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 Resources: Dredging and Offshore Engineering Lecture Notes

Home / Cutting of Sand, Clay and Rock / The Cutting of Sand /

    20-Lecture Notes Dredging Processes The Snow Plough Effect (1071)

The Snow Plough Effect When Cutting Water Saturated Sand

To predict the forces on excavating elements, two-dimensional cutting theories are used. Miedema 1987, 1989 and 1992 described the two-dimensional cutting theory for water saturated sand and its applications extensively. On a cutterhead, the blades are divided into small elements, at which a two dimensional cutting process is considered. However, this is correct only when the cutting edge of this element is perpendicular to the direction of the velocity of the element. For most elements this will not be the case. The cutting edge and the absolute velocity of the cutting edge will not be perpendicular. This means the elements can be considered to be inclined with respect to the direction of the cutting velocity. A component of the cutting velocity perpendicular to the cutting edge and a component parallel to the cutting edge can be distinguished. This second component results in a transverse force on the blade element, due to the friction between the soil and the blade. This force is also the cause of the transverse movement of the soil, the snow-plough effect. To predict the transverse force and the direction of motion of the soil on the blade, the equilibrium equations of force will have to be solved in three directions. Since there are four unknowns, three forces and the direction of the velocity of the soil on the blade, one additional equation is required. This equation follows from an equilibrium equation of velocity between the velocity of grains in the shear zone and the velocity of grains on the blade. Since the four equations are partly non-linear and implicit, they have to be solved iteratively. The results of solving these equations have been compared with the results of laboratory tests. The correlation between the two was very satisfactory, with respect to the magnitude of the forces and with respect to the direction of the forces and the flow of the soil on the blade.

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