15.2 Engineering Stability Analyses of the Dams
225
Table 15.3 Geotechnical parameters of the soils in cross sections of Dam 3
Zone
Name
γ (kN m −3 )
C (kPa)
ϕ (°)
1
Compacted till
21
0
35
2
Tailings
19.5
0
30–(5.7) (liqu.)
3
Crushed waste
20
0
38
4
Silty clay
16.5
0
28
Geotechnical conditions for Dam 4 are scarce and have been summarized in
Sect. 11.1.2.
15.2 Engineering Stability Analyses of the Dams
The engineers have defined the following FoS for the various dams under various
analysis conditions:
• USA undrained stress;
• ESA effective stress;
• pseudostatic;
as shown in Table 15.4.
Let’s comment on the values of the FoS of the dams in this portfolio.
An exception being made of Dam 4, which is clearly a “bad apple”, the FoS have
very similar values in USA for Dams 2 and 3, in ESA for Dams 1A, 1B and 2. Finally,
there are very similar FoS under pseudo-static conditions for Dams 1, 2 and 3. We
will see later that the image we obtain with the probability of failure is much more
defined, with more evident variations from one dam to the next. This extra definition
is very important when a risk prioritization of a large portfolio is sought.
Table 15.4 Results of the engineers’ stability analyses for the various dams of the portfolio
Dam
USA
ESA
Pseudo-static
1A
n/a
1.61–1.68
1.18–1.23 for 1/475 Operating base
earthquake (OBE) and 1/1500 MCE
1B
n/a
1.59–1.65
1.15.1.26
for 1/475 (OBE)
2
Rapid drawdown
1.63–1.76
1.59–1.68
1.28–1.33 for 1/1000
3
1.6
1.29–1.35
1.2 for 1/2475 maximum credible
earthquake (MCE)
4
Refer to Tables 11.1 and 11.2 in
Sect. 11.1.2:
FoS = 1 to 1.35, average 1.17
225
Table 15.3 Geotechnical parameters of the soils in cross sections of Dam 3
Zone
Name
γ (kN m −3 )
C (kPa)
ϕ (°)
1
Compacted till
21
0
35
2
Tailings
19.5
0
30–(5.7) (liqu.)
3
Crushed waste
20
0
38
4
Silty clay
16.5
0
28
Geotechnical conditions for Dam 4 are scarce and have been summarized in
Sect. 11.1.2.
15.2 Engineering Stability Analyses of the Dams
The engineers have defined the following FoS for the various dams under various
analysis conditions:
• USA undrained stress;
• ESA effective stress;
• pseudostatic;
as shown in Table 15.4.
Let’s comment on the values of the FoS of the dams in this portfolio.
An exception being made of Dam 4, which is clearly a “bad apple”, the FoS have
very similar values in USA for Dams 2 and 3, in ESA for Dams 1A, 1B and 2. Finally,
there are very similar FoS under pseudo-static conditions for Dams 1, 2 and 3. We
will see later that the image we obtain with the probability of failure is much more
defined, with more evident variations from one dam to the next. This extra definition
is very important when a risk prioritization of a large portfolio is sought.
Table 15.4 Results of the engineers’ stability analyses for the various dams of the portfolio
Dam
USA
ESA
Pseudo-static
1A
n/a
1.61–1.68
1.18–1.23 for 1/475 Operating base
earthquake (OBE) and 1/1500 MCE
1B
n/a
1.59–1.65
1.15.1.26
for 1/475 (OBE)
2
Rapid drawdown
1.63–1.76
1.59–1.68
1.28–1.33 for 1/1000
3
1.6
1.29–1.35
1.2 for 1/2475 maximum credible
earthquake (MCE)
4
Refer to Tables 11.1 and 11.2 in
Sect. 11.1.2:
FoS = 1 to 1.35, average 1.17