scholarly journals Numerical Investigation of Relationship between Bursting Proneness and Mechanical Parameters of Coal

2021 ◽  
Vol 2021 ◽  
pp. 1-28
Author(s):  
Hongwei Wang ◽  
Jiaqi Song ◽  
Zeliang Wang ◽  
Yue Zhang ◽  
Shaozhen Zhang ◽  
...  
Keyword(s):  
Numerical Model ◽  
Safety Concern ◽  
Distribution Functions ◽  
Plastic State ◽  
Shear Strain Rate ◽  
Mechanical Parameters ◽  
Stress Strain ◽  
Soft Coal ◽  
Geological Conditions ◽  
Coal Bursts

As one of the most catastrophic dynamic hazards in underground coal mines, coal bursts have been a major safety concern around the world for many years. Although the coal bursts can occur in all cases of hard to soft coal if the right stress environment is created, the occurrence of coal bursts is closely related to the intrinsic mechanical properties of coal, such as the bursting proneness. In this study, a total of 27 coal specimens are selected in the open literature studies to obtain a group of fundament data, such as the mechanical parameters, four bursting proneness indices, stress-strain curves, and their geological conditions where the specimens were taken. The relationship between bursting proneness indices and the cohesion of the coal specimens is established by numerically fitting the stress-strain curves and theoretically deduction. By taking into account the coal heterogeneity, eight probability distribution functions are employed to assignment nonuniform cohesion to the numerical model and to study the influence of heterogeneity on bursting proneness. The results reveal that the coal cohesion, which combines the common advantages of the four proneness indices, can be used as bursting proneness index. In the research of heterogeneity, the coal bursting proneness will decrease with the increasing of cohesion scatter degree. The larger the cohesion scatter degree increase is, the lower the bursting proneness will be. The failure of coal specimen is more and more severe with the decrease of cohesion scatter degree. In addition, this paper provides two methods for assigning heterogeneous parameters to the numerical model. The contours of shear strain rate and plastic state between homogeneous and heterogeneous coal specimens are compared to study the failure types of coal specimens and to reveal the mechanism of violent failure in coal bursts.

Analysis of Efficiency of Drilling of Large-Diameter Wells With a Profiled Wing Bit / Badania Efektywności Wiercenia Studni Wielkośrednicowych Świdrem Skrawającym z Profilowanymi Skrzydłami

2012 ◽  
Vol 57 (2) ◽  
pp. 363-373
Author(s):  
Jan Macuda
Keyword(s):  
Average Rate ◽  
Large Diameter ◽  
Open Pit ◽  
Mechanical Parameters ◽  
Drilling Rate ◽  
Geological Conditions ◽  
Rock Drillability ◽  
Drilling Technology ◽  
Weight On Bit ◽  
Rotary Speed

Abstract In Poland all lignite mines are dewatered with the use of large-diameter wells. Drilling of such wells is inefficient owing to the presence of loose Quaternary and Tertiary material and considerable dewatering of rock mass within the open pit area. Difficult geological conditions significantly elongate the time in which large-diameter dewatering wells are drilled, and various drilling complications and break-downs related to the caving may occur. Obtaining higher drilling rates in large-diameter wells can be achieved only when new cutter bits designs are worked out and rock drillability tests performed for optimum mechanical parameters of drilling technology. Those tests were performed for a bit ø 1.16 m in separated macroscopically homogeneous layers of similar drillability. Depending on the designed thickness of the drilled layer, there were determined measurement sections from 0.2 to 1.0 m long, and each of the sections was drilled at constant rotary speed and weight on bit values. Prior to drillability tests, accounting for the technical characteristic of the rig and strength of the string and the cutter bit, there were established limitations for mechanical parameters of drilling technology: P ∈ (Pmin; Pmax) n ∈ (nmin; nmax) where: Pmin; Pmax - lowest and highest values of weight on bit, nmin; nmax - lowest and highest values of rotary speed of bit, For finding the dependence of the rate of penetration on weight on bit and rotary speed of bit various regression models have been analyzed. The most satisfactory results were obtained for the exponential model illustrating the influence of weight on bit and rotary speed of bit on drilling rate. The regression coefficients and statistical parameters prove the good fit of the model to measurement data, presented in tables 4-6. The average drilling rate for a cutter bit with profiled wings has been described with the form: Vśr= Z ·Pa· nb where: Vśr- average drilling rate, Z - drillability coefficient, P - weight on bit, n - rotary speed of bit, a - coefficient of influence of weight on bit on drilling rate, b - coefficient of influence of rotary speed of bit on drilling rate. Industrial tests were performed for assessing the efficiency of drilling of large-diameter wells with a cutter bit having profiled wings ø 1.16 m according to elaborated model of average rate of drilling. The obtained values of average rate of drilling during industrial tests ranged from 8.33×10-4 to 1.94×10-3 m/s and were higher than the ones obtained so far, i.e. from 181.21 to 262.11%.

