Incipient flow velocity of non-uniform sediment particles by considering the additional mass force

Abstract

The sediments on the natural seabed are generally non-uniform particles. The incipient motion of non-uniform sediment particles has always been a key problem in the ocean engineering. In this paper, the incipient flow velocity of non-uniform sediment particles by considering the additional mass force is studied by means of mechanical analysis and comparative verification. Firstly, the mechanical model of non-uniform sediment particles is established in consideration of the seepage force, cohesion and the additional mass force caused by non-uniformity. Combined with the randomness of the position of non-uniform particles on the bed surface and the relative exposure degree of non-uniform particles, a systematic and comprehensive formula of the additional mass force is proposed. The mechanical equilibrium equations of critical incipient motion of the non-uniform sediment particles are established, and the critical incipient flow velocity of sediment particles under sliding instability and rolling instability are derived. Then, the accuracy and validity of the proposed formulas are verified by comparison with the results of flume test, field measurement and other formulas. Finally, the influence factors of the incipient flow velocity of non-uniform sediment particles are analyzed, and the change laws of influence factors are obtained. The results show that: 1) The incipient motion form of sediments on the natural seabed is generally the rolling instability. 2) The incipient flow velocity of sediment particles decreases first and then increases with particle diameter. 3) The incipient flow velocity of sediment particles increases with the dry bulk density. 4) The incipient flow velocity of sediment particles decreases with the increase of hydraulic gradient and relative exposure degree.