Reliability analysis of unsaturated soil sites based on fundamental period throughout Shiraz, Iran

The soil profile fundamental period is an essential parameter for estimation of site effects on ground motions. However, in most sites, the water table is at a considerable depth and the fundamental period of the unsaturated soil has to be obtained through geotechnical procedures. On the other hand, this parameter is strongly influenced by the uncertainty associated with the site soil properties. In this paper, to assess the influences of non-homogeneity of sites with unsaturated soil, a reliability analysis of fundamental period is presented. For this purpose, a model for predicting unsaturated shear wave velocity using extracted data from six boreholes in three real sites throughout the city of Shiraz in Iran is developed. For the sake of modelling, the soil suction at each depth is calculated from the Soil Water Retention Curve (SWRC) based on the Grain Size Distribution (GSD) of the soil sample. In order for reliability analysis of the sites, constituent variables of the developed model are considered as uncertain and the reliability indices of the fundamental period of the sites boreholes are determined through the Monte Carlo Simulation (MCS) method. The representative reliability indices are combined using the Sequential Compounding Method (SCM) considering the boreholes as parallel components of the system, and the most reliable site is eventually determined.