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

Saturated Sand Cutting.
The equations derived (6-112) and (6-116) are used to determine the values of and from the cutting tests carried
out. The soil/steel friction angle can quite easily be determined, with the remark that the side and wear effects can
influence the results from this equation slightly. The soil/steel friction angle, determined with this method, is
therefore a gross value. This value, however, is of great practical importance, because the side and wear effects
that occur in practice are included in this value.
The soil/steel friction angle δ, determined with this method, varied between 24 and 35, with an average of
approximately 30. For both types of sand almost the same results were found for the soil/steel friction angle. A
clear tendency towards stress or blade angle dependency of the soil/steel angle of friction is not observed. This in
contrast to Van Leussen and Nieuwenhuis (1984), who found a blade angle dependency according Hettiaratchi
and Reece (1974).
Figure 6-53: The location of the pressure transducer behind the blade.
Harder to determine is the angle of internal friction. The following average values for the angle of internal friction
are found, for the 200 m sand:
= 30° » = 46.7°
= 45° » = 45.9°
= 60° » = 41.0°
These values are high above the angle of internal friction that is determined with soil mechanical research
according to Appendix K, for a pore percentage of 38.5%. From equation (6-116) it can be derived that the presence
of sub-pressure behind the blade makes the angle of internal friction smaller and also that this reduction is larger
when the blade angle is smaller. Within the test program space is created to perform experiments where the subpressure
is measured both on and behind the blade (Figure 6-53). Pressure transducer p 1 is removed from the blade
and mounted behind the blade tip. Although the number of measurements was too limited to base a theoretical or
empirical model on, these measurements have slightly increased the understanding of the sub-pressure behind the
blade. Behind the blade tip sub-pressures are measured, with a value of 30% to 60% of the peak pressure on the
blade. The highest sub-pressure behind the blade was measured with the 30 blade. This can be explained by the
wedge shaped space behind the blade. The following empirical equation gives an estimate of the force W3 based
on these measurements:
W
0.3 cot( ) W
(6-117)
3 2
The determination of the angle of internal friction corrected for under pressure behind the blade W3 led to the
following values:
= 30° » = 36.6°
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