Study on the evolution of pore structure and desorption characteristics of crushed tectonic coals under the different conditions of unloading confining pressure

Rapid pressure relief has an important influence on the continuous development of coal and gas outbursts. The particle size distribution of crushed tectonic coals under the different conditions of unloading confining pressure were analyzed together with the pore structure and desorption characteristics. The overall pore volume and desorption of the crushed tectonic coals were estimated. The results show that the increase of the unloading speed of confining pressure will aggravate the damage of the tectonic coals. With the increase of unloading speed of confining pressure from 0.01 MPa/s to 0.1 MPa/s, the volume of micropore, macropore, and total pore increased by 8.04%-10.62%, 6.92%-8.38%, 7.41%-9.40%, respectively; the gas desorption (in 120 min) increased by 20.56%-25.09% (equilibrium pressure was 0.74 MPa), respectively. This implied that under the rapid pressure relief condition, the damage of tectonic coal, pore structure evolution and unsteady gas gush provided favorable conditions for the continuous development of outbursts.