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

The Delft Sand, Clay & Rock Cutting Model.
2
2
m m 4 1
min UCS
2
2 1
m m 4 1
max UCS
2
2 1
2
2
(8-10)
This gives for the center of the Mohr circle:
UCS m m 4 1
center 1
2
2
2 1
2
2
UCS m m 4 1
max 1
2
2
2 1
2
2
(8-11)
Figure 8-8: Brittle, semi brittle and ductile failure.
Figure 8-17 shows the Mogi criterion both for the top of the Mohr circle curve and the failure curve. Left of the
Mogi criterion point there will be brittle failure, on the right there will be pseudo-ductile failure. When the
coefficient α increases, the Mogi points move to the left.
In the case of a straight failure plane this gives for the normal and shear stress:
c 1
sin
cos
1
and c tan
tan
1
1 sin
cos
1
(8-12)
Which is also shown in Figure 8-17. If the angle of internal friction is to high, the brittle-ductile transition will
never be reached. The criterion for this is:
1 sin
1
(8-13)
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