Test and analysis of mechanics and permeation properties of raw coal

Abstract

In this paper, we investigated the mechanics and permeation properties of the raw coal sample during loading and unloading process, and come to some conclusions: the permeability of the sample increases nonlinearly during the unloading confining pressure process. The larger the gas pressure is, the greater the increase range of the permeability will be. The larger the confining pressure unloading amplitude is, the greater the increase range of the permeability will be. In the loading process, the permeability and the axial strain of the specimen change in a “V” shape. As the gas pressure increases, the peak strength of the specimen gradually decreases, and fitted the gas pressure and the peak strength are accordance with the linear relationship. As the confining pressure increase, the peak strength of the sample gradually increases, and fitted the confining pressure and the peak strength are accordance with the exponential function. The internal friction angle of the coal sample was 43.22°, and the cohesion was 3.77 MPa. The relationship between the fitted gas pressure and internal friction angle, gas pressure and cohesion is in line with linear functions. Maintain an axial stress constant, unloaded confining pressure to a constant state of target value, the permeability of specimen shows a constant pressure boosting flow zone, the relationship between permeability and deviatoric stress is accordance with the ExpDec1 function during the process of unloading confining pressure and prepeak loading axial stress.

Investigation of the evolution of damage and permeability of coal containing gas based on acoustic emission characteristics

“…[17][18][19] In order to describe the change law of the coal seam permeability, the relationship between macroscopic mechanical properties (such as deviation stress, effective stress, and fracture volume) and the permeability of damaged coal was established based on test data . [20][21][22][23] The macroscopic mechanics and gas permeability of the coal were mainly studied. However, due to the limitations of testing equipment, the mechanical mechanism for coal damage evolution and its effect on gas permeability were rarely studied.…”