Why failures in geotechnics are less frequent than predicted?

One of the most important unresolved problems in geotechnical risk assessment is that “Why are failures less frequent than our reliability studies predict?” In order to answer this question the safety requirements of Eurocode 7 have been investigated. It has been concluded that the safety of soil mechanics parameters, defined by probability requirements, does not included in the calculated Overall Factor of Safety, which represents the overall reliability of a geotechnical design. Method, how to convert the probability requirements to factor of safety is proposed. Incorporating the probabilistic safety of soil mechanics parameters into the Overall Factor of Safety results in a reliable estimation for the failure of geotechnical structures.