A Study of the Effect of Freeze–Thawing by Liquid Nitrogen on the Mechanical and Seepage Characteristics of Coal with Different Moisture Content Values

In order to study the effect of freezing and thawing liquid nitrogen on mechanical seepage characteristics coal rock with different water content values, conventional triaxial loading tests freeze–thawed samples values were carried out using non-contact digital image processing technology. The research results showed that same content, peak strength a sample was smaller than non-freeze–thawed sample, Poisson’s ratio larger sample; compared strain fluctuation concentration in stages compression density, elasticity, yield, damage weakened after freeze–thawing by nitrogen, but local stress more obvious; mainly single shear damage, fissures inclined small openings. higher obvious tensile damage; increase permeability linear decreasing trend, 0.03 × 10–3 μm2 when reached 9%. non-linear increasing under expansion, faster growth rate; could reach 6.30 can provide theoretical guidance for gas permeation enhancement deep low-permeability seams.