Development behavior of excess pore pressure in fiber-reinforced calcareous sand based on shear strain characteristics

Fiber reinforcement has been widely recognized as an effective approach for improving the liquefaction resistance of sandy soils. However, existing studies have predominantly focused on siliceous sand, whereas the liquefaction behavior of fiber-reinforced calcareous sand remains insufficiently understood. In this study, a series of cyclic simple shear tests was conducted to investigate the evolution of excess pore pressure and shear strain in fiber-reinforced calcareous sand, with emphasis on the effects of cyclic stress ratio (CSR) and fiber content ( F c ). The results indicate that increasing F c significantly improves the liquefaction resistance of calcareous sand, particularly under low CSR conditions. As CSR increases, the relationship between the excess pore pressure ratio ( r u ) and cycle ratio ( N / N L ) gradually evolves from an inverse S-shaped pattern to a hyperbolic pattern, whereas increasing F c produces the opposite trend. Clean calcareous sand exhibits a flow liquefaction mechanism, while fiber reinforcement promotes a cyclic mobility response similar to that observed in dense sand. Furthermore, the coupled evolution of r u and double-amplitude shear strain ( γ DA ) is closely correlated and is governed primarily by CSR rather than F c , exhibiting two distinct stages. Based on this relationship, a shear strain-based excess pore pressure generation model was developed for fiber-reinforced calcareous sand, providing a useful framework for effective stress-based seismic analysis of reinforced calcareous sand geotechnical structures.