Understanding the sedimentation behavior of dredged slurry under shear is essential for managing disposal ponds and land reclamation. This study developed a rotating shear settling device to systematically investigate the structural evolution and sedimentation response of dredged slurry (Tianjin mud) under varying shear intensities (0–4.89 s -1 ) and initial water contents (157%–377%). Results revealed that, across tests with increasing applied shear intensities, the slurry exhibited four distinct modes: structural reconstruction, surface particle detachment, critical instability, and complete disintegration. During the critical instability mode, surface erosion accelerated dramatically, releasing a large number of fine particles (0.002–0.005 mm) and causing transient or complete disappearance of the sedimentation interface. The critical rotational speed decreased with increasing initial water content (from ~40 rpm at 5× liquid limit to ~20 rpm at 9–12× liquid limit). Particles of 0.002–0.005 mm were most susceptible to shear-induced detachment, while the concentration of sub‑0.002 mm particles served as an indicator of aggregate fragmentation. Based on these findings, we propose that the critical shear threshold represents the macroscopic structural strength of the floc network. Two complementary engineering strategies are derived: keeping shear below the critical threshold to maintain a clear supernatant and minimize fine-particle overflow (environmental control), or exceeding it to reduce vertical grain-size segregation at the cost of increased turbidity (fill-uniformity regulation).