Understanding the world of sand and water
This book contains chapter 4.2 from the main book "Dredging Technology Book 1". One of the most striking phenomena when a suction tube makes a deep suction pit in a sand bottom is the appearance of a steep slowly horizontal moving benches that produce loose sand flowing in a density current towards the suction mouth. This process is called “Breaching”. This density current flows over hundreds of meters distance along very flat (5-20°) slopes towards the suction mouth.
Using these two phenomena it is possible to produce enormous amounts of sand from a single stationary position.
The reason behind the steep breaches is the phenomenon called: “Dilatancy”. The reason of the very long and flat slopes under the density currents is the phenomenon called “Hindered settling”. Erosion is also the basis of the sand production process under a drag head using high speed waterjets with jet water velocities up to 30 m/s and more. This type of erosion is called “High speed erosion of sand”.