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.
Highlights
A significant number of coal deposits are located in the northern regions of Russian Federation (Pechora, Taimyr, Zyriansky coal basins) and far away from the major consumers
Arrays of Vs and As values were obtained for each coal sample, along with the angle of h and numbers of F–T cycles
The authors investigated the patterns of polarized shear wave propagation in coal samples under cyclic F–T and came to the following conclusions: (1) The high sensitivity of the As parameter to the formation of cracks with a small opening was shown
Summary
A significant number of coal deposits are located in the northern regions of Russian Federation (Pechora, Taimyr, Zyriansky coal basins) and far away from the major consumers. While being transported through various climatic zones and stored under various conditions, is often exposed to cyclically changing thermal impacts in positive and negative temperature ranges. Such impacts lead to changes in the mechanical and consumer properties of coal. Since the middle of the last century, the scientific community has gained extensive experience in ascertaining the impact of temperature on the mechanical properties of rocks. In light of the aforementioned background, we consider the effect of cyclic freezing–thawing (F–T) operations on the properties of coals of various origins separately. The developed pore space, the crack systems of various orientations and the overall low initial strength make coal extremely sensitive to temperature changes. In Cai et al (2015, 2016) and Qin et al (2017a, b), the effect of cyclic
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