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

A Wedge in Clay Cutting.
Chapter 13:
A Wedge in Clay Cutting.
13.1. Introduction.
Clay cutting is dominated by cohesive and adhesive forces. Pore pressure forces, gravitational forces and inertial
forces do not play a role or can be neglected. Clay cutting is regarded to be an undrained process resulting in the
φ=0 concept, meaning that the internal and external friction angles can be considered to be zero. Because of the
absence of internal and external friction angles, the sine of the sum of the 4 angles in the denominator of the
equation for the cutting forces will less likely approach or exceed 180 degrees, resulting in very large or even
negative forces. In clay only the blade angle and the shear angle play a role. Now the shear angle will in general
be larger in the clay cutting process compared with the sand cutting process, still very large blade angles are
required in order to approach the 180 degrees. The shear angle may have values of 30-50 degrees for a blade angle
of 90 degrees, still not approaching the total of 180 degrees enough. Blade angles of around 150 degrees will be
required to have a sum approaching 180 degrees. In normal dredging the blade angles will be up to about 60
degrees, but the front of a drag head of a trailing suction hopper dredge has an angle larger than 90 degrees, also
in the problem of ice berg scour large angles may occur and usually tunnel boring machines have blades with large
blade angles. So the problem of having large blade angles is relevant and the transition from the no-wedge
mechanism to the wedge mechanism is of interest in engineering practice. Figure 13-1 shows the definitions of the
wedge mechanism.
Figure 13-1: The occurrence of a wedge in clay cutting.
Definitions:
1. A: The wedge tip.
2. B: End of the shear plane.
3. C: The blade top.
4. D: The blade tip.
5. A-B: The shear plane.
6. A-C: The wedge surface.
7. A-D: The wedge bottom.
8. D-C: The blade surface.
9. hb: The height of the blade.
10. hi: The thickness of the layer cut.
11. vc: The cutting velocity.
12. α: The blade angle.
13. β: The shear angle.
14. Fh: The horizontal force, the arrow gives the positive direction.
15. Fv: The vertical force, the arrow gives the positive direction.
Copyright © Dr.ir. S.A. Miedema TOC Page 377 of 454