Comparative Study on Mechanical and Permeability Characteristics of Raw Coal and Briquettes under Different Loading Rates

Taking raw coal and briquette samples as research objects, the seepage test was carried out in the process of triaxial compression deformation, and the mechanical seepage characteristics of coal samples under different loading rates were studied. The results show that the loading rate has a great influence on the elastic modulus of the raw coal, while the elastic modulus of the briquette has a small change,moreover, with the increase of the loading rate, the peak stress of the raw coal and briquette increases first and then decreases; in the destruction stage, the destruction of briquette shows ductility characteristics, while the destruction of raw coal is sudden, which is closer to the destruction process of coal and gas outburst on site; at the same loading rate, although the permeability of both briquette and raw coal decreases first and then increases with the increase of stress, the permeability of briquette decreases more than that of raw coal in the early stage, and the briquette is in the form of shear slip failure, the post-peak permeability is lower than the initial permeability, while the raw coal is in the form of shear and tension failure, and the post-peak permeability increases sharply; with the increase of loading rate, the permeability of coal sample shows a more obvious "V" pattern.