Environmental Engineering Reference
In-Depth Information
Table 8.1.
Statistics of failures of large embankment dams up to 1986 (Foster et al., 1998, 2000a).
% Total failures
(1)
% Failures pre
% Failures post
1950
(2)
1950
(3)
Mode of failure
Overtopping
34.2
36.2
32.2
Spillway/gate (appurtenant works)
12.8
17.2
8.5
Piping through embankment
32.5
29.3
35.5
Piping from embankment into foundation
1.7
0
3.4
Piping through foundation
15.4
15.5
15.3
Downstream slide
3.4
6.9
0
Upstream slide
0.9
0
1.7
Earthquake
1.7
0
3.4
Totals
(3)
102.6
105.1
100
Total overtopping and
48.4
53.4
40.7
appurtenant works
Total piping
46.9
43.1
54.2
Total slides
5.5
6.9
1.6
Total no. of embankment dam failures
124
61
63
(1)
Percentages based on the % of cases where the mode of failure is known.
(2)
Percentages are for failures of embankment dams in operation only, i.e. excluding failures during
construction.
(3)
Percentages do not necessarily sum to 100% as some dams were classified as multiple modes of failure.
Table 8.2.
Statistics of failures and accidents by internal erosion and piping of embankment
dams up to 1986 (Adapted from Foster et al., 1998).
10
3
)
Average probability during life of dam (
Piping in embankment
Piping in foundation
Zoning category
Failures
Accidents
Failures
Accidents
Homogeneous earthfill
16.0
9.2
3.0
11.2
Earthfill with horizontal filter
1.5
0.6
-
3.9
Earthfill with rock toe
8.9
8.0
7.0
3.9
Zoned earthfill
1.2
2.4
0.4
4.6
Zoned earth and rockfill
1.2
7.3
-
7.6
Central core earth and rockfill
1.1
22.0
-
9.8
Concrete face earthfill
5.3
2.4
10.4
5.8
Concrete face rockfill
1
3.5
-
-
Puddle core earthfill
9.3
20.7
-
-
Concrete core wall earthfill
1
8.1
11.8
4.9
Concrete core wall rockfill
1
21.6
-
-
Hydraulic fill
1
32.4
15.7
91.8
Zoning unknown
-
-
-
-
All embankment types
3.5
26.8
1.7
6.2
dam, that modern criteria for acceptable factors of safety are reasonably conservative, and
that most dams will show excessive deformation if they are marginally stable, allowing
remedial works or lowering of the reservoir water level before failure occurs.
ures and accidents.
In Table 8.4, the annual probabilities have been calculated allowing for the estimated
average life of the dams up to 1986.