220
15 Risk-Informed Decision Making
– It includes consequences, when applicable, analyses from extant reports and
from recent research (Chap. 12).
• It is useful to remember that historically the probability of dam failure ranges
from 10
−3 to 2 * 10
−4 for “generic” tailings dams (see Table 4.1, Sect. 4.1), with
respect to a range from 10
−5 to 3 * 10
−6 for top of class water dams, which can be
considered at “credibility threshold”. These ranges can be used to benchmark the
result of this assessment to historic “world-wide portfolio” performances (Chap. 4).
As noted earlier, these historical data have to be taken with prudence, due to the
inconsistent way of attributing the principal cause of failure and, for example, the
large number of “unknown”, “not available” and “other” categories.
We will use a portfolio of four dams, namely Dam 1, 2, 3, 4, with one major
external interdependency. One of the four dams will be studied at two distinct raise
levels (Dam 1A, Dam 1B).
These dams are all real-life dams belonging to different clients around the world.
In order to maintain confidentiality, we have altered the dams profiles and the geotechnical parameters of the materials, and we have performed several data alterations.
Due to obvious limitations of space we will develop each case only to the level
required for the discussion and the points we want to make.
15.1 Portfolio Description
This section describes the system constituted by the dams and their internal and
external interdependencies. In all the dams the engineers declared the bedrock to be
competent and free of weak layers and unfavorable discontinuities. Further, liquefaction (see Sect. 9.3) was disregarded by the engineers as a potential failure factor.
15.1.1 General Descriptions of the Dams
Dam 1A is an intermediate situation of Dam 1, i.e., the raise of Dam 1 at 100 m
altitude (Fig. 15.1).
Piezometers show phreatic levels at bedrock in zones 1 and 2 downstream of
zone 3.
Inclinometers have not shown any significant discontinuity, i.e., there is no
suspicion of instability. Geotechnical parameters of the various soils are defined
in Table 15.1.
Dam 1B (Fig. 15.2) is the same dam as Fig. 15.1, but at its final altitude of 162 m.
No changes of conditions with respect to Fig. 15.1.
Dam 2 is a water retention dam (Fig. 15.3) which displays an inter-dependency
with Dam 3.
15 Risk-Informed Decision Making
– It includes consequences, when applicable, analyses from extant reports and
from recent research (Chap. 12).
• It is useful to remember that historically the probability of dam failure ranges
from 10
−3 to 2 * 10
−4 for “generic” tailings dams (see Table 4.1, Sect. 4.1), with
respect to a range from 10
−5 to 3 * 10
−6 for top of class water dams, which can be
considered at “credibility threshold”. These ranges can be used to benchmark the
result of this assessment to historic “world-wide portfolio” performances (Chap. 4).
As noted earlier, these historical data have to be taken with prudence, due to the
inconsistent way of attributing the principal cause of failure and, for example, the
large number of “unknown”, “not available” and “other” categories.
We will use a portfolio of four dams, namely Dam 1, 2, 3, 4, with one major
external interdependency. One of the four dams will be studied at two distinct raise
levels (Dam 1A, Dam 1B).
These dams are all real-life dams belonging to different clients around the world.
In order to maintain confidentiality, we have altered the dams profiles and the geotechnical parameters of the materials, and we have performed several data alterations.
Due to obvious limitations of space we will develop each case only to the level
required for the discussion and the points we want to make.
15.1 Portfolio Description
This section describes the system constituted by the dams and their internal and
external interdependencies. In all the dams the engineers declared the bedrock to be
competent and free of weak layers and unfavorable discontinuities. Further, liquefaction (see Sect. 9.3) was disregarded by the engineers as a potential failure factor.
15.1.1 General Descriptions of the Dams
Dam 1A is an intermediate situation of Dam 1, i.e., the raise of Dam 1 at 100 m
altitude (Fig. 15.1).
Piezometers show phreatic levels at bedrock in zones 1 and 2 downstream of
zone 3.
Inclinometers have not shown any significant discontinuity, i.e., there is no
suspicion of instability. Geotechnical parameters of the various soils are defined
in Table 15.1.
Dam 1B (Fig. 15.2) is the same dam as Fig. 15.1, but at its final altitude of 162 m.
No changes of conditions with respect to Fig. 15.1.
Dam 2 is a water retention dam (Fig. 15.3) which displays an inter-dependency
with Dam 3.