Cyclic shear behavior of dredged soil under constant normal stress conditions

Dredged soil is widely adopted in coastal geotechnical engineering projects, yet its cyclic shear behavior has not been fully explored. In this study, we utilize the DJZ-500 shear apparatus to explore the influence of normal stress (125, 250, 375, 500 and 625 kPa), shear frequency (0.005, 0.01 and 0.04 Hz), and shear displacement amplitude (1, 3, 6 and 10 mm) on the cyclic shear behavior of coastal dredged soil. Our findings indicate that as normal stress increases, so does shear strength, while an increase in shear frequency does not correspondingly elevate shear strength. Furthermore, we observe that an optimal amplitude of shear displacement contributes to augmented shear strength, whereas larger or smaller amplitudes do not yield higher shear strengths. The shear strength is contingent upon a specific combination of shear cycle, normal stress and displacement amplitude. In addition, distinct from the shear strength variation law mainly determined by the normal stress level and the displacement amplitude, the damping ratio is solely affected by the shear displacement amplitude. We put forth an empirical formula considering normal stress, shear displacement amplitude, and shear frequency, which can forecast the cyclic shear behavior of dredged soil. This study provides substantial technical and theoretical aid for the design of coastal and offshore structures to withstand cyclical loads, such as those induced by waves and tidal forces.