JOURNAL OF COAL SCIENCE & ENGINEERING

(CHINA) DOI 10.1007/s12404-012-0105-0

pp 25–28 Vol.18 No.1 Mar. 2012

Rockburst hazard assessment based on electromagnetic emission in Xingfu Mine

XU Jia1, MA Feng-hai2, HAN Jun3 1. School of Geomatics, Liaoning Technical University, Fuxin 123000, China

2. Dalian University, Dalian 116622, China

3. College of Mining, Liaoning Technical University, Fuxin 123000, China

© The Editorial Office of Journal of Coal Science and Engineering (China) and Springer-Verlag Berlin Heidelberg 2012

Abstract In order to research the danger caused by the rockburst, the electromagnetic emission (EME) in the coal rock was

monitored and analyzed. The higher the stress in the coal is, the stronger the deformation and the failure are, and also the signal

of the EME will be. The EME is increased by a relatively large margin before the slight shock and rockburst break out at spot.

Therefore, some methods to monitor and forecast the danger of rockburst were proposed, including the critical point and devia-

tion values, which was by non-contract method. In the end, the observation of EME in Xingfu was used to analyze and forecast

the danger level by the rockburst. Then, the measures were proposed to prevent and cure the rockburst.

Keywords rockburst, EME, critical point, deviation value

Received: 6 September 2011 Tel: 86-418-3351992, E-mail: xuj_lntu@163.com

Introduction

Electromagnetic emission (EME) is generated in the coal rock when it breaks due to load. Researching EME provides a new way to understand the dynamic process and mechanism of the rockburst, which estab-lishes the basis for monitoring and forecasting the rockburst. The characteristics of EME have been ana-lyzed by Hexuqiu, Wangenyuan, etc., as well as the principle and the technique of forecasting the rock-burst using the EME (He and Liu, 1995; He et al., 1999; Dou et al., 2001; Wang et al., 2002). In China University of Mining and Technology, the research team has developed the EME detector of KBD5 and KBD7 and used them in forecasting the rockburst successfully (Qian et al., 2000; Dou and He, 2001; Wang et al., 2002; Wang et al., 2003).

EME technique is a geophysical method to forecast the dynamic disaster in the coal rocks such as rock-burst. The main parameters are the radiant intensity and pulse numbers to assess the dynamic disaster in the rockburst, coal, and gas burst. The intensity de-scribes the level of load and distortion. The pulse numbers describe the frequency of distortion and mi-crofracture in coal rocks. Using EME, the methods to monitor rockburst include critical values and deviation

methods. Due to the discrepancy in physical characteristics of

coal rocks and conditions of manufacture, the differ-ence is too large while using the critical value index to forecast the rockburst. In order to improve the fore-casting veracity, it is necessary to research the prog-nostic characteristics and its change law. In this paper, the four times statistics of the EME in the Xingfu Mine is analyzed to bring forward an assessment method and guidance for the prevention and cure of the rockburst (Dou and He, 2004).

1 General situation of rockburst in Xingfu Mine

Xingfu Mine is situated in the center of the Fuxin coal field and southwest to Haizhou open pit mine. The geophysical coordinate is 12141 east longitude and 4202 north latitude with an area of 3.22 km2.

It is up to 50 times that the rockburst has happened since 2000 and the distribution is shown in Fig.1. The rockburst will bring about critical danger to safe pro-duction. For example, the gas burst resulted in the rockburst in 3316 coal face that cause 214 victims in 2•14 extra serious accidents in 2005 (Li et al., 2005). The intensity and frequency of rockburst in Xingfu Mine increased year-by-year. Some characteristics

Journal of Coal Science & Engineering (China) 26

could be found according to these rockbursts in Ha-izhou Coal Mine. First, most of rockbursts locate in Gaode syncline, the main structure of Haizhou coal mine (Fig.2). This is obviously concentrative. Second, the damage of roadway after rockburst has the same characteristic, floor heave (Table 1). The magnitude of floor heave is 0.4 to 0.5 m and the maximum is 1.3 m. Some roadway’s roofs have unapparent subsidence.

