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

The Delft Sand, Clay & Rock Cutting Model.
= 45° » = 39.7°
= 60° » = 36.8°
For the verification of the cutting tests an average value of 38 for the internal angle of friction is assumed. These
values are also more in accordance with the values of internal friction mentioned in Appendix K, where a value of
approximate 35 can be found with a pore percentage of 38.5%.
The same phenomena are observed in the determination of the angle of internal friction of the 105 m sand. The
assumption of a hydrostatic pressure behind the blade resulted also in too large values for the angle of internal
friction, analogously to the calculations of the 200 m sand. Here the following values are determined:
= 30° » = 46.2°
= 45° » = 38.7°
= 60° » = 40.3°
The determination of the angle of internal friction corrected for under pressure behind the blade W3 led to the
following values:
= 30° » = 38.7°
= 45° » = 34.0°
= 60° » = 38.4°
The low value of the angle of internal friction for the 45 blade can be explained by the fact that these tests are
performed for the first time in the new laboratory DE in a situation where the sand was not homogenous from top
to bottom. For the verification of the cutting forces and the water pressures is, for both sand types, chosen for a
soil/steel friction angle of 30 and an angle of internal friction of 38, as average values.
6.14. General Conclusions.
From the performed research the following general conclusions can be drawn:
1. Both the measured cutting forces as the measured water sub-pressures agree reasonably with the theory. For
both sand types is observed that the cutting forces and the water sub-pressures become smaller in comparison
with the theory, when the blade angle becomes larger. For the 30 blade the cutting forces and the water subpressures
are larger or equal to theoretical derived values, while for the 60 blade the theory can overestimate
the measurements with a factor 1.6. This can be explained by assuming that with an increasing blade angle
the cutting process becomes more discontinuous and therefore decreases the average volume strain rate. Slices
of sand shear off with dilatancy around the shear planes, while the dilatancy is less in the sand between the
shear planes. The theory can still be pretty useful since in dredging practice the used blade angles are between
30 and 45.
2. Side effects can considerably influence the direction of the cutting forces, although the magnitude of the
cutting forces is less disturbed. As a result of the side effects the cutting forces are aimed more downward.
3. Wear effects can also influence the direction of the cutting forces considerably, while also the magnitude of
the cutting forces is less disturbed. As a result of the wear the cutting forces are, however, aimed more
upwards.
6.15. The Snow Plough Effect.
To check the validity of the above derived theory, research has been carried out in the new laboratory DE. The
tests are carried out in hard packed water saturated sand, with a blade of 0.3 m by 0.2 m. The blade had a cutting
angle of 45 degrees and inclination angles of 0, 15, 30 and 45 degrees. The layer thicknesses were 2.5, 5 and 10
cm and the drag velocities 0.25, 0.5 and 1 m/s. Figure 6-57 and Figure 6-58 show the results with and without an
inclination angle of 45 degrees. The lines in this figure show the theoretical forces. As can be seen, the measured
forces match the theoretical forces well. Since the research is still in progress, further publications on this subject
will follow.
More results of measurements can be found in Appendix M and Appendix N
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