Probabilistic nature of cyclic load pore pressure in cohesive soil

Abstract

The probability distribution of cyclic-load-induced pore pressure in contractive cohesive soil is derived based on its dependence on the compressibility of voids. The gamma distribution is established to be the most appropriate by summing exponential changes in the soil compressibility resulting from changes in the condition of the voids. However, since the pore pressure in this soil type is bounded, the upper limit being equal to the undrained strength of the soil and the lower limit near zero, the distribution can be approximated by beta for specified limits. It is established also that the normal distribution can be adopted for the cyclic load pore pressure without loss of accuracy because the gamma distribution approaches the unit normal distribution as the gamma parameter becomes very large. Besides, the gamma distribution has been derived by considering contributions from an infinite number of voids. Therefore the normal distribution, which is generally known as the probability model for sums of random variables when the number of variables is infinitely large, is a fairly reliable approximation of the pore pressure distribution for purposes of practical application.