Experimental substantiation of acoustic method for determination of “coal bed - country rock” contact relations based on boundary inverse problem solution

The article describes the acoustic method developed by the authors to determine the contact conditions between coal seam and host rocks on the basis of boundary inverse problem solution. Justification of the applicability of the method is made by means of physical modeling, in which samples from the model material were subjected to step-by-step uniaxial loading with simultaneous ultrasonic sounding using a multichannel scheme. In this case, various friction conditions were set for different samples at the “sample-plate of the press” interface. Based on the results of sounding, the distribution of velocities in the illuminated domain of the sample was reconstructed using tomographic processing. The array of data obtained as a result of acoustic tomography was used as input data to solve the inverse problem. As a result of the solution of the inverse problem, it was shown that the appearance of slip regions at the boundaries of the sample generates tensile stresses, the magnitude of which reaches 0.8 from the axial load. The developed method makes it possible, on the basis of acoustic measurements, to identify areas with a reduced coefficient of friction between the coal seam and the host rocks, the presence of which may be the reason of dangerous dynamic phenomena.