scholarly journals Mechanical Analysis of Mining Stress Transfer on Isolated Island Face in Extra-Thick Fully Mechanized Top-Coal Caving Mining

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Min Tu ◽  
Qingwei Bu ◽  
Baojie Fu ◽  
Yu Wang
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Estimation Method ◽  
Stress Transfer ◽  
Mechanical Analysis ◽  
Distribution Characteristics ◽  
Coal Wall ◽  
Coal Rock ◽  
Failure Depth

The mining spatial structure of isolated island face in extra-thick fully mechanized top-coal caving mining is unique, which leads to a complex mining stress distribution and serious safety hazards. In this study, combined with a specific engineering example, the mining stress distribution characteristics of isolated island face are expounded, and a bearing structural mechanical model of the continuous beam of overlying strata is established using elastic–plastic mechanics theory. The mechanical equations of the mining stress distribution and failure depth of coal–rock mass are then obtained. Comparison of theoretical calculation results with numerical simulation and field measurement results shows basically consistent stress distribution characteristics. The derived mechanical equations can provide an estimation method for the analysis of mining dynamics on isolated island face in extra-thick fully mechanized top-coal caving mining. The following conclusions are acquired. The coal–rock mass should bear not only the lateral mining superposition influence but also the advance mining influence in front of the coal wall, so the isolated island face is in the complex environment of multiple mining stress superposition. In the mining process, the maximum advance mining stress concentration factor is 4.0–6.0 and is located at the upper and lower ends of the isolated island face. The lateral mining failure depth of the coal wall of the isolated island face increases by 2.0–5.0 m under the influence of advance mining. Therefore, compared with the nonisolated island face, the mining pressure appearance is intense. The mining influence in the range of 20–30 m of the upper and lower ends is intense, and the mining stress in this area is characterized by “cone distribution.” This zone is an important hidden danger area with coal–rock mass mining instability on isolated island face, which requires special attention to avoid mining disasters. According to the analysis of the influencing mining factors and laws of isolated island face, it is concluded that the longer the isolated island face size is, the closer the goaf size on both sides of the isolated island face is, the smaller the coal seam buried depth is, the better the mechanical conditions of coal and rock medium are, and the smaller the mining height of coal seam is, the more favorable the safe mining of isolated island face is.

scholarly journals Reconstruction of 3D Micro Pore Structure of Coal and Simulation of Its Mechanical Properties

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Guang-zhe Deng ◽  
Rui Zheng
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Pore Structure ◽  
Three Dimensional ◽  
Low Permeability ◽  
Deformation And Failure ◽  
Coal Rock ◽  
Shear Failures ◽  
Negative Exponential

This article takes the low permeability coal seam in the coalfield of South Judger Basin in Xinjiang, as a research object. The pore structure characteristics of coal rock mass in low permeability coal seam were analyzed quantitatively using scanning electron microscopy (SEM) through the methods of statistics and digital image analysis. Based on the pore structure parameters and the distribution function of the coal rock mass, a three-dimensional porous cylinder model with different porosity was reconstructed by FLAC3D. The numerical simulation study of reconstructed pore model shows that (1) the porosity and the compressive strength have obvious nonlinear relation and satisfy the negative exponential relation; (2) the porosity significantly affects the stress distribution; with the increase of micro porosity, the stress distribution becomes nonuniform; (3) the compressive failures of different models are mainly shear failures, and the shape of fracture section is related to porosity; (4) the variation of seepage coefficient of the pore reconstruction model is consistent with the development of micro cracks. The micro mechanism of the deformation and failure of coal and the interaction of multiphase flow with porosity are revealed, which provides a theoretical reference for the clean development of the low permeability coal seam.

scholarly journals Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining: a case study

2021 ◽  
Author(s):  
Rui Wu ◽  
Penghui Zhang ◽  
Pinnaduwa H. S. W. Kulatilake ◽  
Hao Luo ◽  
Qingyuan He
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Abutment Pressure ◽  
Longwall Mining ◽  
Vertical Stress ◽  
Floor Level ◽  
Working Face ◽  
Floor Heave ◽  
Stress And Deformation

AbstractAt present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

scholarly journals Floor failure depth of upper coal seam during close coal seams mining and its novel detection method

2017 ◽  
Vol 36 (5) ◽  
pp. 1265-1278 ◽  
Author(s):  
Wei Zhang ◽  
Dongsheng Zhang ◽  
Dahong Qi ◽  
Wenmin Hu ◽  
Ziming He ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Mechanical Model ◽  
Coal Pillar ◽  
Coal Seams ◽  
Geological Conditions ◽  
Floor Failure ◽  
Calculation Results ◽  
Failure Depth ◽  
Close Coal Seams

