Acoustic emission and fractal characteristics of red beds soft rock under water-force coupling

• Published in: Scientific reports 2024-02, Vol.14 (1), p.4424-19, Article 4424
• Main Authors: Chen, Lei, Liu, Taiyu, Jia, Baoxin, Tang, Jupeng, Liu, Jiashun
• Format: Article
• Language: English
• Subjects: 639/166; 639/166/986; Acoustic emission; Correlation coefficient; Cracks; Deformation; Excavation; Fractal characteristics; Fractals; Groundwater; Humanities and Social Sciences; Immersion; Mechanical properties; multidisciplinary; Red beds soft rock; Rocks; Scanning electron microscopy; Science; Science (multidisciplinary); SEM; Tunnel engineering; Uniaxial graded loading; Water content
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-024-54814-2

Groundwater has a significant influence on the mechanical properties of surrounding rock. Aiming at the large deformation of surrounding rock of red layer soft rock tunnel affected by groundwater, the uniaxial graded loading tests were carried out on red beds soft rock with different water content. The failure process of the specimen was monitored by acoustic emission (AE) and the crack evolution law was analyzed, and the scanning electron microscopy (SEM) was used to compare the microstructure of the specimens before and after immersion. Combined with fractal theory, the monofractal and multifractal characteristics of AE ringing count during the loading process of red beds soft rock were analyzed. The results show that, with the gradual increase of water content, the AE ringing count before the yield stage gradually decreased, and the corresponding cumulative ringing count at the same time gradually decreased, and the decrease was large in the early stage of immersion, and decreased in the later stage. The cumulative ringing curve gradually slowed down, the internal crack appeared earlier, the cumulative ringing curve stepped significantly, the AE signal amplitude gradually weakened, and the bandwidth of each frequency band gradually decreased. The failure of red beds soft rock with different water content is dominated by shear crack, and with the gradual increase of water content, the proportion of shear crack increases gradually, and the AE b value decreases gradually. With the gradual increase of the relative peak strength, the correlation dimension D of red beds soft rock with different water content increases first and then decreases. At 80% of the relative peak strength, the correlation dimension D reaches its maximum value and then drops sharply until it is maintained at a relatively low level, and the correlation dimension D gradually decreases with the water content. The fitting correlation coefficients of different water content (ln C ( r ), ln r ) are all above 0.9, indicating that the AE ringing count of water-bearing red beds soft rock has fractal characteristics, and the higher the correlation coefficient, the higher the self-similarity of AE ringing count sequence. As the weight q gradually increases, the generalized fractal dimension D ( q ) gradually decreases. When q  ≠ 0, under the condition of the same q , D ( q ) presents a trend of first increasing and then decreasing. The multifractal characteristics of AE ringing count of red beds