Effect of mining parameters on surface deformation and coal pillar stability under customized shortwall mining of deep extra-thick coal seams

The rockburst hazard has always been an important issue affecting the safety production of coal mines in China. The unreasonable sequencing of roadway driving can lead to the dynamic instability of coal pillars, which subsequently causes rockburst accidents in roadway backfilling mining engineering and poses a serious threat to the safety of the mines. Roadway backfilling mining technology is an effective approach with which to mine corner residual coal resources under buildings, railways, and rivers. An energy density criterion is established and programmed with FISH language using numerical analysis software for the rockburst risk evaluation of coal pillars. On this basis, a numerical simulation model is established based on four scheme types, namely, the sequential mining, one-roadway interval mining, two-roadway interval mining, and three-roadway interval mining schemes. The influence of the backfilling roadway driving sequence on coal pillar stability is investigated, and the change law of vertical stress and energy density factor of coal pillars in different driving sequences in roadway backfilling mining technology are analyzed. According to the research results, the maximum energy density factor value of 21,172 J/m4 for coal pillars in one-roadway interval mining is the lowest among the different schemes. Therefore, the one-roadway interval mining scheme is the optimal choice in roadway backfilling mining technology. The results can be treated as an important basis for the prevention and treatment of coal pillar instability and rockburst in roadway backfilling mining technology.

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Review of coal pillar lifespan prediction for the Witbank and Highveld coal seams

Journal of the Southern African Institute of Mining and Metallurgy ◽

10.17159/2411-9717/2016/v116n11a11 ◽

2016 ◽

Vol 116 (11) ◽

pp. 1083-1090 ◽

Cited By ~ 1

Author(s):

J.N. van der Merwe

Keyword(s):

Coal Pillar ◽

Coal Seams

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Developing coal pillar stability chart using logistic regression

International Journal of Rock Mechanics and Mining Sciences ◽

10.1016/j.ijrmms.2012.09.004 ◽

2013 ◽

Vol 58 ◽

pp. 55-60 ◽

Cited By ~ 38

Author(s):

R.K. Wattimena ◽

S. Kramadibrata ◽

I.D. Sidi ◽

M.A. Azizi

Keyword(s):

Logistic Regression ◽

Coal Pillar ◽

Pillar Stability ◽

Stability Chart

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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.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.448-453.3888 ◽

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.

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

Energies ◽

10.3390/en12040628 ◽

2019 ◽

Vol 12 (4) ◽

pp. 628 ◽

Cited By ~ 4

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.

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

Shock and Vibration ◽

10.1155/2020/6624983 ◽

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.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.204-208.1395 ◽

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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Modeling the Spatial and Temporal Evolution of Stress during Multiworking Face Mining in Close Distance Coal Seams

Advances in Civil Engineering ◽

10.1155/2021/5624972 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Yong Zhang ◽

Jinkun Yang ◽

Jiaxuan Zhang ◽

Xiaoming Sun ◽

Chen Chen ◽

...

Keyword(s):

Numerical Simulation ◽

Stress Distribution ◽

Temporal Evolution ◽

Coal Pillar ◽

Coal Seams ◽

Geological Conditions ◽

Coal Pillars ◽

The Stability ◽

Close Distance ◽

Close Distance Coal Seams

Mining in close distance coal seams (CDCSs) is frequently associated with engineering disasters because of the complicated nature of stress distribution within CDCSs. In order to establish a layout of a roadway to minimize the occurrence of disasters associated with mining CDCS, here the spatial and temporal evolution of stress distribution during the multiworking face mining of a CDCS was explored through numerical simulation based on the engineering and geological conditions of the Nantun Coal Mine. The numerical simulation results indicate that, after the extraction of adjacent multiple working faces, the spatial distribution of stress can be characterized with areas of increased, reduced, and intact stress. The superposed stress of inclined seams that are very close to each other propagates through coal pillars in the bottom floor, and this propagation follows neither the line along the axis of the coal pillar nor the line perpendicular to the direction of the floor. It instead propagates along a line angled with the axis of the coal pillar. The roadway can be arranged in the area with reduced stress, to improve its the stability. Based on the computed spatial and temporal evolution of stress, an optimized layout of roadway was proposed. This layout features a reasonable interval between the mining roadway and a minimal proportion of increased stress areas along the mining roadway and is aligned with geological structures.

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Analysis of the Control Effect and Influencing Factors of Urban Surface Deformation in Underground Coal Mining With Solid Backfilling

10.21203/rs.3.rs-221271/v1 ◽

2021 ◽

Author(s):

Jiaqi Wang ◽

Zhang Qiang ◽

Zhongya Wu ◽

Weijian Song ◽

Hao Zhang ◽

...

Keyword(s):

Compression Ratio ◽

Surface Deformation ◽

Coal Pillar ◽

Deformation Monitoring ◽

Surface Subsidence ◽

Reference Station ◽

Urban Mining ◽

Probability Integral Method ◽

Building Set ◽

Effective Angle

Abstract To solve the problems of surface deformation and destruction of buildings caused by urban mining and realise coordinated development of mining cities, the solid backfilling method was used to extract coal resources beneath the buildings of Tangshan. Based on surface deformation monitoring data of the continuously operating reference station (CORS) system for the past 5 years, the surface deformation process caused by solid backfilling was analysed. The final results revealed a maximum surface subsidence of 66 mm in the T zone coal area and 31 mm in the F zone area. Furthermore, the surface control effects of the caving method and the solid backfilling method were compared and analysed, and it was shown that solid backfilling could meet the surface building set-up requirements. Moreover, based on the probability integral method, the effects on surface deformation due to the surface length of the F zone, compression ratio, and coal pillar width were analysed, and the effects on the prediction results due to the subsidence factor, tangent of the major effective angle, and offset distance of the inflection point were studied. The results showed that the compression ratio is the main factor controlling the surface deformation and that it should be kept above 80% for solid backfilling of urban mines. The subsidence factor should be 0.82 and the tangent of the major effective angle should be 2.15 when the surface subsidence of solid backfilling is to be predicted. This paper provides a technical reference for realisation of urban mining with solid backfilling.

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