Practical risk assessment for embankments, dams, and slopes - Risk and Reliability in Geotechnical Engineering - page 437

620
610
600
590
580
570
560
550
540
530

370

366

35 362

355

351

347

33 343

331

31 323

30 308

260

220

180

140

100

81 91

520
510
500
490
480
470
460

Pontential life loss versus pool elevation

72

62

2 27 35

11

1

0 100 200 300 400

Pontential life loss

Figure 11.6 Potential life loss versus pool elevation at failure for earth dam.

Based on these estimates, we used linear interpolation to obtain the values for all the pool
elevations shown in Figure 11.6 . Experience at other dams suggest that a more detailed sim-
ulation with input on evacuation effectiveness from the Emergency Management Agencies
could lead to reduced potential loss of life estimates.

11.2.2.4 Comparison of results with risk evaluation guidelines
Figure 11.7 summarizes the U.S. Bureau of Reclamation Public Protection Guidelines for
dams in a plot that shows ALL in lives/year on the sloping lines and total APF on the vertical
axis. Figure 11.7 is generally known as an f-N plot and portrays “a discrete, noncumula-
tive probability distribution in which each probability-consequence (f, N) pair is plotted”
(Bowles, 2007). As mentioned earlier, in this particular case, the APF refers to failure from
internal erosion/soil transport. We obtained the ALL and APF estimates shown in Table
11.4 by calculating the sums shown in Equations 11.3 and 11.4 over each of the peak pool
elevation intervals shown in Table 11.2 :

ALL =∑ ∗ f N

ii

(11.3)

i

APF = ∑ i f i (11.4)

where
f i is the estimated annual probability of failure for the ith peak pool elevation interval = Pi i × p i
P i is the estimated (incremental) probability of occurrence of the ith peak pool elevation
during a year for the center of the elevation interval