Compaction characteristics and permeability evolution characteristics of broken coal body under triaxial stress

In the process of coal mining, the compaction characteristics of the goaf and its permeability evolution characteristics are critical to the safe and efficient mining of coal mines, which directly affect surface subsidence, air leakage in the goaf and spontaneous combustion of coal. Although the stress and permeability of the goaf are very important, it is difficult to directly measure the stress and permeability of the goaf. Therefore, this paper uses the damaged coal and rock mass seepage test system to carry out the compaction and seepage tests of the broken coal mass under triaxial loading. The experimental shows that: (1) under the same stress, the strain of a single-size coal sample is smaller than the mixed particle size, and the porosity is greater than the mixed particle size. The larger the particle size of a single-size coal sample, the smaller its strain. (2) There are two stages of rapid compaction and slow compaction under the condition of triaxial compression of broken coal samples. The strain and permeability stress sensitivity of the rapid compaction stage are strong, while the slow compaction stage is weak. (3) Under triaxial loading of broken coal, permeability has an exponential relationship with effective stress, and a power function relationship with porosity, which obeys Darcy's law. The research results are of great significance for guiding the goaf gas drainage and preventing surface subsidence and spontaneous combustion of the goaf coal.