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 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 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.

Numerical Investigation of the Minimum Roof Thickness of Mining Stope in Bailing Copper-Zinc Mine

2014 ◽  
Vol 670-671 ◽  
pp. 668-673
Author(s):  
Jiang Feng Ma ◽  
Xiu Li Zhang ◽  
Yu Yong Jiao ◽  
Hu Nan Tian
Keyword(s):  
Rock Mass ◽  
Numerical Model ◽  
Stress Distribution ◽  
Numerical Investigation ◽  
Damage Zone ◽  
Three Dimensional ◽  
Surface Displacement ◽  
Ore Body ◽  
Zinc Mine ◽  
Copper Zinc

A three-dimensional numerical model of the rock mass including ore body is established by FLAC3D software, and then the surface subsidence caused by backfilling under different roof thicknesses of mining stope (the vertical distance between upper mining limit and surface) are calculated and analyzed. By comparing the surface displacement, the stress distribution, and the damage zone under different conditions, the minimum roof thickness is determined.

scholarly journals TOMOGRAPHY BASED ON THE REPRESENTATION OF THE MODEL BY CHIBYSHEV POLYNOMIALS: EXAMPLES OF USE

2019 ◽  
Vol 2 (3) ◽  
pp. 154-159
Author(s):  
Maxim Protasov ◽  
Dmitry Neklyudov ◽  
Leonid Nazarov
Keyword(s):  
Rock Mass ◽  
Ray Tracing ◽  
Efficient Algorithm ◽  
A Priori ◽  
Three Dimensional ◽  
Stress Fields ◽  
A Priori Information ◽  
Travel Time Tomography ◽  
Coal Rock ◽  
Priori Information

The paper deals with the three-dimensional travel-time tomography of the first arrivals. The model is represented by Chebyshev polynomials. This allows one to use a priori information about the model effectively and reduce the number of recoverable parameters to the required minimum. Also, such a model representation makes it possible to obtain a very efficient algorithm for solving the two-point ray-tracing problem for three-dimensional media, which is necessary for tomography. Examples of solving the three-dimensional cross-well tomography, as well as examples using tomography for the reconstruction of stress fields in the coal-rock mass are presented.

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.

Three-Dimensional Numerical Simulation of the Mass Exchange Between Longwall Headings and Goafs, in the Presence of Methane Drainage in A U-Type Ventilated Longwall / Symulacja Numeryczna 3D Procesów Wymiany Masy W Układzie Wyrobiska Ścianowe Zroby, W Aspekcie Prowadzenia Odmetanowania Ściany Przewietrzanej Systemem Na „U”

2013 ◽  
Vol 58 (3) ◽  
pp. 705-718
Author(s):  
Przemysław Skotniczny
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Coal Seam ◽  
Mass Exchange ◽  
Experimental Analysis ◽  
Three Dimensional ◽  
Underground Mines ◽  
Test Cases ◽  
Methane Drainage ◽  
Invaluable Tool

Abstract The phenomena related to the occurrence of methane in underground mines pose a considerable danger in the process of coal seam exploitation. Quite often, experimental analysis falls short of investigating their areas of origin (goafs area, affected rock mass, the tail gate area with abandoned excavation). Therefore, an invaluable tool for evaluating the risk involved in the exploitation process might be the numerical simulation of the phenomenon in question, carried out with the use of the latest CFD methods. Due to its application, we are able to recreate and predict the mechanism of the studied phenomenon, with certain assumptions and simplifications made. The present paper discusses the results of the numerical simulation of the process of mass exchange occurring between affected rock mass and longwall headings. The calculations were performed for two test cases - 100 meter long walls.

scholarly journals Study on the Technology of Enhancing Permeability by Millisecond Blasting in Sanyuan Coal Mine

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Dan Zhao ◽  
Mingyu Wang ◽  
Xinhao Gao
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Simulation Software ◽  
Low Permeability ◽  
Time Interval ◽  
Rock Blasting ◽  
Deep Hole ◽  
Coal Seams ◽  
Coal Rock ◽  
Gas Coal

To reduce gas disasters in low permeability and high-gas coal seams and improve gas predrainage efficiency, conventional deep-hole presplitting blasting permeability increasing technology was refined and perfected. The numerical calculation model of presplitting blasting was established by using ANSYS/LS-DYNA numerical simulation software. The damage degree of coal and rock blasting was quantitatively evaluated by using the value range of the damage variable D. According to the actual field test parameters of coal seam #3 in the Sanyuan coal mine, Dlim = 0.81–1.0 was the coal rock crushing area, Dlim = 0.19–0.81 was the coal rock crack area, and Dlim = 0–0.19 was the coal rock disturbance area. By comparing and analysing the damage distribution nephogram of coal and rock mass under the influence of different millisecond blasting time interval and the blasting effect of simulation model, the optimal layout parameters of multilayer through cracks were obtained theoretically. And, the determined parameters were tested on the working face of the 1312 transportation roadway in coal seam #3 of the Sanyuan coal mine. The permeability effect was compared and analysed through the analysis of the gas concentration, gas purity, and mixing volume before and after the implementation of deep-hole presplitting blasting antireflection technology, as well as the change of gas pressure, attenuation coefficient, permeability coefficient, and other parameters between blasting coal seams. The positive role of millisecond blasting in reducing pressure and increasing permeability in low permeability and high-gas coal seam were determined.

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.

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