It is seen that the most important initiating events may be attributed to overtopping and failure
of the foundation. Typically, overtopping is the result of scour of the foundation due to
extreme floods or malfunction of gates.
Studies have shown that the predominant reasons for dam failures are human errors as also
seen from Figure 1.20, which is based on data from Loss and Kennett (1987). From the figure
it is seen that various errors during the construction and the operation of the dams constitute
the predominant causes.
Unknown reason
18%Failure of foundation
36%Overtopping
33%Cracks in dams
7%Slides (banks or dam slopes)
5%Incorrect calculations
1%Figure 1.20: Illustration of the distribution of causes for dam failures (Loss and Kennett (1987)).
Failures of Offshore Structures
Failures of offshore installations are typically associated with either failure of the structural
system or parts thereof or failures and accidents in the process facilities causing loss of
production, damage and/or fatalities and injuries.
In Figure 1.21 and Figure 1.22 the distribution of initiating events causing failures of fixed
and mobile offshore facilities is shown for the period 1955-1990.
Other
Weather, flooding 11%
6%
Drifting grounding
8%Structural damage
32% Capsizing9%Collision
5%Fire / explosion
6%Blowout
23%Figure 1.21: Distribution of initiating events for failures of jack-up rigs (Bertrand and Escoffier (1987)).
Jack-up rigs are normally used for exploration purposes, moving from location to location,
drilling and test producing. This is also evident from the types of initiating events shown in
Figure 1.21 where it is seen that structural damages play an important role in the overall
picture and that the second-most important event is blow-out.