Structural control within flawed rock specimens under external loading as visualized through repeating nucleation on multiple sites by acoustic emission (AE)

SUMMARY The behaviour of discontinuities in rock mass have been experimentally investigated extensively for decades by a type of laboratory analogue of flawed rock specimens, taking the artificially prepared flaw(s) as the analogue of rock mass discontinuity(ies). The role of macroscale flaw(s) as controlling structure has been generally neglected. Here, we conduct detailed characterizations of the acoustic emission (AE) from the rock fracture process on the pre-flawed specimens under loading. Though the same phenomena from the literature can be reproduced within our tests, detailed spatial-temporal investigation on the AE events at the nucleation point suggests a different physical interpretation. Artificial flaw(s) play a non-negligible role as a controlling structure for the following rock fracture process including a series of nucleation points alteration via stress transfer. The interlocking parallelogram (IP) control and single-large-structural (SLS) control are two fundamental mechanisms initiated by the artificial flaws. Each of these two mechanisms are observed under a wide range of flaw settings and can potentially coexist within the across length scales. The scale-invariance feature is observed to be fundamentally different within the scale of specimens under SLS and/or IP control, suggesting the incompleteness at the specimen-scale for IP control. Therefore, no ‘fracture coalescence’ zone can be separately investigated without considering its external rock fracture evolution and confirming scale-invariance. Therefore, structural controlling mechanisms must be considered due to the pattern and AE characterization results.