Visualized characterization of damagein granite-shotcrete beams based on acoustic emission

Abstract

To study the synergistic flexural damage resistance characteristics of the surrounding rock-shotcrete lining structure of water transportation tunnel, two granite-shotcrete composite beams were prepared for four-point bending tests with different loading rates. The four-point bending tests of the granite-shotcrete composite beams were monitored by two nondestructive monitoring techniques: digital image correlation (DIC) and acoustic emission (AE). Results show that when the crack extended from the shotcrete to the granite surface, the load-strain curve showed an obvious inflection point in the post-peak descending section, which can be a sign of granite crack initiation. Through identifying the damage types in shotcrete by AE technology, we found that the proportion of shear damage increased with the increase in strain rate. For the visual analysis of the internal damage of the composite beam, the spatial b-value was calculated using the acoustic emission damage localization data. Then, a new Rb-value was constructed by attaching coefficients to the spatial b-value in combination with the density distribution law of damage localization in space. Compared with the spatial b-value, the cloud map of Rb-value had a higher differentiation of different damage degrees, which improved the visualization of damage. Finally, the damage clouds localized by Rb-values were compared with the crack clouds monitored by DIC, which verified the effectiveness of the proposed method for damage visualization using AE technology.