Experimental investigations of pressure stimulated currents from stressed sandstone used as precursors to rock fracture

Abstract

Precursor information of rock fracture is a prerequisite for rock dynamic disaster (RDD) prediction. To investigate the precursor information of rock fracture based on pressure stimulated current (PSC), progressive loading (PL) and step-like loading (SLL) experiments on sandstone samples were conducted. The response characteristics of PSCs from sandstone samples being actively loaded in the laboratory were analyzed and potential precursors to rock fracture based on PSCs are discussed. The results show that weak currents are generated instantaneously when a load is applied on sandstone samples and the PSCs correspond well to stress variations. In the PL experiments, the PSC responses are different in the different stages of deformation. In the compaction stage, the PSC first increases linearly and rapidly as the stress becomes greater but then decreases slowly a few seconds later; In the elastic stage, the current increases slowly and linearly with stress but it begins to rise with an increasing rate when the sample enters the plastic deformation stage, reaching the peak value of PSC the instant the final fracture occurs. In the SLL experiments, when stress is increased from a lower to a higher stress step, the PSCs increase rapidly and reach peak values the moment the stress stops increasing. In addition, the peak current increases exponentially with stress rate with a negative exponent. During stress maintenance, the PSCs decay slowly before finally reaching a stable value, and the PSC decaying process obeys the non-extensive statistical mechanics . The accumulated charge increases linearly with the relative stress, but the charge increasing rate are different in the three deformation stages. The variation rate of accumulated charge in plastic deformation stage is approximately eleven times as that in elastic deformation stage. The variation of current has a precursor response to rock fracture: the increase of PSC with an accelerative rate can be used as a precursor of rock failure during a progressive loading, the increasingly intensive abrupt drops during the PSCs decay are precursors for rock fracture during creep, and the rapid increase of accumulated charge variation rate can be used as a precursor of rock fracture both under progressive and step-like loadings. These research results are expected to provide new ideas and methods for RDD prediction.