Experimental study on freeze-thaw damage and seepage characteristics of coal rock at different prefabrication temperatures

Abstract

This experimental study probes into the evolution patterns of fine damage and mechanical and seepage characteristics of coal rocks using the coal rock triaxial servo experiment system by employing three types of pretreatment methods, namely heating, freeze-thawing with liquid nitrogen and freeze-thawing with water, with an aim to investigate the effect of temperature on freeze-thaw damage and seepage characteristics of coal rocks.Results show that higher preheating temperature leads to more severe structural damage, damage to water-filled liquid nitrogen freeze-thawed coal samples at the same temperature is greater than that of liquid nitrogen freeze-thawed coal samples and heated coal samples only, the degree of damage is negatively correlated with the wave speed and positively correlated with the number of joint dimensions of the end face damage; coal samples with high triaxial compressive strength feature low pre-deformation under different pretreatment methods; all three pre-treatment methods lead to an increase in the number of internal pores and fractures in the coal sample, resulting in the formation of a network of fractures.Freezing and thawing the coal sample with warmed water and liquid nitrogen demonstrate more stronger effect than that of freezing and thawing with warmed liquid nitrogen only.Therefore, in engineering practice, preheating-water injection-liquid nitrogen injection freeze-thaw could be employed to achieve efficient coal seam penetration and improve the effect of gas extraction.

Keywords

• liquid nitrogen freezing and thawing
• triaxial loading
• a closer look damage
• seepage
• translucency