Abstract
Microseismic (MS) monitoring is an important and commonly used geophysical method in coal mines to predict rock burst which has great influence on safety production. MS monitoring technology and analysis method of the whole mine or working face have been matured, but its use in heading faces of coal mine is not mature due to small disturbances and narrow layout spaces. To carry out MS monitoring and early warning in the heading face, signal recognition must be adequately performed first, and monitoring objects and indicators must be obtained. Through field tests of MS systems at the 117 track gateway of Tengdong coal mine, interference signals of equipment operation and effective signals of coal vibration are accurately collected. After analysis, the waveform characteristics, spectrum, and propagation distance of the interference signals and coal vibration signal are different. Some effective signals with small energy (one-channel triggering) cannot be used as early warning indicators because they are concealed by interference signals. Through trial operation, it is found that large energy (three-channel and four-channel triggering) coal vibration events successfully predicted a rock burst. The MS system of 117 track gateway of Tengdong coal mine should be able to remove the interference signals in real time through the algorithm and take the number of large energy coal vibration signal rather than all coal vibration events as the predictor for rock burst risk monitoring.
Highlights
Waveform and Spectrum of Roofbolter Drilling Operation. e drilling operation of the roofbolter only affected the #1 sensor, showing that the propagation distance of the interference signal is greater than 15 m
Signal recognition is the primary task for monitoring and early warning of the MS system in 117 TGTC, and the interference signals should be recognized and removed in real time. erefore, a field test of signal recognition was carried out. e waveforms of interference signals and coal vibration (CV) signals are obtained. e interference signals include the roofbolter drilling operation signal, roofbolter compression bolt operation signal, belt conveyor working operation signal, and roadheader working process signal. e waveform characteristics, spectra, and propagation distances of the signals are analyzed. e results show that the waveform characteristics and main frequencies of the signals are different, and signal identification can be partly achieved by these features
The roadheader working interference signal has the largest maximum amplitude (MA) of 380 mV and the farthest propagation distance of more than 70 m. e MA of the CV signal obtained in the field test ranges from 238 mV to 7914 mV, showing some CV events smaller than the MA of the roadheader interference signal may be concealed
Summary
MS monitoring, as an important and commonly used geophysical method, has been applied in many fields, such as earthquakes [1,2,3,4,5], hydropower stations [6,7,8], metal mines [9,10,11,12], tunnels [13, 14], petroleum engineering projects [15, 16], hydraulic or pneumatic fracturing [17,18,19], and coal mines [20,21,22,23]. Among these fields, coal mines are more widely monitored by MS systems. In the field of rock burst monitoring, monitoring technology and analysis method of working face have been matured, but research on MS monitoring in heading faces is not mature due to small disturbances and narrow layout spaces. (2) MS monitoring is the main technology of early warning of rock burst in coal mine, but it has not been used in early warning of rock burst in heading face. It is difficult to deploy measurement points in space due to the single heading of the gateway, so four sensors are arranged in a straight line and installed to the tail of the roof rebar bolt of 117 TGTC. After arrangement of the MS system is finished, the bottom noise waveform of the MS system is tested first, and the precise running time of various equipment and occurrence time of CV (CV signals are recorded by sound that emits at the same time) is recorded in detail. e running records of the equipment mainly include drilling operation of the roofbolter, compressing blot operation of the roofbolter, running time of the belt conveyor, and running time of the roadheader
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