Study on a Coupling Model of Fracture Stress–Microseismic–Temperature of Composite Coal and Rock Deformation

To reveal the coupling relationship between stress, microseismic, and temperature during the deformation and fracture of composite coal and to further study the generation mechanism of deformation and fracture microseismic of composite coal-rock, the SMT (stress-microseismic-thermal) coupled model was derived based on the previously established SCT (stress-charge-thermal) coupled model. The top rock, coal, and bottom rock were extracted to prepare composite coal-rock specimens in the ratios of 1:1:1, 1:2:1, and 1:4:1 and pure coal. The uniaxial loading fracture experiments were carried out on the coal-rock specimens at four different loading rates of 0.1, 0.3, 0.4, and 0.5 mm/min. The variation laws of electromagnetic radiation, microseismic voltage, and temperature signals during the uniaxial loading deformation and fracture process of the composite coal-rock specimens were investigated. The experimental results show that the microseismic voltage and electromagnetic radiation signals are weak at the initial loading stage. The maximum values of the two signals appear when the stress achieves the peak point and the temperature drops on a slight slope. With the increase in the loading rate, the maximum peaks of the two signals decrease, where the change in microseismic voltage is more prominent. In the experiment of different coal-to-rock ratios at 0.5 mm/min, the electromagnetic radiation does not change much, and the peak value of the microseismic voltage signal is the largest in the sample with the coal-to-rock ratio of 1:2:1, followed by that of the pure coal sample. With the thickening of the coal seam, the top rock temperature drops more, indicating that the three signals have a strong consistency and precursor warning function. According to the experimental data, the relationship between the microseismic voltage energy and stress is fitted, and the results show that the two signals are in an excellent exponential relationship and that the fitting coefficient is above 0.9. Combined with the SCT coupling model, the relationship between electromagnetic radiation stress and microseismic voltage energy stress is substituted into the SCT model; then, the induced charge variable is eliminated. The stress-microseismic-temperature (SMT) coupling model is derived. The SMT model is used to fit samples f₁-f₁₂, and the coefficients <i>m</i> ₂ and <i>z</i> ₂ are equipped to verify the fitting. The coefficient of multiple determination <i>R</i> ² is generally above 0.9, indicating a higher accuracy compared with the SCT model. This suggests that the model has a strong fitting precision and provides a new approach for the prediction and forecasting methods of coal and rock dynamic disasters.