Weak current phenomenon in stressed coal and its prospective applications in early warning for coal and rock dynamic disasters

Abstract

In this study, some loading experiments were conducted on coal specimens using the established weak current testing system to investigate the effects of weak currents in coals. The response characteristics of weak currents during the coal deformation process were analyzed, and a quantitative relationship between weak currents and the mechanical behaviors of coal was established. The principles for predicting coal and rock dynamic disasters based on the weak current method were proposed. Furthermore, drawing upon the results obtained from on-site practical applications, a forward-looking assessment of the potential applications of this methodology is presented. The results indicate that the deformation of loaded coal generates weak currents. The fluctuations in these weak currents exhibit a notable alignment with variations in stress, with the magnitude closely tied to the coal mechanical characteristics like stress, strain, and strain rate. Notably, in the compaction and plastic deformation stages, the weak current rises in tandem with the strain rate, while in the elastic deformation stage, the weak current exhibits a linear increase in correlation with stress and strain. Under perturbation loading, the coal produces some periodic weak currents, referred to as the pulsating direct current (PDC). And the variations in the PDC align with stress changes. Furthermore, the weak current demonstrates a reliable precursor response to coal damage, with some unusual fluctuations observed during the accelerated increase process (plastic deformation stage) serving as the precursor indicators for the progressive failure of coal. Conversely, the pulse-like fluctuations observed during the attenuation process can be regarded as the precursor features for the coal's creep failure. The phenomenon of weak currents in stressed coal serves as a pivotal foundation for conducting weak current measurements in mines. The intimate correlation between weak currents and the mechanical behaviors of coal underscores a crucial prerequisite for employing the weak current technology in monitoring stress within coal and rock formations. Furthermore, the discernible precursor response of weak currents to coal damage provides a vital assurance for predicting coal and rock dynamic disasters through the utilization of weak current technology. The weak current technology possesses some advantages such as high responsiveness, clear precursor signals, and robust anti-interference capabilities. These attributes make it highly promising for some applications in the stress monitoring within coal/rock mass and the early warning for coal and rock dynamic disasters. In the future, some further researches on the fundamental theory and applied technology of weak current in stressed coal and rock are needed to provide a support for the development of precise spatiotemporal monitoring and early warning of coal rock dynamic disasters using the weak current methods.

Keywords

• stressed coal
• weak current
• mechanical behavior
• precursor response
• monitoring and early warning