Cyclic Behavior of Fiber-Reinforced Calcareous Sand in Acidic Environments

Calcareous sand contains massive shell fragments and is prone to liquefaction during seismic events. In this study, a series of cyclic simple shear tests were conducted to investigate the influences of acidic environments and multidirectional shearing on the pore pressure, shear strain, stiffness degradation, and liquefaction resistance responses of the unreinforced and fiber-reinforced calcareous sand. The test results show that the inclusion of fibers and longer exposure to acidic environments reduce the pore pressure and shear strain accumulation rate, whereas multidirectional shearing significantly accelerates the pore pressure buildup and exacerbates the shear strain development of calcareous sand. On this basis, a modified pore pressure empirical model for unreinforced and fiber-reinforced calcareous sand that can take into account acidic environments and multidirectional shearing conditions was established. Additionally, a unique trend was found between the stiffness degradation index and cycle ratio, indicating that the cycle ratio, ranging between 0.6 and 0.9, can be considered a critical stage for significant stiffness degradation in the tested calcareous sand. The resistance of calcareous sand to liquefaction is enhanced by fiber reinforcement and increasing acid erosion duration, whereas multidirectional shearing increases liquefaction susceptibility. Further, the presence of fibers exhibits satisfactory reinforcement efficiency even under multidirectional shearing conditions. The findings offer valuable insights into the characteristics of calcareous sand in acidic environments and highlight the potential of fiber reinforcement in mitigating the liquefaction risk.