<p>Particle crushing alters the microstructure of geomaterials, impacting their physical and mechanical properties. Under high stress, large particles break into smaller, angular fragments, increasing packing density as fine particles fill voids, reducing porosity and void ratio. These changes significantly influence the pore structure, which governs fluid flow, permeability, and mechanical stability. Understanding pore-structure evolution is crucial for predicting geomaterial behavior in engineering applications such as oil and gas fields, foundation stability, and granular material performance. This study investigates the impact of particle crushing on the pore structure of granular soils and evaluates its effects on hydraulic properties, including relative permeability. It is well established that the water retention characteristics of soil reflect the microscopic pore-throat structure. Therefore, in this study, an optimization algorithm is employed to extract the pore structure of crushed soil samples from water retention curves available in the literature. The results reveal that the pore-size distribution becomes increasingly skewed as particle crushing progresses. However, pore connectivity improves with crushing. While saturated relative permeability decreases with particle crushing, relative permeability under unsaturated conditions exhibits an increasing trend. Geometrical tortuosity was also analyzed using the pore network, and the tortuosity evolution under progressive particle breakage demonstrates material-specific transport behavior: Angular Q-ROK sand exhibits a non-monotonic response due to competing mechanisms of pore blockage and throat reformation, while spherical glass beads display a monotonic decrease in tortuosity, attributed to enhanced packing efficiency and directional flow alignment. Furthermore, a comparison of pore-size evolution with an analytical fractal model indicates that particle crushing causes the pore-size distribution to deviate from a self-similar pattern.</p>