Experimental study of coal fracture dynamics under the influence of cyclic freezing–thawing using shear elastic waves

Abstract

Cyclic freezing–thawing can lead to fracture development in coal, affecting its mechanical and consumer properties. To study crack formations in coal, an ultrasonic sounding method using shear polarized waves was proposed. Samples of three coal types (anthracite, lignite and hard coal) were tested. The research results show that, in contrast to the shear wave velocity, the shear wave amplitude is extremely sensitive to the formation of new cracks at the early stages of cyclic freezing–thawing. Tests also show an inverse correlation between coal compressive strength and its tendency to form cracks under temperature impacts; shear wave attenuation increases more sharply in high-rank coals after the first freezing cycle. Spectral analysis of the received signals also confirmed significant crack formation in anthracite after the first freeze–thaw cycle. The initial anisotropy was determined, and its decrease with an increase in the number of freeze–thaw cycles was shown. The data obtained forms an experimental basis for the development of new approaches to preserve coal consumer properties during storage and transportation under severe natural and climatic conditions.