46
4 Historic Failures “Statistics”
Fig. 4.7 In case (C) the base case is mitigated with M2 = inspections during service life
Fig. 4.8 In case (D) the base case is mitigated with M1 = peer review AND M2 = inspections
By adopting a very simplified approach to CCF it is possible to assume that
insufficient rigour, complacency, conflict of interest, common excessive audacious
approach in M1 and M2 could reduce the expected positive result of any mitigation
to nil.
Four levels of mitigation (Fig. 4.3, i.e., the base case, Fig. 4.6, 4.7, 4.8) were
studied:
(A) Base case with no M1 or M2, depicted in Sect. 4.2.3, Fig. 4.3.
(B) Base case with M1 (Fig. 4.6), i.e., independent peer review (including sensible
RBDM procedures and risk assessment from project inception).
(C) Base case with M2 (Fig. 4.7), i.e., Inspections paired with sensible RBDM
procedures and risk assessment from project inception.
(D) Base case with M1, M2 (Fig. 4.8) (descriptions as above) implemented.
By using ICOLD 1994 and World-wide 1910–2009 data (Tables 4.2 and 4.3) and
the various mitigation variants of the model described above it is possible to evaluate
the probability of failure of a dam under the considered hazard selection for a selected
average life span of 30 years. In order to perform the calculations, one further step is
necessary, as the probability of each hazard hitting a function has to be determined.
The first framing is easy in a professional environment: all those probabilities
lie in the range 10
−2 –10
−4 . The higher value corresponds to a threshold where
insurers generally shy away from insuring (thus any engineering/construction accident likely has a lower probability of occurrence), and 10
−4 is a rate one order of
magnitude above the upper bound of credibility (as engineering/construction accidents are unfortunately well within the credible realm). The second framing requires
calibration of the model based on the data derived causalities (Tables 4.2, 4.3, and
4.4). Finally, the probabilities have to be annualised.
4 Historic Failures “Statistics”
Fig. 4.7 In case (C) the base case is mitigated with M2 = inspections during service life
Fig. 4.8 In case (D) the base case is mitigated with M1 = peer review AND M2 = inspections
By adopting a very simplified approach to CCF it is possible to assume that
insufficient rigour, complacency, conflict of interest, common excessive audacious
approach in M1 and M2 could reduce the expected positive result of any mitigation
to nil.
Four levels of mitigation (Fig. 4.3, i.e., the base case, Fig. 4.6, 4.7, 4.8) were
studied:
(A) Base case with no M1 or M2, depicted in Sect. 4.2.3, Fig. 4.3.
(B) Base case with M1 (Fig. 4.6), i.e., independent peer review (including sensible
RBDM procedures and risk assessment from project inception).
(C) Base case with M2 (Fig. 4.7), i.e., Inspections paired with sensible RBDM
procedures and risk assessment from project inception.
(D) Base case with M1, M2 (Fig. 4.8) (descriptions as above) implemented.
By using ICOLD 1994 and World-wide 1910–2009 data (Tables 4.2 and 4.3) and
the various mitigation variants of the model described above it is possible to evaluate
the probability of failure of a dam under the considered hazard selection for a selected
average life span of 30 years. In order to perform the calculations, one further step is
necessary, as the probability of each hazard hitting a function has to be determined.
The first framing is easy in a professional environment: all those probabilities
lie in the range 10
−2 –10
−4 . The higher value corresponds to a threshold where
insurers generally shy away from insuring (thus any engineering/construction accident likely has a lower probability of occurrence), and 10
−4 is a rate one order of
magnitude above the upper bound of credibility (as engineering/construction accidents are unfortunately well within the credible realm). The second framing requires
calibration of the model based on the data derived causalities (Tables 4.2, 4.3, and
4.4). Finally, the probabilities have to be annualised.