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

Clay Cutting.
Figure 7-22 shows the sum of the blade angle and the shear angle. When this sum is 90 degrees, the minimum of
the horizontal force is found. The graph shows clearly that this is the case for a 55 degree blade and an ac ratio
r=2.
See Appendix V: Clay Cutting Charts for more and higher resolution charts.
7.4.3. Specific Energy.
In the dredging industry, the specific cutting energy Esp is described as:
The amount of energy, that has to be added to a volume unit of soil (e.g. clay) to excavate the soil.
The dimension of the specific cutting energy is: kN/m² or kPa for sand and clay, while for rock often MN/m 2 or
MPa is used. For the case as described above, cutting with a straight blade with the direction of the cutting velocity
vc perpendicular to the blade (edge of the blade), the specific cutting energy Esp is:
E
sp
Fh
vc Fh
h w v h w
i c i
(7-58)
With the following equation for the horizontal cutting force Fh:
2 2
sin ( ) r sin ( )
F ch w ch w
sin( ) sin( ) sin( )
h s i s i HF
(7-59)
This gives for the specific cutting energy Esp:
E
c
c
2 2
Fh vc
sin ( ) r sin ( )
sp s s HF
hi w v
c sin( ) sin( ) sin( )
(7-60)
The cohesion c is half the UCS value, which can be related to the SPT value of the clay by a factor 12, so the
cohesion is related by a factor 6 to the SPT value (see Table 7-1), further, the strengthening λ factor will have a
value of about 2 at normal cutting velocities of meters per second, this gives:
s c 2 6SPT 12 SPT
(7-61)
Now a simplified equation for the specific energy Esp is found by:
2 2
sin ( ) r sin ( )
Esp
12 SPT 12 SPT
sin( ) sin( ) sin( )
HF
(7-62)
Figure 7-25 shows the specific energy Esp and the production Pc per 100 kW installed cutting power as a function
of the SPT value.
Table 7-1: Guide for Consistency of Fine-Grained Soil
(Lambe & Whitman (1979)).
SPT Penetration Estimated UCS (kPa)
(blows/ foot) Consistency
384
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