The pressure-stimulated rock current (PSRC) is an extremely important petrophysical phenomenon and the catastrophic characterization of solid Earth, which attributed to several physical mechanisms including dislocation and positive holes (Ph). The micro-crack development coupling with the two mechanisms runs through the whole process of loading rock to failure, but how its development and type affect PSRC has not been well studied so far. The acoustic emissions (AE) and PSRC between the loaded part and free part were detected synchronously when bi-axially load dried diorite specimens to failure. This study revealed the remarkable characteristics of staged-variation of PSRC: a low-stable fluctuation in the elastic stage, accompanied with an instantaneous step-rising of average 26.6 nA; then exhibited stead fluctuation at the step until failure, accompanied with a negative pulse of several hundred nanoampere. The little PSRC in the elastic stage was mainly attributed to the Ph activated by tensile micro-cracks; while the step-rising large PSRC was attributed to the sudden rising of number and ratio of shear micro-crack at the moment of elastoplastic transition; after that, the PSRC was generated mainly by the coupling of continuous massive Ph activation and dislocation sliding resulting from shear micro-cracks. A quantitative expression was established to describe the PSRC dynamics. The results enriched and refined the mechanisms of PSRC, which provide key basis for engineering rock mass monitoring and critical status scrutinizing, and are of reference meanings for the monitoring of seismic electrical, magnetic and related radiation as well as the identification of earthquake precursors.

The variations in the electric property of loaded rocks are essential in understanding the rock dynamics and fracturing process. Decades of laboratory experiments have revealed different behaviors of stress-stimulated electric current due to the effects of rock types, loading modes, and detection methods. These different behaviors result in difficulties in revealing the underlying physics of electric current in rock and explaining adequately the wide variety of electric precursors measured before rock failure or geohazards. In this study, cubic- and conical-shaped diorite specimens were specially designed and produced to investigate experimentally the characteristics of pressure-stimulated rock current (PSRC) in the process of loading rock specimen to failure. We measured a particular phenomenon of diorite PSRC variation with pressure, that is, PSRC remained nearly stable until the applied stress reached 83%–98% of the failure strength. A remarkable step-like increment in PSRC was uncovered, and drastic oscillations with maximum amplitudes of several hundreds of nA happened one second prior to abrupt rock failure. A holistic mechanism that includes positive hole activation, field emission of electrons due to crack charge separation, and moving charged dislocation was applied to interpret this particular phenomenon. We found that these mechanisms contribute comprehensively rather than individually to the evolution of PSRC. We expect to provide an improved understanding of the underlying physics of PSRC and the variation in rock electric property.