Experimental study of the surface potential characteristics of coal containing gas under different loading modes (uniaxial, cyclic and graded)

Abstract

In this paper, the characteristics and mechanism of the surface potential of coal containing gas for different loading modes (uniaxial compression, cyclic and graded loading) are investigated using an experimental surface potential testing system. Coal can produce a surface potential signal during gas adsorption. This signal increases with the adsorption time and exhibits a memory effect; that is, when the adsorbed gas pressure is increased, the surface potential increases. The coal containing gas can produce a surface potential signal based on different loading modes (uniaxial, cyclic, and graded loading), and the surface potential increases with the load. The higher the gas pressure is, the lower the peak stress is but the higher the maximum surface potential is. The surface potential under cyclic loading exhibits a significant memory effect and is lower than that during the stress-holding stage during graded loading. The surface potential caused by the loading and failure of coal containing gas is the result of the joint actions of gas and stress, which induce a free charge, a frictional force and an electrokinetic effect. This study offers theoretically significant and practical results that reflect the microscale process and electrical precursors of coal fracturing.