Characteristics of self-potential of coal samples under uniaxial compression

Abstract

Deformation and fracture of a coal body under load may cause potential changes. Using coal samples under uniaxial compression, the coupling relationships between coal mass potential (surface potential) and stress during a complete stress–strain process were determined. Based on the potential difference of coal samples during loading rupture, the time–space evolution signatures of the electrical potential and stress of bituminous and anthracitic coal samples under load during a complete stress–strain process were dynamically depicted with high precision. Experimental results demonstrated that the parameters of self-potential and stress of these coals showed consistent variation with change of uniaxial loading pressure. During the initial stage of uniaxial compression (crack closure and elastic deformation), the self-potential difference of bituminous and anthracitic coals showed a linear increase or decrease with increasing uniaxial pressure, with average rates of change of 0.3565 mV/MPa and 1.1128 mV/MPa, respectively. With a gradual increase of uniaxial loading pressure (into the softening stage), the catastrophic points of uniaxial loading pressure corresponded to the inflection points of the self-potential change. The magnitude of the changes in the self-potentials of both bituminous and anthracitic coals was 10–100 mV before and after the last inflection points. The surface potential distribution of coal samples during uniaxial loading was well described by the self-potential profile, which indicated the degree of damage to the sample. The self-potential of a coal sample caused by deformation and fracture can therefore be used to evaluate the stress state of the coal mass. This work provides a theoretical foundation for application to a method for early prediction of coal and rock dynamic disasters.