Probability distribution of strength under uniaxial stress was examined on the basis of published data. It was found that strength followed the Weibull distribution. Shape parameter or coefficient of variation in air-dried condition gave good agreement with that in water-saturated condition.
Probability distribution of failure time in creep testing was also examined on the basis of published data. Failure time also followed the Weibull distribution. Shape parameter of creep life was found to agree well with that of strength.
Probability distribution of strength under triaxial stress field is considered to be important, however, only a few studies have been published. In this study, a tuff and a mudstone were tested under triaxial stress. It was found that strength followed the Weibull distribution. Shape parameters of tuff by this study and andesite by Yamaguchi did not change so much with confining pressure, however, that of mudstone increased notably.
The experimental data were discussed from not only deterministic but also stochastic points of view.