Direct shear behavior of dredged soil under dynamic normal load conditions

Dredged soil is commonly encountered in estuarine and coastal engineering constructions; however, its dynamic frictional behavior is still unclear. In this research, DJZ-500 shear apparatus was utilized for conducting direct shear test on the dredged soil. The periodic normal stress was employed in the vertical direction of soil sample, and simultaneously, shear stress was applied in the horizontal direction to supply a constant speed. The influences of different shear rates, dynamic normal stress frequencies, and dynamic normal stress amplitudes on the shear properties of the dredged soil under dynamic normal stress conditions were explored. It was found that shear stress periodically varied with the periodic normal stress, characterizing a phase lag with the peak shear stress. The dynamic normal stress manifested an enhancement effect and also a weakening effect on the shear strength. Generally, a small dynamic normal stress frequency, a high shear speed, and an appropriate dynamic normal stress amplitude induced frictional strengthening, whereas a small shear speed, a large dynamic normal stress frequency, and a very large or small dynamic normal stress amplitude caused frictional weakening. Therefore, the dynamic frictional behavior of the dredged soil depended on shear velocity and the frequency and amplitude of dynamic normal stress. The results of this paper provide technical support to improve the resistance of coastal constructions to dynamic disturbances, such as earth tides, ocean waves, earthquakes, typhoons, and traffic loads.