Coupling Study Between Rheology and Electromagnetic Emission Of

Available online at www.sciencedirect.com Procedia

Engineering ProcediaProcedia Engineering Engineering 00 (20 2611 )(2011) 000–000 1571 – 1575 www.elsevier.com/locate/procedia

First International Symposium on Mine Safety Science and Engineering Coupling study between Rheology And Electromagnetic Emission of Coal or Rock dynamic catastrophe Xue Erlong a, Zhang Xiaopin a, He Xueqiu b , Zhao feic, liu xinnac, Guo Jianhuac,LI Hailongca*

aSafety Supervision Sector of Shenhua Group Limited Liability Company, Beijing, China bChina Academy of Safety Science & Technology, Beijing 100012, China cSchool of Resource and Safety Engineering, China University of Mining & Technology(Beijing), Beijing 100083, China

Abstract

This paper provides a theory of coal and rock rheological electromagnetic radiation coupling based on the generalized original model by using theoretical analysis, numerical simulation, field test and analysis of the coal rock material damage characteristics and strength statistics. On this basis, the software FLAC was used to simulate the roadway creep strain condition of # 2218 of Chengzhuang Coal Mine, and a research of electromagnetic radiation test on the tunnel was conducted. The practical testing results agree well with the analysis of theory. The results make contributions to the research on the usage of electromagnetic radiation and other disasters.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of China Academy of Safety Science and Technology, China University of Mining and Technology(Beijing), McGill University and University of Wollongong

Keyword: Coal petrography; creep deformation; simulation; electromagnetic radiation; tunnelling

1. Introduction

Coal and rock dynamic disaster is one of the most critical natural disasters. Coal and rock rheology can explain the phenomenon of coal and rock dynamic disasters because it considers the factor of time. Many experts have done much work on this and conducted research on the energy depleting theory. Based on this, the paper introduces the theory of coal and rock rheological electromagnetic radiation coupling, and provides the method of caculation by numerical simulation and the test of rheological electromagnetic radiation. These methods can provide the basis for forecasting such disasters.

* Corresponding author. Tel.: 010-58133125, 13522871533 E-mail address: [email protected]

2. The coupling relation between rheology and electromagnetic radiation

Rheology is mainly manifested in two aspects: creep and stress relaxation. Creep refers to the deformation process of coal and rock under constant load with time. Electromagnetic radiation of coal creep is an outward radiation of electromagnetic waves due to micro-cracking during the coal damage deformation in the loading of coal rock under constant stress with time. As time lapses, the creep strain of coal increases, thus the number of cracks produced by the coal deformation and fracture is as many as pulses of electromagnetic radiation. When the coal suffers more than it can bear, deformation rate increases and the intensity of electromagnetic radiation produced by coal becomes greater, which shows a positive correlation between both. The larger the coal creep strain, the stronger the electromagnetic radiation. So there is a relation between coal creep and creep damage of coal. In order to meet a variety of coal rheological test results, the generalized physical model of the West come to the original coal-D rheological constitutive equation (Eq. 1) based on strength statistics damage theory of coal and rock. It is concluded that according to the three dimensional rupture strength and stress of electromagnetic radiation, the two equations constitute the rheological electromagnetic radiation coupling equations. 1 3  3   E  1 c          2          sij ij m ij  1 exp t ( i j ij  )T , 0 y1 2G E1 2E2   H1  3  c 1 3 (1) sij   ij  m ij 2G E1     n    3  1  E2  0 yi  1    1 exp t   t        T ,   2 E   H   H i j 3 ij 0 yn  2   1  i2 i  

1   m   m  2 2W  N            E  0 m  exp  1 3    exp  1 3   (2) m V    E     E      0     0  

Where, S(c)ij - the three-dimensional creep rate tensor; G  E1 21  ;  - the Poisson’s ratio;

E1, E2 - the three-dimensional elasticity coefficient, Mpa;  ij - Kronecker sign; H1, Hi - the three-

dimensional viscosity coefficient, Mpa.d;  y1,, yi - the three-dimensional yield stress, Mpa;  0 - the

equivalent stress, Mpa; Tαβ- the three-dimensional effective stress deviation tensor; Em - the average electric field amplitude of the electromagnetic radiation field; W0 - the energy of the electromagnetic

radiation; Nm - the accumulative pulse amount of the electromagnetic radiation; V - the volume of the

coal and rock mass;  - the dielectric constant; D - electric displacement; ε 0- the distribution scale of the Weibull distribution and the form parameter represented by the strain form; E - the average elasticity

modulus of the non-injury coal rock mass unit; σ 1, σ 3- the principal stress denominated by the infinitesimal unit, MPa.