Fig.1 Distribution of the rockburst in Xingfu Mine

Fig.2 Relation between rockburst and syncline

Table 1 Grades for danger level based on EME

Danger grades

Danger situation

Danger index

Measures for prevention and cure

A Safe <0.25 All work

B Slight danger

0.25~0.50 Strengthen the monitoring and forecasting of danger while mining

C Medium danger

0.50~0.75 Adopt measures to weaken intensity to cut down the dan-ger while working

D Strong danger

>0.75

Stop working and workers retreat. Take the measures to weaken the intensity and work after the danger pass away

2 Monitoring and analysis about elec-tro-magnetic radiation

2.1 Distribution of EME monitoring and the sta-

tistics Method of multiple-point monitoring method was

applied in Xingfu Mine. The monitoring points were set up at the gateroad bunker and return gateroad in coal face based on the geology condition and stopping art shown in Fig.3.

Fig.3 Survey point layout of EMR in panel 2312

There was 10 m apart 17 points. These points were monitored once every 2 days for 2 minutes by the KBD5 EME detector developed by China University of Mining and Technology.

2.2 Determination of the danger level The research shows that ( )t , ( )W t about coal

rock deformation is linear to the amplitude of EME and the pulse numbers. Danger level was determined in one of two ways.

(1) Index of amplitude of EME The function is as follows:

1

1

1

1 1

11 1

1 1

( ) 0 ( )

( ) ( )

( ) 1 ( )

E

E

E

E E a

E aE a E b

b aE E b

(1)

where, E1 is amplitude in 2 min; a and b are pa-rameters.

(2) Index of pulse numbers of EME The function is as follows:

2

2

2

2 2

22 2

2 2

( ) 0 ( )

( ) ( )

( ) 1 ( )

E

E

E

E E c

E cE c E d

d cE E d

(2)

where, E2 is the extra increment of pulse numbers every 10 seconds in 2 min; c and d are parameters.

2.3 Determination of discrimination model for

danger level At 11:25 p.m. on April 24, 2008, the destructive

rockburst happened in 2313 return airway. There is a 70 m bottom heave upwards from the opening and 1.0 to 1.4 m bottom heave in 30 to 40 m. The trap was damaged and there was 1 to 1.5 bottom heave in the range of 25 m from the opening of near -400 material channel.

On April 21, the maximum value of the EME was

XU Jia, et al. 2012, 18(1): 25-28 27

31.8 mV at the point 3. On April 23, that was the day before the rockburst generated, and the maximum was 75.1 mV. After it, the intensity of EME was 25.5 mV, which is shown in Fig.4. From this, it can be con-cluded that the intensity of electromagnetic radiation from the rockburst is 75 mV at least.

Fig.4 Contrasting curve for the intensity of EME before

and after the rockburst in return airway

On April 21, the maximum E2 of the frequency in-crement of the electromagnetic radiation in point 3 is 1 180. The value on date 23 is 110 and on date 25 is 107, which are shown in Fig.5.

Fig.5 Contrasting curve for E2 of the EME before and

after the rockburst in return airway

Besides, on September 26 and October 31, 2006, two rockbursts happened on area face, and on March 11, 2007, one rockburst happened. The intensities of the EME before the rockburst are 77, 83, and 75 mV, respectively (Fig.6).

Fig.6 Amplitude characteristics of EME while rockburst

Take the minimum of the EME as critical value, which is 75 mV. So, while E1=75,

1E =0.5, then a=0, b=150. From this, to Xingfu Mine, the criterion of danger level based on the intensity of EME from the rockburst is as follows:

1

1

1

1 1

11 1

1 1

( ) 0 ( 0)

( ) (0 150)75

( ) 1 ( 150)

E

E

E

E E

EE E

E E

(3)

In the same way, while 2E is 1 180, that is

20.5E , then c=0, d=2 360. So, the criterion of dan-

ger level based on frequency number of EME is as follows:

2

2

2

2 2

22 2

2 2

( ) 0 ( 0)

( ) (0 2 360)2 360

( ) 1 ( 2 360)

E

E

E

E E

EE E

E E

(4)

2.4 Determination of danger level for the rock-

burst Based on the cases given to the rockburst, the dan-

ger level caused by rockburst can be divided into five grades based on the EME method as shown in Table 1.

3 Conclusions

(1) There is obvious regularity for EME before and after the rockburst, that is, during the time before the rockburst, the amplitude and pulse number are large to a limit value. After the rockburst, the amplitude and pulse number will diminish.

(2) Based on the observations of EME before and after the rockburst in 2312, 3316, and 3311 workface, the model can be established to assess the danger level from the rockburst with fuzzy mathematics. This pro-vides guidance for the mine to take measures to pre-vent and cure the rockburst.

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