Reliability analysis of consolidation settlement in clay subsoil using FOSM and Monte Carlo simulation

Abstract

The settlement of ground-supported transportation infrastructures may vary greatly depending on the uncertainties related to compressibility properties and overconsolidation of clay. These uncertainties can be considered systematically by means of reliability analysis where the probability distribution of consolidation settlement is evaluated. Hence, this paper applies two well-known reliability methods, first-order second-moment method (FOSM) and Monte Carlo simulation, to various theoretical consolidation scenarios and three case studies of test embankments founded on normally consolidated (NC) or overconsolidated (OC) clay subsoil. The aim is to assess the accuracy and limitations of FOSM when applied to estimate the mean, the standard deviation, or the upper 95th percentile of the settlement. According to the results, the accuracy of FOSM is adequate for most serviceability limit state (SLS) purposes if the clay is normally consolidated. On the other hand, large relative errors may be introduced for OC clays where the relative contribution of OC and NC strains creates a strongly non-linear problem. It is concluded that FOSM, combined with second-order mean, may be applied to preliminary settlement estimation of OC clays. However, in the actual SLS verification with certain target reliability, Monte Carlo simulation should be used to ensure high enough accuracy.