Environmental Engineering Reference
In-Depth Information
11.2.2 example of risk assessment for an earth dam
based on the empirical FS versus p(f) charts
This section presents a simplified risk analysis to evaluate the safety of an earth dam with
respect to failure by internal erosion and soil transport. In addition, the risk analysis
addresses the effect on risk or level of safety of proposed remedial measures for the dam.
The risk assessment summarized below covers only part of the complete risk picture for
the dam. Other potential failure modes exist, but failure by internal erosion/piping was
considered the dominant failure mode for structure. The assessment involved the follow-
ing steps:
• Estimation of failure probabilities versus peak pool elevation
• Estimation of pool elevation annual exceedance probabilities (AEPs)
• Estimation of potential loss of life versus pool elevation at time of failure
• Comparison of results with risk evaluation guidelines
11.2.2.1 Estimation of failure probabilities versus peak pool
elevation: Example from engineering practice
The earth dam, an actual project from our engineering practice, is founded on karst and
developed a sinkhole in the upstream slope during a high reservoir level event as shown
schematically in
Figure 11.3
.
The sinkhole was temporarily repaired but failure by internal
Sinkhole
EL +611.0, top parapet wall
EL +608, top of embankment
EL +567, pool of record
River
channel
exit face
Shell
EL +500
Shell
Dental
concrete
EL +470
Alluvial
Alluvial
EL +435
“Pipe”
Bedrock
Bedrock
Transported
“shell”
material
Grout
curtain
Drawing not to scale
Figure 11.3
Internal erosion/soil transport potential failure mode.
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