Experimental investigation on mixed mode I-III fracture characteristics of sandstone corroded by periodic acid solution

Abstract

To explore the deterioration response of rock engineering structure under seasonal acid rain, a large number of mixed mode I-III fracture experiments were conducted on sandstone with the edge notched disc bending (ENDB) specimens. Before fracture tests, all the sandstone samples were respectively subjected to 0, 2, 4, 7 and 10 wetting–drying cycles with hydrochloric acid solution to simulate the periodic acid rain corrosion. In addition, the deterioration mechanism was revealed by chemical analysis and observing the variation in microstructure characteristics of the sandstone specimens with the scanning electron microscope (SEM). The results showed that the mixed mode I-III fracture toughness components (i.e. KIf, KIIIf) and effective fracture toughness (i.e. Keff) decreased gradually with increasing wetting–drying cycles. And the larger the loading angle or closer to the mode III, the greater deterioration degree of effective fracture toughness. Besides, the influence of periodic corrosion had an obvious time sensibility. All of these fracture parameters decreased greatly at the early stage of the cyclic procedure, and then, the rate gradually tended to be flat with the increase of the wetting–drying cycles. Moreover, the surface of the sandstone specimen became rougher, even multiple micro-cracks and holes were initiated after undergoing periodic acid corrosion. Macroscopically, it led to the decrease of its ability to resist fracture. The degradation effect could be attributed to the accumulation and coupling of multiple physical and chemical water–rock interactions.