31 / 2021-06-25 15:17:35

"Silent period" precursor characteristics of AE-EMR signals before coal and rock failure

coal and rock failure; AE-EMR responses; damage evolution; silent period; rock burst

The cause factors of rock burst are complex and the early warning is difficult. There is a phenomenon of missing early warning when only high critical value is used for early warning of rock burst. In response to above phenomena, in this paper, based on the study of acoustic emission (AE)-electromagnetic radiation (EMR) response characteristics during uniaxial loading at laboratory specimen scale, damage parameter evolution law, and the evolution law of microseismic (MS)-AE-EMR precursor characteristics prior to rock burst occurrence in large-scale coal and rock mass, a "silent period" phenomenon contrary to the high critical value early warning principle has been found. Research results show that before the load reaches the peak stress, the AE and EMR signals present a "silent period" phenomenon, the response characteristics of "silent period" can be used as one of the precursors to warn the imminent failure of coal and rock specimens. Before the occurrence of rock burst, the abnormally increase of MS-AE-EMR signals and are accompanied by the “silent period” phenomenon, which can be used as a precursor to the risk of rock burst. The MS events in the "silent period" decreased by about 57~88% compared with those in the abnormal increase stage. The internal damage evolution process of coal and rock can be divided into four stages. The change rate of damage parameter before and after point B (generally corresponds to 85~90% of the peak stress) in the AB stage is almost zero, which is the cause of the "silent period" phenomenon. The phenomenon of the “silent period” of the AE-EMR signals during the loading process of coal and rock specimens provide a theoretical foundation for the rock burst warning based on the precursor characteristics of the "silent period" of monitoring parameters of MS-AE-EMR monitoring system, which effectively complements the existing monitoring and early warning methods. The "silent period" precursor characteristics realizes the early warning of rock burst in "silent period", where without abnormal increase of monitoring parameters before rock burst.