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

The Delft Sand, Clay & Rock Cutting Model.
Figure 9-4: The definitions of
the cutting process.
Figure 9-5: The Flow Type
cutting mechanism.
Figure 9-6: The Crushed Type cutting mechanism.
Figure 9-7 illustrates the forces on the layer of rock cut. The forces acting on this layer are:
1. A normal force acting on the shear surface N1 resulting from the grain stresses.
2. A shear force S1 as a result of internal friction N1·tan(.
3. A force W1 as a result of water under pressure in the shear zone.
4. A shear force C as a result of the cohesive shear strength c or c. This force can be calculated by multiplying
the cohesive shear strength c/c with the area of the shear plane.
5. A force normal to the blade N2 resulting from the grain stresses.
6. A shear force S2 as a result of the external friction N2·tan(.
7. A shear force A as a result of pure adhesion between the rock and the blade a or a. This force can be calculated
by multiplying the adhesive shear strength a/a of the rock with the contact area between the rock and the
blade. In most rocks this force will be absent.
8. A force W2 as a result of water under pressure on the blade
The normal force N1 and the shear force S1 on the shear plane can be combined to a resulting grain force K1.
2 2
1 1 1
K N S
(9-2)
The forces acting on a straight blade when cutting rock, can be distinguished as:
1. A force normal to the blade N2 resulting from the grain stresses.
2. A shear force S2 as a result of the external friction N2·tan(.
3. A shear force A as a result of pure adhesion between the rock and the blade a or c. This force can be calculated
by multiplying the adhesive shear strength a/a of the rock with the contact area between the rock and the
blade. In most rocks this force will be absent.
4. A force W2 as a result of water under pressure on the blade
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