The primary problem needed to be solved in mining close coal seams is to understand quantitatively the floor failure depth of the upper coal seam. In this study, according to the mining and geological conditions of close coal seams (#10 and #11 coal seams) in the Second Mining Zone of Caocun Coal Mine, the mechanical model of floor failure of the upper coal seam was built. Calculation results show that the advanced abutment pressure caused by the mining of the upper coal seam, resulted in the floor failure depth with a maximum of 26.1 m, which is 2.8 times of the distance between two coal seams. On this basis, the mechanical model of the remaining protective coal pillar was established and the stress distribution status under the remaining protective coal pillar in the 10# coal seam was then theoretically analysed. Analysis results show that stress distribution under the remaining protective coal pillar was significantly heterogeneous. It was also determined that the interior staggering distance should be at least 4.6 m to arrange the gateways of the #209 island coalface in the lower coal seam. Taken into account a certain safety coefficient (1.6–1.7), as well as reducing the loss of coal resources, the reasonable interior staggering distance was finally determined as 7.5 m. Finally, a novel method using radon was initially proposed to detect the floor failure depth of the upper coal seam in mining close coal seams, which could overcome deficiencies of current research methods.

The Research on Abutment Stress Distribution and Fracture Characteristics of Coal Seam in Longwall Face

2011 ◽  
Vol 361-363 ◽  
pp. 103-107
Author(s):  
Chuan Ming Li
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Surrounding Rock ◽  
Geometrical Shape ◽  
Horizontal Distance ◽  
Site Testing ◽  
Fracture Characteristics ◽  
Working Face ◽  
Coal Wall ◽  
Overlying Strata

The abutment stress results from the load coming from overlying strata above the influence range of abutment stress and the load which coming from overlying strata above the stress shell passed by the shell. Through the mechanical calculation,this paper analyzed abutment stress distribution and fracture characteristics of coal seam resulted from the load of overlying strata passed by stress shell which exists in surrounding rock of working face, and obtained the laws of abutment stress distribution and fracture in coal seam in combination with numerical simulation and site testing. The characteristics of abutment stress distribution and fracture are related to the geometrical shape of the stress shell, such as height of the stress shell, horizontal distance between top of stress shell and coal wall,and width of stress shell skewback.

Studies of the Stress State of the Coal Pillar between the Treatment andPreparatory Workings by the Methods of Deformable Body Mechanics

2020 ◽  
pp. 26-31
Author(s):  
N.V. Cherdantsev ◽  
Keyword(s):  
Rock Mass ◽  
Stress State ◽  
Coal Seam ◽  
Solid Mechanics ◽  
Boundary Integral Equations ◽  
Coal Pillar ◽  
Boundary Integral ◽  
External Boundary ◽  
Mining Operations ◽  
Coal Rock

To ensure safe conditions for mining operations and increase labor productivity, a reliable assessment of the stress state of the coal-rock mass is required. The model is presented concerning the geomechanical state of the massif hosting the coal seam, treatment, and preparatory workings. The model is developed based on the fundamental methods of solid mechanics and ensures a computational experiment and the reliability of the results. Stress distribution in the coal-rock mass in the vicinity of the in-seam workings was calculated in two stages. First, the stress field in the edge zones of the coal seam and in the collapsed rocks was determined by the methods of mechanics of the flowing medium. Distribution of stresses in the extremely stressed zones of the seam and the layer of collapsed rocks behind the working excavation was found by the method of characteristics by solving differential equations of the hyperbolic type. They are obtained based on the of the joint solution of the equilibrium equations, general and special Coulomb — Mohr criteria of the transition of the seam and the collapsed layer, as well as their contacts with the lateral rocks to the limiting state. Then, by replacing extremely stressed zones of the coal seam and the layer of the collapsed rocks with stresses acting at the contacts with the surrounding massif, the problem is reduced to the integral equation of the second external boundary value problem of the theory of elasticity. It is solved by the method of boundary integral equations. Insignificant influence of changes in the angle of internal friction of the collapsed rocks on the parameters of the seam bearing pressure in the vicinity of the treatment and development workings is shown. However, it significantly effects on the bearing pressure in the extremely stressed zone of the collapsed rocks layer.

scholarly journals Study on the Failure Characteristics of Coal Wall Spalling in Thick Coal Seam with Gangue

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Guosheng Li ◽  
Zhenhua Li ◽  
Feng Du ◽  
Zhengzheng Cao
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Internal Stress ◽  
External Stress ◽  
Theoretical Research ◽  
Risk Area ◽  
Thick Coal Seam ◽  
Failure Characteristics ◽  
Coal Wall ◽  
Stress Environment

