear large deformation finite difference method (FLAC), to research the steep multi-seam mining of pressure distribution and characteristics of fracture zone. The results show that: (1)During the course of three coal mining extraction, the stress of goaf surrounding rocks will be changed. (2)When the nearby coal is mining, the coal pillar come into being stress concentration near the area. when the mining work continues, the goaf will have an effect on the protection pillar, which is similar to the "liberate". the effect of coal pillar and stress concentration nearby will be eased; (3)After the coal mining, plastic failure has occurred over the protection pillar, forming a water guide channel. Research results can be as a reference for similar steep seam mining.

scholarly journals Stability of Split-Level Gob-Side Entry in Ultra-Thick Coal Seams: A Case Study at Xiegou Mine

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 628 ◽  
Author(s):  
Junwen Zhang
Keyword(s):  
Coal Mine ◽  
Coal Pillar ◽  
Peak Stress ◽  
Coal Seams ◽  
Solid Coal ◽  
Stress Fluctuation ◽  
Pillar Mining ◽  
The Stability ◽  
Rock Specimens

Split-level longwall gob-side entry (SLGE) has been applied as a special form of small gate pillar mining (or non-coal pillar mining) in thick coal seams. The stability of the coal pillar directly affects the rationality of the layout of the SLGE. Starting from the mining-induced influence around the SLGE, this paper compares the mechanical properties of coal under different mining effects, and studies the rationality of “zero pillar” location against the Xiegou coal mine. The study shows that the key to success of the application of the SLGE is the existence of an intact zone within the triangular coal pillar in spite of double disturbances due to tunneling and coal mining extraction. Laboratory testing shows that the density and uniaxial compressive strength of rock specimens obtained from the triangular coal pillar are smaller than that from the other part of the panel which is concluded to be due to the varied degree of mining-induced influence. The numerical modeling results show that most of the triangular coal pillar is intact after extraction of the panel, and that the peak stress is located in the solid coal beyond the triangular coal pillar. The plastic zone of the triangular coal pillar is only about 1 m after the excavation of the tail gate of the next split-level panel. The physical modeling shows that the tail gate of the next panel is in the destressed zone with only a very small stress fluctuation during the extraction of the next panel. The study shows that the location of the SLGE at Xiegou coal mine is reasonable. SLGE is preferable for ultra-thick coal seams.

scholarly journals Stability Analysis and Derived Control Measures for Rock Surrounding a Roadway in a Lower Coal Seam under Concentrated Stress of a Coal Pillar

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Zhuoyue Sun ◽  
Yongzheng Wu ◽  
Zhiguo Lu ◽  
Youliang Feng ◽  
Xiaowei Chu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Numerical Simulations ◽  
Principal Stress ◽  
Coal Pillar ◽  
Control Measures ◽  
Stress Difference ◽  
Coal Seams ◽  
The Stability ◽  
Close Distance ◽  
Close Distance Coal Seams

Numerical simulations have often been used in close-distance coal seam studies. However, numerical simulations can contain certain subjective and objective limitations, such as high randomness and excessively simplified models. In this study, close-distance coal seams were mechanically modeled based on the half-plane theory. An analytical solution of the floor stress distribution was derived and visualized using Mathematica software. The principal stress difference was regarded as a stability criterion for the rock surrounding the roadway. Then, the evolution laws of the floor principal stress difference under different factors that influence stability were further examined. Finally, stability control measures for the rock surrounding the roadway in the lower coal seam were proposed. The results indicated the following: (1) The principal stress difference of the floor considers the centerline of the upper coal pillar as a symmetry axis and transmits radially downward. The principal stress difference in the rock surrounding the roadway gradually decreases as the distance from the upper coal pillar increases and can be ranked in the following order: left rib > roof > right rib. (2) The minimum principal stress difference zones are located at the center of the left and right “spirals,” which are obliquely below the edge of the upper coal pillar. This is an ideal position for the lower coal seam roadway. (3) The shallowness of the roadway, a small stress concentration coefficient, high level of coal cohesion, large coal internal friction angle, and appropriate lengthening of the working face of the upper coal seam are conducive to the stability of the lower coal seam roadway. (4) Through bolt (cable) support, borehole pressure relief, and pregrouting measures, the roof-to-floor and rib-to-rib convergence of the 13313 return airway is significantly reduced, and the stability of the rock surrounding the roadway is substantially improved. This research provides a theoretical basis and field experience for stabilizing the lower coal seam roadways in close-distance coal seams.

scholarly journals Calculation and Application on Elastic-Plastic Coal Pillar Width of the Stope

2011 ◽  
Vol 26 ◽  
pp. 1116-1124 ◽  
Author(s):  
Jia Shuang-Chun ◽  
Wang Jia-chen ◽  
Zhu Jian-ming
Keyword(s):  
Coal Pillar ◽  
Pillar Width ◽  
Elastic Plastic

Research of New Filling and Mining Technology Using Waste Rocks in Steep Coal Seams

2012 ◽  
Vol 204-208 ◽  
pp. 1395-1400
Author(s):  
Chuan Wei Zang ◽  
Chuan Le Ma ◽  
Xue An Zhuang
Keyword(s):  
Coal Mining ◽  
Coal Pillar ◽  
Recovery Ratio ◽  
Mining Method ◽  
Coal Seams ◽  
Coal Recovery ◽  
Waste Rocks ◽  
Filling Method ◽  
Gob Area ◽  
Coal Pillars

During the extraction of steeply inclined coal seams, the coal recovery ratio is low be-cause of the coal pillar loss and the production of waste rock is high due to lots of rock roadways which causes serious environmental pollution. This status is conflicted with the strategy of Clean Coal Mining and Green Coal Mining in China, so it is necessary to develop new coal mining method. In this paper, Downward Stratified Gangue Self-filling Method on the Flexible Shield (DSGSMFS) is put forward first. It means that the coal face is lain horizontally and advances along the dip; the flexible shield is used to separate the gob area; the waste rocks are self-filled downward to the top the shield; the coal is broken by drilling and blasting method under the shield, and the broken coal is transported by the electrical winch and the scraping mucker; the flexible shield moves downward automatically by the weight of itself and waste rocks. Field test shows that the strata displacement is effectively controlled by using DSGSMFS, so some coal pillars are recovered; as a result the problem of large quantity gangue and low coal recovery ratio in steep coal seam is solved. DSGSMFS is proved to be a new hopeful and effective coal green mining method.

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