The development of quantitative risk assessment (QRA) methodologies has advanced to such a state that it is now a practical risk management tool in geotechnical engineering. Pilot applications of QRA have shown great promise and it has contributed to addressing questions that would otherwise be very difficult to answer using conventional techniques. Resistance against the more widespread use of QRA is real and this is partly due to myths about the technique. The essence is risk-based thinking, be it under a quantitative or qualitative framework. The geotechnical community stands to gain by integrating risk-based thinking and methodologies into current geotechnical practice. This integration will better align the geotechnical profession with many of the other engineering fields that practise risk management in a more explicit manner.


In geotechnical engineering, empirical rules based on precedents are commonly relied upon to solve practical problems. Modelling the full range of factors involved in a real problem in detail is, nearly always, too complicated and not credible. Fortunately, only some of the factors tend to be major in a given problem and these can usually be characterized by indices from standard tests. It is generally deemed that one can obtain a good enough estimate for engineering purposes by discounting the minor factors as unimportant and the extreme factors as unlikely. This pragmatic approach has generally served the geotechnical profession well. However, unpleasant surprises do occur from time to time. "Minor" factors can turn out to be major, and "extreme" events can occur more frequently than expected. Geotechnical failures are not a rarity, and sometimes occur in a disastrous manner. What was judged to be unimportant may actually be very important, at least for the combination of circumstances at hand which might not have been foreseen (but were not necessarily unforeseeable).

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