Study of triaxial compression mechanical properties and pore-fracture characteristics of coal rocks in the Yili Basin, Xinjiang

Compressive mechanical properties and pore-fissure characteristics of coal rock specimens from three stably developed coal seams M 1 , M 8 and M 12 in the Xinjiang Yili Basin were investigated in detail by a series of tests. The results show that the compressive mechanical properties of coal rocks in the Yili Basin are significantly affected by the confining pressure. The peak axial stress increases and the peak modulus of elasticity decreases as the confining pressure increases. The peak axial strain increases and then remains constant, while the peak circumferential strain and peak volumetric strain increase and then decrease. The confining pressure has almost no effect on Poisson’s ratio of the coal rock specimens. In addition, electron microscopy tests show that the microscopic fraction of the coal rock specimens is predominantly vitrinite, accounting for 83.1%-89.2%, while the percentage of the inertinite group is relatively small, at 10.3%-16.1%. The throat radius of the coal rock is mainly concentrated around 1-2 µ m, while the pore radius of the coal rock is between 150-200 µ m. The coal rock has an overall fine throat and low permeability, and the coal rock in the Yili Basin of Xinjiang is a typical low-permeability coal rock.