Experimental investigation on mechanical behaviors and microstructure responses of the coking coal subjected to freeze-thaw cycles

Abstract

In this paper, the uniaxial compression test of coking coal with different freeze-thaw (F-T) cycles was carried out, accompanied by the monitoring of the acoustic emission (AE) system and digital image correlation (DIC) system. The results show that with the increase of F-T cycles, there is the continuous increase and obvious development of the sample mass and the pore structure respectively, causing the deterioration of mechanical properties. In addition, the AE activity of the samples gradually increased, which is more obvious in the compaction stage; furtherly, the tensile microcracks in the rock during the compression test always account for a larger proportion (except for 30 F-T cycles). For the failure characteristics, the rock sample changes from splitting tensile failure to shear failure, and the fracture surface morphology changes from rough to smooth. The damage constitutive model of coking coal subjected to the F-T effect and axial load was established, which is in good agreement with the experiment results. Finally, it is found that the initial damage of coking coal subjected to F-T cycles could be attributable to the expansion of pore and fissure space caused by the freeze of free water, the increasingly enhanced water-rock interaction and the interaction between mineral particles.

Keywords

coking coal / freeze-thaw effect / acoustic emission / microstructure / mechanical behaviors / damage constitutive model / damage mechanism

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