The variation of the rheological properties of coastal mud after being subjected to prior shear loadings

Muddy seabeds in estuarine and coastal regions play a critical role in dissipating wave energy, thereby reducing wave heights and mitigating coastal hazards. Accurate prediction of wave–mud interactions strongly depends on the determination of the rheological properties of coastal mud. However, the influence of prior shear loadings—particularly oscillatory loading induced by waves—on the rheological behavior of mud has not yet been comprehensively examined. To investigate the dynamic evolution of rheological properties of coastal mud under different prior shear conditions, a series of rheological experiments was performed on the samples collected from the tidal flats of Zhoushan Archipelago. The effects of the magnitude and frequency of the prior shear loadings on the rheological properties of the mud sample were systematically analyzed. The results revealed that prior shear loadings significantly affect the rheological properties of the mud sample in the solid state before the first yielding, whereas their influence on the solid-fluidic transitional and fluidic state after first yielding is relatively minor. Furthermore, the magnitude of prior shear loadings exerts a strong influence on the static yield stress of the mud sample, while its effect on the fluidic yield stress is comparatively weak. In addition, when the magnitude of prior shear loadings is lower than the fluidic yield stress, the rheological properties exhibit a significant decrease with increasing load frequency only when the frequency is high enough; in contrast, when the load magnitude exceeds the fluidic yield stress, these properties continuously decrease with increasing frequency. Moreover, a critical densification load is identified, which separates structural loosening from shear-induced densification. Overall, this study provides novel insights into the rheological properties of coastal mud, offering valuable scientific support for improving predictions of wave–mud interactions and understanding processes such as fluid mud formation and sediment transport in coastal environments.