Reliability

The safe design of a slope requires a factor of safety between 1 and 1.5. A more practical approach to safe design is the probabilistic method, in which each input parameter has a mean and coefficient of variation. This chapter presents some statistical concepts and equations, which are incorporated in LEAME, to determine the reliability of a design. Taylor's expansion applies to simple cases where the factor of safety can be expressed in a closed-form formula. For complex cases involving computer programming, the mean-value first order second moment method (MFOSM) applies. This simplified method is particularly useful in geotechnical engineering. The distribution function used most frequently in geotechnical engineering as a probabilistic model is called the normal or Gaussian distribution. Another distribution used widely in geotechnical engineering is the lognormal distribution.