scholarly journals Coupling numerical model of hydraulic fracturing seepage in soft coal based on elastoplastic damage

2020 ◽  
Vol 198 ◽  
pp. 01038
Author(s):  
LI Liangwei
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Hydraulic Fracturing ◽  
Yield Criterion ◽  
Calculation Model ◽  
Field Application ◽  
Soft Coal ◽  
Plastic Shear Strain ◽  
Strain Relationship ◽  
Relationship Equation

In order to guide the field application of hydraulic fracturing of soft coal in coal mine, based on the elastic-plastic damage theory, the coupling numerical model of soft coal hydraulic fracturing seepage was studied. The porosity strain relationship equation, permeability strain relationship equation, the relationship between permeability and volume plastic tensile strain and volume plastic shear strain of coal and rock mass are derived, and the plastic correction equation and softening parameters are defined. The stress coupling equation and yield criterion are programmed and embedded into the finite difference software FLAC3D for numerical solution. The numerical simulation shows that the numerical calculation model of soft coal hydraulic fracturing conforms to the actual law, and the field fracturing radius investigation experiment is consistent with the numerical simulation results.

Improving Safety when Extracting Water-soluble Ores by Optimizing the Parameters of the Backfill Mass

2021 ◽  
pp. 53-59
Author(s):  
M.M. Khayrutdinov ◽  
◽  
Ch.B. Kongar-Syuryun ◽  
A.M. Khayrutdinov ◽  
Yu.S. Tyulyaeva ◽  
...  
Keyword(s):  
Strain State ◽  
Raw Materials ◽  
Research Work ◽  
Integrated Approach ◽  
Water Soluble ◽  
Mining Operations ◽  
Stress Strain ◽  
Mining System ◽  
Stress Strain State ◽  
Geological Conditions

The results of the scientific and research work devoted to modeling the stress-strain state of the mining system of an underground mine using the finite element method in the FLAC3D software are presented in the article. The possibility of using room-and-pillar mining with backfill with the abandonment of chain pillars is justified. The results are presented concerning the research results of the quantitative assessment of the mass using the von Mises equation and Norton' power law of creep to estimate the contour stress. It becomes possible to determine the sequence of mining of the deposit area and the stage-by-stage filling of the stopes at the stage of mining design due to the high accuracy of modeling the stress-strain state of the mass near mining operations using FLAC3D software. The proposed approach is possible when evaluating the geotechnical state of the rock mass when using the mining systems with various methods of support of the mined-out area: natural; artificial; with the collapse of ores and enclosing rocks, as well as when calculating the combined method of deposit development. A differentiated approach to assessing the state of the mass is possible considering difficult mining and geological conditions, conditions of increased rock pressure, abundant water influx, increased fracturing of rocks by introducing additional conditions into the model depending on its geotechnical state. Variant of the comprehensive exploitation of mineral resources was proposed considering the total value of natural and man-made geo-resources of the area being mined. The possibility of rational use of the mined-out space with the use of various positive qualities of geo-resources at their manmade transformation is also considered. An assessment of the mineral and raw materials potential of the mined area is given with a proposal for the prospects of increasing the integrated approach of excavation, increasing the life of the mining enterprise and the complexity of developing this area.

scholarly journals Stress−strain curves and derived mechanical parameters of P91 steel from spherical nanoindentation at a range of temperatures

2020 ◽  
Vol 194 ◽  
pp. 108950 ◽  
Author(s):  
Ana Ruiz-Moreno ◽  
Peter Hähner ◽  
Francesco Fumagalli ◽  
Vendulka Haiblikova ◽  
Marcello Conte ◽  
...  
Keyword(s):  
Mechanical Parameters ◽  
Stress Strain ◽  
P91 Steel

scholarly journals Microstudy of the Anisotropy of Sandy Material

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Kunyong Zhang ◽  
Zhenjun Zang ◽  
Leslie Okine ◽  
Jose Luis Chavez Torres
Keyword(s):  
Numerical Test ◽  
Strain Curve ◽  
Initial Stresses ◽  
Biaxial Test ◽  
Generation Process ◽  
Mechanical Parameters ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Axis Orientation ◽  
Inherent Anisotropy

