Rock damage and fracturing induced by high static stress and slightly dynamic disturbance with acoustic emission and digital image correlation techniques

A series of coupled static-dynamic loading tests is carried out in this study to understand the effect of slightly dynamic disturbance on the rocks under high static stress. The acoustic emission (AE) and digital image correlation (DIC) techniques are combined to quantitatively characterize the damage and fracturing behaviors of rocks. The effects of three influencing factors, i.e. initial static stress, disturbance amplitude, and disturbance frequency, on the damage and fracturing evolution are analyzed. The experimental results reveal the great differences in AE characteristics and fracturing behaviors of rocks under static loads and coupled static-dynamic loads. Both the Kaiser effect and Felicity effect are observed during the disturbance loading process. The crack initiation, stable and unstable propagation in the highly-stressed rocks can be triggered by cyclic disturbance loads, and more local tensile splitting cracks are found in the rocks subjected to coupled static-dynamic loads. The damage and fracturing evolution of rocks during cyclic disturbances can be divided into two stages, i.e. steady and accelerated stages, and the increase rate and proportion of each stage are greatly affected by these influencing factors. High initial static stress, low disturbance frequency, and high disturbance amplitude are considered to be adverse factors to the stability of the rocks, which would induce a high increase rate of the steady stage and a high proportion of the accelerated stage within the whole disturbance period. Based on the two-stage damage evolution trend, a linear-exponential damage model is employed to predict the instability of the rocks under coupled static-dynamic loads.