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2.2.3
Foundation failure
The foundation properties are important in the design and construction of a tailings dam
embankment. Potential planes of weaknesses are inherent at the interface between the
foundation and embankment. Sliding and bearing failure are possible failure types as well as
compound or translational failures arising from the slope itself.
Foundation failure can occur during staged construction as the existing embankments are
treated as foundations for subsequent dyke placement and compaction As the dam wall height
increases, the added weight of the structure increases the pore water pressures in the existing
dyke. The excess pore water pressures dissipate over time, which in turn increases the
effective stresses and the strength of the foundation, improving the factor of safety (Duncan
and Wright, 2005). The strength of the existing foundation is important as it may be sufficient
for a particular dam height, but even with the increased strength caused by the increase in
self-weight; the foundation may be insufficient to maintain overall stability as the height is
increased (ICOLD Bulletin 106). Embankment construction should be timed so that the
material has had sufficient time for consolidation before a new dyke is constructed.
2.2.4
Overtopping
Overtopping can occur when there is a rise in water levels, due to high rainfall, flood waters,
or mismanagement of tailings entering the pond. If overtopping occurs, the embankment wall
will be breached and possible erosion of the downward slope can lead to complete failure of
the dam (Lottermoser, 2007). Effective diversion of surface water and run off is a key
component in the design of tailings dams to prevent excess storm water entering the pond (US
EPA, 1994).
Figure 2.12: Example of an embankment overtopping in Googong, New South Wales 1976 (EHA, 2008)
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