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Compared with the energy dissipation of coal and rock failure, the more intuitive stress drop has certain practical significance for assisting the study of coal and rock failure characteristics and variation law of geophysical signals. And the stress drop is the macroscopic manifestation of energy dissipation. Most of the current research on energy dissipation and stress drop is only for one-sided research, without a comprehensive study on the relationship between the two. The relationship between the two is not clear, which restricts the application of the stress drop index. In order to solve the above problems, YAW−600 microcomputer controlled electro-hydraulic servo pressure testing machine is used to carry out uniaxial compression experiments on coal samples. The evolution characteristics of energy dissipation index and stress drop index in the whole process of coal sample failure under load and the relationship between them are studied and analyzed. Based on theoretical analysis, the relationship between energy dissipation index and the product of stress level and stress drop index is further studied. The results show that the energy dissipation index and stress drop index in the uniaxial compression failure process of coal sample have good response to the significant fracture of coal sample. And the indexes are in the same order of magnitude in numerical value, but they are not completely proportional. The energy dissipation rate is linearly related to the product of stress level and stress drop rate. And the energy dissipation is linearly related to the product of stress level and stress drop. The goodness of fit is 1 and 0.997 5 respectively. Compared with the energy dissipation index, the more intuitive product of stress level and stress drop index is more sensitive to the significant damage of coal samples, and has a burst characteristic. The research results clarify the relationship between energy dissipation and stress drop, and provide a certain theoretical support for the application of stress drop index. The relationship can be used for in-depth research on the coal rock failure characteristics and the variation law of geophysical signals such as acoustic emission, electromagnetic radiation and infrared radiation.

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.

In order to prevent danger of coal and gas outburst in process of rock cross-cut coal uncovering, tests and analysis on acoustic emission in rock cross-cut coal uncovering process in a coal mine were conducted based on acoustic emission monitoring system. The analysis and research results indicates that acoustic emission intensity increases rapidly in 2-3 hours before jet orifice occurred, peak strength can reach 2-3 times higher than that no outburst danger, then dropped to lower level before jet orifice occurred. The more serious the jet orifice was, the higher the intensity of acoustic emission was. The variation range of the acoustic emission intensity could reflect severity of the jet orifice, the more obvious the jet orifice was, the more severe the changes of gas concentration was, the greater the growth rate of coal and rock acoustic emission intensity was and the higher the peak intensity was. The analysis and research results have important reference significance for monitoring and forecasting of coal outburst risk in rock cross-cut coal uncovering.

Uniaxial compression test was conducted on concrete samples, and change characteristics of infrared radiation and acoustic emission of the samples in loading process were tested and studied by use of infrared imager and acoustic emission instrument. The research results show that infrared radiation temperature curve presents decreasing firstly and then increasing in the loaded concrete samples failure process, and temperature increasing amplitude of average infrared radiation temperature and the maximum infrared radiation temperature are respectively 0.15 ℃ and 1.05 ℃ when the samples failure. Before the samples failure, the average infrared radiation temperature has obvious precursor information that the temperature quickly drops at 66.7% load ratio and rises at 82.6% load ratio. During stage of the concrete samples fracture and its development, low and high temperature bands appear on infrared images, the high temperature bands appear in friction area of two fracture surfaces, as well as the low temperature bands are corresponding with sample cracks which are in tension fracture zone. Infrared radiation evolution characteristics of concrete deformation and failure provide a new method for concrete engineering destruction monitoring.

A multisignal nanosecond synchronous acquisition system to measure acoustic emission (AE) and electromagnetic radiation (EMR) generated during the process of loading and failure of coal and rock samples is established. The correlation between the energy of the AE and EMR signals and the loading stress of outburst coal-rock samples was studied, and the characteristics of the AE and EMR signals during the process of loading and fracturing the outburst coal and rock samples were analyzed. The results show that (1) before the failure of the outburst coal and rock samples, the fluctuation of the AE and EMR signals is the largest, with the same rising and falling trend, and the intensity is not strictly positively correlated, with the phenomenon of low EMR when the AE intensity is high; (2) the EMR and AE deviation degree and frequency exhibit a good response to coal and rock fracturing. The correlation between EMR and stress drop is stronger than that of AE, and the AE signal is richer than the EMR signal. The results show that it is feasible to develop combined AE and EMR early warning technology to improve the early forecasting accuracy of coal and gas outbursts. [ABSTRACT FROM AUTHOR]

Summary: The process of building rock failure is often accompanied by stress drop and energy release, which seriously threaten the safety of building structures. To reveal the law of energy release and transformation in the process of rock stress drop and establish a rock structural health monitoring index based on stress drop energy, the relationship between the stress drop and acoustic‐electrical (acoustic emission and electromagnetic radiation) energy of the shale and limestone failure process is studied in this paper. The results show that, in the early stage of rock loading, there is almost no stress drop dissipated energy, and the change in acoustic‐electric signals is not obvious. In contrast, in the later stage of deformation and failure of rock, the generation process of stress drop is accompanied by significant stress drop dissipated energy and acoustic‐electric energy release. With the increase in stress drop dissipated energy, the released acoustic‐electric energy gradually increases, and there is a good linear positive correlation. The release mechanism of the acoustic‐electric energy in the process of stress drop is mainly related to the crack propagation effect. The more significant the stress drop is, the faster the crack unstable propagation, the more intense the charging and discharging processes are on the crack faces, and the more acoustic‐electrical energy is released. Finally, a new indicator of rock structure health monitoring based on stress drop energy is established by a statistical method, and the health status of the rock mass structure is divided into weak, medium and strong danger, thus reflecting the stress distribution state and structural stability of rock. [ABSTRACT FROM AUTHOR]

• HHT method can well process and analyze the EMR waveform signal of coal failure. • The EMR parameters extracted by HHT improve the identification of coal failure. • Compared with STFT and WT, HHT has more advantages in processing EMR waveform. Electromagnetic radiation (EMR) waveforms contain rich information on coal fracture law, which is of great value to the refined study of their characteristics. In this paper, the Hilbert-Huang transform (HHT) method is used to analyze and process EMR waveform of coal failure process. The results show that HHT method can adapt well to the nonstationary and nonlinear characteristics of EMR waveform. It adaptively decomposes EMR waveforms by empirical mode decomposition (EMD), extracts the intrinsic mode function (IMF) characteristics of EMR waveforms, and obtains the law of instantaneous energy changes of EMR waveforms. At the same time, EMR waveform energy is quantitatively expressed on the three-dimensional Hilbert energy spectrum (time–frequency-energy distribution), and the refined features of EMR waveform signal are effectively extracted. The instantaneous energy of EMR and the three-dimensional Hilbert energy spectrum processed by HHT method more easily describe the fracture law of coal body. Compared with conventional characteristic parameters, such as EMR amplitude and dominant frequency, the identification degree of the precursor characteristics of coal body instability is greatly improved. Among the short-term Fourier transform (STFT), wavelet transform (WT) and HHT nonstationary signal processing methods, HHT method has an improved adaptability and superiority and can reveal the characteristics of coal deformation and failure more carefully and accurately, which provides a new means for better using and improving EMR method to monitor coal instability and failure. [ABSTRACT FROM AUTHOR]