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Abstract The types of probability distribution of rock and soil parameters have lots of effects on the risk assessment and reliability analysis in geotechnical engineering. So it is a primary work to study rock and soil parameters. Based on the background and physical meaning of various probability distributions，all of them are approximately classified into five series by Bernoulli distribution series，Poisson distribution series，extreme value distribution series，central limit distribution series，and distribution series using for statistical analysis. Subsequently，the factors that affect the uncertainties of rock and soil parameters as random variables are studied. As a result，the central limit distribution series are considered more reasonable for soil parameters. Based on there，the characteristics of normal and lognormal distributions of central limit distribution series are compared in detail. Then，a selection criteria that normal distribution is chosen when coefficient of variation less than 30% and skew coefficient less than 0.025 and lognormal contrarily is recommended. In addition，the distribution which is more suitable for Poisson¢s ratio is also studied. Finally，a statistical case is studied to illustrate the validity of the viewpoint. It is believed that the research results have important reference values for the risk assessment and reliability analysis in geotechnical engineering.
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Received: 29 October 2008
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