Environmental Engineering Reference
In-Depth Information
EL +575, top of new cutoff wall
New seepage blanket extension
EL +611.0, top parapet wall
EL +608, top of embankment
EL +567, pool of record
EL +500
Shell
EL +470
Alluvial
Alluvial
EL +435
Dolomite bedrock
New grout lines
Drawing not to scale
Figure 11.4
Earth dam remedial measures.
erosion and soil transport remained the dominant failure mode.
Figure 11.4
shows a sche-
matic of the proposed “permanent” remedial measures, which included a comprehensive
grouting program and construction of a concrete cutoff wall. Throughout the example, we
retained the English units used in all the project documents.
The engineering literature (e.g., Morgenstern, 1995) identifies three commonly accepted
ways of estimating event probabilities:
1. As result of frequent observations (historical data)
2. Derived from probability theory (mathematical modeling)
3. Quantification of expert
For the dam in the example, we used quantification of expert judgment (subjective prob-
abilities) to estimate failure probabilities from internal erosion for a wide range of pool
elevations. The set of probability estimates obtained are summarized in
Table 11.2
and
portrayed in
Figure 11.5.
These estimated internal erosion failure probabilities are conditioned on the occurrence
of the peak pool elevation. In
Table 11.2
,
the probability of failure numbers in bold font
were obtained by estimation and the numbers in regular font obtained by interpolation.
A further refinement of the failure probability estimates would consider maintaining a
given pool elevation for a determined time period during which a particular step in the
failure mode sequence would have the opportunity to develop, instead of simply using
peak values.
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