Through numerical simulation based on the particle flow method, DEM numerical test samples were generated with the results of laboratory tests on standard sand. The method consists of the use of gravity deposition and radius expansion modeling of irregular sand particles, where samples of the biaxial test are assembled by generated long particle units. Different steps of deposition or initial stresses were applied during the sample generation process in order to simulate different sample states. The loads from the horizontal and vertical directions are, respectively, applied to samples, and then the stress-strain curve and macroscopic mechanical parameters are acquired. The numerical experiment results show that the gravitational deposits have significant impact on the major axis orientation arrangement of particles and on the average coordination number, as well as the initial stress has a significant effect on it. There is a remarkable effect on the stress-strain curve and on the acquired mechanical parameters as a result of the application of load to samples from the horizontal and vertical directions. The sand samples show an obvious property of inherent anisotropy and stress-induced anisotropy.

scholarly journals INVESTIGATION OF STRESS-STRAIN STATE OF CYLINDRICAL BODY OF MODIFIED HDPE

2019 ◽  
Vol 62 (7) ◽  
pp. 118-122
Author(s):  
Stepan V. Litvinov ◽  
Lyubov I. Lesniak ◽  
Serdar B. Yazyev ◽  
Ivan M. Zotov
Keyword(s):  
Ionizing Radiation ◽  
Strain State ◽  
Polymeric Materials ◽  
Cylindrical Body ◽  
Rheological Parameters ◽  
Scientific School ◽  
Mechanical Parameters ◽  
Principal Stresses ◽  
Stress Strain ◽  
Stress Strain State

The change in the stress-strain state over time in structures and their elements from polymeric materials can be quite substantial. This is due to the pronounced rheology of the polymers. One of the most accurate laws of stress-strain bond is generalized nonlinear Maxwell-Gurevich equation, which takes into account three rheological parameters: the modulus of elasticity, the velocity modulus and the coefficient of initial relaxation viscosity. A significant influence on the physico-mechanical parameters of the polymer is also exerted by various factors: the presence of a temperature field and ionizing radiation, the presence of additives in the polymer and so on. The paper presents the results of mathematical modeling of a disc made of high-density polyethylene (HDPE) in an axisymmetric setting under the influence of mechanical axial pressure. This model is chosen because of the most frequent use of HDPE irradiated and with additives in medicine, including for the manufacture of orthopedic prostheses. Different compositions of HDPE are considered: under the influence of ionizing radiation, with additives of hydroxyapatite and with their combined effect. All physico-mechanical parameters of HDPE (dose of ionizing radiation and the fraction of hydroxyapatite injected) are described by mathematical expressions obtained in the scientific school of Professor B.M. Yazyev on the basis of an analysis of the corresponding polymer relaxation curves. The results of the solution of the problem have shown that the basic stresses (radial, circumferential and axial) vary in the course of time in different ways. The growth of the value of the primary basic stresses can be 2-2.5 times. If the analysis is carried out on the main stresses, then their value increases by approximately 1.5 times. Also, the change in the principal stresses is observed even when it is not observed for the basic stresses.

scholarly journals Numerical Study on Soft Coal Pillar Stability in an Island Longwall Panel

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Qingyun Xu ◽  
Jian-Biao Bai ◽  
Shuai Yan ◽  
Rui Wang ◽  
Shaoxu Wu
Keyword(s):  
Plastic Zone ◽  
Numerical Study ◽  
Deformation Characteristic ◽  
Coal Pillar ◽  
Surrounding Rock ◽  
Pillar Width ◽  
Soft Coal ◽  
Geological Conditions ◽  
Longwall Panel ◽  
Coal Pillars

Roadway support and management of longwall panels in an island soft coal panel are always difficult work. In a test mine, stress distribution, deformation characteristic, and plastic zone distribution around the roadway and coal pillars in the development and mining periods were investigated with respect to the widths of different coal pillars using theoretical and simulation methods. The most reasonable width of coal pillars was comprehensively determined, and the field test was conducted successfully. The results show that a reasonable width of coal pillars is 7.0–8.2 m using the analytical method. The distribution of vertical stress in the coal pillars showed an asymmetric “double-hump” shape, in which the range of abutment pressure was about 26.0–43.0 m, and the roadway should be laid away from stress concentration. When the coal pillar width is 5.0–7.0 m, deformation of the roadway is half that with 8.0–10.0 m coal pillar in the development and mining period. The plastic zone in the surrounding rock firstly decreases and increases with increasing coal pillar width; the smallest range occurs with a coal pillar width of 5.0 m. Finally, a reasonable width for coal pillars in an island panel was determined to be 5.0 m. Industrial practice indicated that a coal pillar width of 5.0 m efficiently controlled deformation of the surrounding rock, which was an important basis for choosing the width of coal pillars around gob-side entries in island longwall panels with similar geological conditions.

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