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Figure 3.8: Schematic of embankment after slip circle failure
Factors of safety of tailings dam embankments can be calculated from stability charts, limit
equilibrium methods, probabilistic analysis methods, finite element analysis methods, or a
combination thereof. The first three methods are discussed in this thesis.
3.2.1
ANCOLD recommendations
ANCOLD (2012) state that factors of safety depend on the consequences of failure, material
properties, and subsurface conditions: there are no ‘rules’ governing what constitutes an
acceptable factor of safety. Recommended minimum factors of safety for tailings dams under
different loading conditions are shown in Table 3.1.
Table 3.1: ANCOLD recommended factors of safety for tailings dams (ANCOLD, 2012).
Loading condition
Recommended minimum
factor of safety
Shear strength to be used
for evaluation
Long-term drained
1.5
Effective
Short-term undrained
(potential loss of containment)
1.5
Consolidated undrained
Short-term undrained
(no potential loss of containment)
1.3
Consolidated undrained
When there is ‘no potential loss of containment’ in short-term undrained conditions, a lower
factor of safety is recommended. This is not recommended for those cases analysed in this
thesis since the factor of safety assumes a ‘safer’ embankment with no loss of containment. It
cannot be determined that a tailings dam constructed to a factor of safety of 1.3 will never
have any loss of containment. Therefore, the minimum factor of safety, in this thesis, has been
calculated assuming the worst conditions (i.e. including the potential loss of containment) as
this is what better represents a real embankment failure.
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