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.

Experimental Study on Gas Seepage Characteristics of Axially Unloaded Coal under Different Confining Pressures and Gas Pressures

“…Specifically, GPs with a constant pressure difference were applied at both ends of the coal sample, so that a certain pressure gradient was maintained in the coal sample to promote gas flow through the coal fractures; meanwhile, the quantity of gas flowing through the coal sample was measured. When the flow in the coal sample stabilized to form a steady flow, the quantity of gas flowing through the coal sample in the time period was recorded, and the permeability was calculated, using the control Equation (1) [5]:…”

“…To prevent and control gas accidents in a safe, economical and effective way, scholars have carried out extensive experimental and theoretical research, and put forward effective prevention and control measures. Among them, the technology of protective coal seam mining is an effective method that was put into practice [5][6][7][8][9]. The stress states of the coal seams differ.…”

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.…”