Finally in Figure 1.18 it is illustrated whether and how the failures and errors might have been
avoided. From this figure it is evident that control is one of the most important risk treatment
measures, a fact, which is generally realized by most engineers, but unfortunately not fully
appreciated. Often, control is considered an obstruction of the routines of the daily work.
However, normal care or precaution also plays an important role. It is seen that a smaller part
of the failures and errors is actually unavoidable. Thus, the potential for improvements is
large.
Normal care
32%Additional
control
55%Unavoidable
13%Figure 1.18: Illustration of the relative distribution of risk treatment measures which might have
circumvented the failures and errors (Matousek and Schneider (1976)).
Failure of Dam Structures
The failure mode, which has the most severe consequences for dam structures, is wall rupture,
as this type of failure will release a flood wave potentially resulting in severe damages and a
large number of fatalities and/or injuries downstream of the dam structure. Typically, failures
of dams are the result of extreme load conditions exceeding the resistance of the dam
structures. Extreme load conditions may be caused by large floods, earthquakes and failures
of upstream dams. The resistance of the dam structure depends on the characteristics of the
dam structure materials and the soil and rock properties. Such properties exhibit a certain
inherent variability and may be influenced by external factors such as degradation processes
and e.g. pore pressures.
Initiating events for dam failures have been analyzed by Blind (1983) and some results are
illustrated in Figure 1.19.
Unknown reason
18%Failure of foundation
36%Overtopping
33%Cracks in dams
7%Slides (banks or dam slopes)
5%Incorrect calculations
1%Figure 1.19: Distribution of initiating events for dam structures (Blind (1983)).