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surface was tangential to the foundation, there was an assumed plane of weakness between the
two layers. Azami, Yacoub & Curran (2012) state that “The stability of slopes is highly
dependent on the presence and configuration of the weak planes in the materials and the shape
and possible slip surface is also influenced by the orientation of the weak planes.”. The
material in the foundation is often different from that in the embankment material, especially
for tailings dams since the embankments are constructed from coarse mine tailings. As
discussed in Section 2.2.7, liners can be used between the foundation and embankments
which can also act as a plane of weakness.
5.4.3
Drained analysis
Table 5.12: Case 3 factors of safety from spreadsheets and SLOPE/W for drained conditions
Method
Bishop
simplified
Fellenius
Janbu
simplified
Morgenstern
and Price
Spencer
General
limit
equilibrium
Spreadsheet
1.479
1.449
n/a
n/a
n/a
n/a
SLOPE/W
1.479
1.448
1.447
1.479
1.479
1.479
Spreadsheet
1.477
1.448
n/a
n/a
n/a
n/a
SLOPE/W
1.478
1.445
1.445
1.477
1.477
1.477
No. of
slices
5
20
1.477
Elevation (m)
15
10
5
0
0
5
10
15
20
25
30
35
40
Distance (m)
Figure 5.11: Most critical slip circle in drained SLOPE/W analysis with 20 slices
The drained analysis for Case 3 was unaffected by the stiff foundation. In comparison to Case
1, the embankment failed the same way in which it would have if there was no foundation.
This was because the soil had a high angle of shearing resistance (35°) in the long-term and
was sufficiently strong that the strength of the embankment had no effect.
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