Force measurements on an inclined plate moving a sediment/sand bed

Abstract

To provide data for the numerical modelling effort on the impact of seabed nodule harvesting on the marine environment and infrastructure, an experimental study of the interaction between a simple lab-scale nodule harvester and sediment/sand is carried out. The lab-scale harvester is simplified by a moving inclined plate and the seabed sediment is modelled by a tank containing water and bentonite suspension, or sand, as sediment substitute. The forces acting on the plate by the sediment are measured and the dispersion of sediment particles in the water tank is visualized. Experiment results show that, for a high enough mass fraction, the bentonite suspension displays a yield-stress behavior; and indeed, a gel-like structure suspension may result. Sand, being non-cohesive in nature, gives a much greater acting force on the plate than bentonite sediment. Gel-like structure clay suspension gives a much greater force than fluidified suspension. Once dispersed into water, sand particles quickly settle while clay particles take a longer time to settle and form an emulsion layer on top of the sediment. The experiment results serve both as a means to calibrate and validate the numerical modelling, as well as to gain physical insights into the seabed/structure interaction.