3. The rheology of head-on tunnel and the numerical simulation of electromagnetic radiation

In the tunnelling process of the coal, it appears the phenomenon of stress concentration in the head- on and the two-sides coal petrography under the crustal stress or the influence of the mining movement, thus causing deformation and dissipation of the energy produced which diffuses out in various energy forms, such as elastic deformation energy, electromagnetic radiation energy and heat energy. As time passes, the rheology occurs gradually in the tunnelling roadway, and the strain also increases gradually. XueXue Erlong Erlong et al. et /al Procedia / Procedia Engineering Engineering 26 00(2011) (2011 1571) 000 –– 1575000 15733

The #2218 tunnelling roadway of Chengzhuang Coal Mine in Jincheng Coal Group is taken as the model. FLAC3D software is adopted. The creep time is selected as 1 year. The roof of the coal seam is the sandstone at thickness of 2.5m. The immediate roof is mudstone at thickness of 6.27m. The average thickness of the coal seam is 3m. The analog computation in this paper does not consider the lean condition of the coal seam. The average mining depth in the simulation is 470m. If the rheological features of the roof and the floor are not considered. The simulation parameters of the coal seam are selected as follows: bulk modulus is 8.43GPa, shear modulus k is 3.45GPa, viscosity coefficient k is 6GPa, friction angle is 250, cohesion is 2.5Mpa, shear modulus is 2.5GPa, and viscosity coefficient is 6GPa.

3.1 The creep simulation result of the tunnelling roadway

As tunnelling begins, the surrounding rock stress redistributes, which causes the surrounding rock near the front of the tunnelling to move. After that, the surrounding rock in the roadway increases with time, and the coal petrography also creeps continuously. The paper chooses the simulation result obtained when the creep time is 0.5 year (Fig.1), 1 year (Fig.2). From Fig. 1 and Fig.2, it can be known that the creep decreases gradually from the roadway side to the inside (the x direction). This is because that the deformation of the coal and rock mass is relatively large after the roadway nearby is tunnelled. The strain becomes less and less along the tunnelling direction. The reason is that the closer the roadway goes towards the tunnelling surface, the bigger the tunnelling surface will be influenced. What’s more, as time passes, the strain diminishes gradually, and the simulation result accords with the theory and the actual situation of the project.

Fig. 1 The strain distribution of head-on tunnel (0.2 year) Fig. 2 The strain distribution of head-on tunnel (1 year)

3.2 Coupling simulation of electromagnetic radiation from creeping excavation roadway

Electromagnetic radiation will become more intense when the creeping becomes stronger due to strong stress. Substitute the value above to Formula 2, the results of different roadways are obtained. The paper chooses two points which are 4m and 5m away from the wall (Fig.3 and Fig.4). It can be seen from the two pictures that as time lapses, the electromagnetic radiation become low in general, which is because at the beginning of the creeping, the strain is higher and the electromagnetic radiation is stronger, too. Subsequently, the speed of strain slows, so does electromagnetic radiation. When the speed comes to zero, the electromagnetic radiation totally disappears, too. The result agrees with the theoretical analysis. 15744 XueXue Erlong Erlong et alet /al. Procedia / Procedia Engineering Engineering 00 26(2011 (2011)) 000 1571–000 – 1575 200

160

120

EME 80

0 1 36 71 106 141 176 211 246 281 316 351 t/d Fig. 3 The relation of EME and time (x=4m)

280 240 200 160

EME 120 80 40 0 1 39 77 115 153 191 229 267 305 343 t/d

Fig. 4 The relation of EME and time (x=5m)

4. Field experimental study on rheology electromagnetic radiation

KBD5 electromagnetic radiation instrument developed by China University of Mining and Technology has been used to test the change of electromagnetic radiation from the wall in # 2218 excavation roadway of Chengzhuang Coal Mine of Jincheng Coal Industry Group. Many monitoring points have been chosen and the test results are almost the same. This paper chooses one point and links the average values of electromagnetic radiation according to the order of time. The result is shown in Fig.5. It is known that the average values of electromagnetic radiation drop stepwise with the passage of time, which is because the data tested the same day, are almost the same but the data in the following days reduce in general. The data are the biggest on August 3, reduce gradually in the following days and to the lowest on September 2, so do other tested data of electromagnetic radiation from different depths on the drilling. The electromagnetic radiation field test, numerical simulation and theory analysis results are basically the same. XueXue Erlong Erlong et al. et /al Procedia / Procedia Engineering Engineering 26 00(2011) (2011 1571) 000 –– 1575000 15755

Fig.5 The relation (5m depth) EME strength and time of head-on tunnel

5. Conclusion

1) Based on the experiment of electromagnetic radiation due to the coal and rock deformation and fracture, combined with qualitative and quantitative, this paper introduces the constitutive equations based on the generalized original model of three-dimensional creep principal stress and the principal strain. 2) The heading roadway creep electromagnetic radiation in the process of coal and rock creep is simulated by FLAC3D software, and on the scene, the electromagnetic radiation is detected, which is basically the same as the theoretical analysis. 3) Theoretical analysis, numerical simulation and the field test results show that, the theoretical research results can be used to deal with the mine coal and rock deformation and the mechanics problems, such as permanent mining deformation and supporting of roadway, coal and gas outburst prevention. It provides a theory basis to effectively monitor coal and rock dynamic disasters.

References

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