Search

In order to give an accurate warning of coal and gas outburst disaster, a triaxial compression wave velocity test system of coal and rock with gas outburst was built. The coupling relationship between the axial pressure, confining pressure, the gas pressure and wave velocity of coal and rock with gas was studied under the laboratory conditions, and the mathematical model of wave velocity and pressure was established. The results show that: when the load of the sample is constant, with the increase of the gas pressure, the longitudinal wave velocity will decrease sharply at the beginning, and then tend to be stable, showing a linear negative correlation; when the confining pressure and the air pressure conditions are constant, the wave velocity of the sample will increase rapidly after the axial pressure is applied at the beginning, and then the wave velocity tends to be flat and increases linearly, showing an exponential function relationship; when the air pressure and the confining pressure strip, with the increase of confining pressure, the longitudinal velocity of the specimen increases uniformly and linearly, and the mathematical model fitted by the three test results has a high correlation coefficient.

The analysis of time-domain characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) signals in process of rock failure under load mostly draws qualitative conclusions from amplitude, ringing count, energy and other parameters, without directly giving time-domain correlation of AE and EMR signals, and parameters used in frequency-domain characteristics analysis of AE and EMR signals are relatively simple. In view of the above problems, monitoring experiment of AE and EMR signals of rock samples under uniaxial compression was carried out, and time-frequency characteristics of AE and EMR signals in different stages of rock failure under load were analyzed. The results show that: ① In compressionstage and elastic stage, amplitude of AE and EMR signals is basically zero. In accelerated failure stage, amplitude of AE and EMR signals increases gradually and the number of signals increases gradually. In stage of complete failure, amplitude of AE and EMR signals increases and decreases almost at the same time. When load reaches the peak value, amplitude of AE and EMR signals reaches the maximum at the same time. Amplitude of AE signal is larger than that of EMR signal in the whole process of failure under load. ② In accelerated failure stage, AE and EMR signals are significantly correlated. In stage of complete destruction, AE and EMR signals are highly correlated. In the whole process of failure underload, variation trend of AE and EMR signals with time is basically the same, and AE and EMR signals are highly correlated in time-domain. ③ In accelerated failure stage and complete failure stage, EMR signals are mainly low frequency and very low frequency signals. Compared with EMR signal, AE signal has wider frequency band and larger amplitude of main frequency. Main frequency concentration range of AE and EMR signals is similar but not completely consistent. Amplitude of main frequency of AE and EMR signals in complete failure stage is larger than that in accelerated failure stage.

Economically, Northeast Asia is the most dynamic place in the world, but the security situation in the region is dire and precarious. Even though cooperation and rivalry have long coexisted there, recently the latter has been overshadowing the former as three sets of rivalries have come to haunt this region collectively. In addition to the decades-old inter-Korean rivalry, the old Sino-Japanese rivalry has been revived, and the rivalry between China and the U.S., a perennial phenomenon, has also come to take center stage in Northeast Asia. Although the three sets of rivalries have their own unique causes and ramifications, they have close connections. Among all the conflicts and confrontations, the Sino-U.S. rivalry is now playing a defining role. Given the lack of mutual trust, absence of inclusive regional security institutions, unaddressed historical grievances, and unfulfilled leadership aspirations, the three set of rivalries will not go away in the foreseeable future and might reinforce each other to make the Korean Peninsula and Northeast Asia the most volatile and dangerous place on earth. [ABSTRACT FROM AUTHOR]