Coal wall spalling is one of the main factors restricting the safe and efficient mining of thick coal seam, and the gangue has an important impact on the coal wall spalling. To obtain the failure characteristics of coal wall spalling in thick coal seam containing gangue, numerical calculation and theoretical research were used to analyze the morphological differences of coal wall spalling with different gangue positions. Besides, the damage depth, width, and stress environment of coal wall panel caused by the position of gangue were mainly studied, and the failure mechanics model of coal seam containing gangue was established by using the stability theory of pressure bar. The results show that, compared with coal wall spalling in coal seam without gangue, coal seam with the lower and middle gangue has a significant weakening effect on the wall spalling, and coal seam with the upper gangue has little effect on the wall spalling. In the case of coal seam with gangue, the upper gangue has the highest risk area of coal wall spalling with the maximum depth and width of 2.0 m and 2.3 m. For coal seam with the upper gangue, the dangerous areas of coal wall spalling are mainly distributed in the vicinity of the gangue; for coal seam without the gangue, they are mainly distributed in the middle of the coal seam. The gangue cannot change the law of the external stress distribution of the coal seam, but it has an obvious impact on the internal stress distribution of the coal seam. With the different positions of the gangue, the stress distribution in the coal seam has a great difference, and the maximum difference is 1.8 MPa. This shows that the stress environment of the coal seam containing gangue has the following typical characteristics: “the external stress is controlled by the overburden fracture, and the internal stress environment is controlled by the gangue.” Through the mechanical analysis of the coal seam containing gangue, it is further verified that the coal seam containing gangue is more prone to spalling at the position of gangue.

Study on Underlying Coal and Strata Pressure-Relief Principle and the Gas Extraction Technique under Upper Protective Layer Mining

2014 ◽  
Vol 875-877 ◽  
pp. 1863-1870 ◽  
Author(s):  
Jian Liu ◽  
Jie Zhao ◽  
Ming Song Gao
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Protective Layer ◽  
Extraction Technique ◽  
Efficient Production ◽  
Gas Extraction ◽  
Pressure Relief ◽  
Fracture Development ◽  
Floor Heave ◽  
Coal Rock

By study on underlying coal and strata pressure-relief principle and the gas extraction technique under upper protective layer mining, we obtain the stress change and distribution law of underlying coal-rock mass. We analyze the deformation law and fracture development characteristics of underlying coal-rock mass movement. With mining proceeding ahead, the total floor coal and rock experiences compression deformation first, then expansion deformation and re-compaction of the continuous periodic destruction. Based on different development characteristics and status of underlying coal-rock mass, the underlying coal-rock mass under an effect of upper protective layer mining was divided into the floor heave fracture zone and the floor heave deformation zone in this paper. The permeability coefficient of change law of underlying the coal seam as follows: the original value-small decreasing-increasing greatly-reducing-stability at last. The field test for upper protective layer mining of Zhang-ji coal mine of Huainan shows that the effect of pressure relief of protected seam is very good. So it eliminates the risk of gas outburst, ensuring safety mining of the protected seam. The research has an important significance for safety and efficient production under similar exploitation conditions of low-permeability with high gas and outburst risk coal seam.

scholarly journals Impact of In Situ Stress Distribution Characteristics on Jointed Surrounding Rock Mass Stability of an Underground Cavern near a Hillslope Surface

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Bangxiang Li ◽  
Yong Li ◽  
Weishen Zhu ◽  
Chao Li ◽  
Zhenxing Dong
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
In Situ Stress ◽  
Surrounding Rock ◽  
Horizontal Distance ◽  
Distribution Characteristics ◽  
Slope Surface ◽  
Rock Mass Stability ◽  
Underground Cavern

In this paper, a series of numerical simulations are performed to analyze the in situ stress distribution characteristics of the rock mass near different slope angles hillslope surfaces, which are subjected to the vertical gravity stress and different horizontal lateral stresses and the influence which the in situ stress distribution characteristics of 45° hillslope to the integral stability of surrounding rock mass when an underground cavern is excavated considering three different horizontal distances from the underground cavern to the slope surface. It can be concluded from the numerical results that different slope angles and horizontal lateral stresses have a strong impact on the in situ stress distribution and the integral surrounding rock mass stability of the underground cavern when the horizontal distance from the underground cavern to the slope surface is approximately 100 m to 200 m. The relevant results would provide some important constructive suggestions to the engineering site selection and optimization of large-scale underground caverns in hydropower stations.

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