The Delft Sand, Clay & Rock Cutting Model, 2019a

Clay Cutting.
Chapter 7: Clay Cutting.
7.1. Definitions.
Figure 7-1: The cutting process, definitions.
Definitions:
1. A: The blade tip.
2. B: End of the shear plane.
3. C: The blade top.
4. A-B: The shear plane.
5. A-C: The blade surface.
6. hb: The height of the blade.
7. hi: The thickness of the layer cut.
8. vc: The cutting velocity.
9. α: The blade angle.
10. β: The shear angle.
11. Fh: The horizontal force, the arrow gives the positive direction.
12. Fv: The vertical force, the arrow gives the positive direction.
7.2. Introduction.
Hatamura and Chijiiwa (1975), (1976A), (1976B), (1977A) and (1977B) distinguished three failure mechanisms
in soil cutting. The Shear Type, the Flow Type and the Tear Type. The Flow Type and the Tear Type occur in
materials without an angle of internal friction. The Shear Type occurs in materials with an angle of internal friction
like sand. A fourth failure mechanism can be distinguished (Miedema (1992)), the Curling Type, as is known in
metal cutting. Although it seems that the curling of the chip cut is part of the flow of the material, whether the
Curling Type or the Flow Type occurs depends on several conditions. The Curling Type in general will occur if
the adhesive force on the blade is large with respect to the normal force on the shear plane. Whether the Curling
Type results in pure curling or buckling of the layer cut giving obstruction of the flow depends on different
parameters.
Figure 7-2 illustrates the Curling Type mechanism, Figure 7-3 the Flow Type mechanism and Figure 7-4 the
Tear Type mechanism as they occur when cutting clay or loam. To predict which type of failure mechanism will
occur under given conditions with specific soil, a formulation for the cutting forces has to be derived. The
derivation is made under the assumption that the stresses on the shear plane and the blade are constant and equal
to the average stresses acting on the surfaces. Figure 7-1 gives some definitions regarding the cutting process. The
line A-B is considered to be the shear plane, while the line A-C is the contact area between the blade and the soil.
The blade angle is named α and the shear angle β. The blade is moving from left to right with a cutting velocity
vc. The thickness of the layer cut is hi and the vertical height of the blade hb. The horizontal force on the blade Fh
is positive from right to left always opposite to the direction of the cutting velocity vc. The vertical force on the
blade Fv is positive downwards.
Copyright © Dr.ir. S.A. Miedema TOC Page 191 of 454