Worst case scale of fluctuation in basal heave analysis involving spatially variable clays

This study explores the phenomenon of a worst case scale of fluctuation (SOF) in basal heave analysis for excavation in spatially variable clays. In the literature, the worst case SOF refers to the SOF where the discrepancy between the mean response from random realizations and the nominal response from a soil mass taking mean properties everywhere is the largest. Random finite element method (RFEM) is adopted to simulate the basal heave factor of safety (FSFEM). It is evident that the mean value of FSFEM can be 10-15 percent smaller than its nominal value at some worst case SOF. It is also shown that the slip circle method (SCM) based on an assumed prescribed slip curve cannot capture the phenomenon of a worst case SOF. However, the SCM can be modified to allow the weakest slip curve in a spatially variable soil mass to be located among a set of statistically independent potential slip curves. This “weakest path” model can reproduce the mean and coefficient of variation of FSFEM approximately without costly simulation when it is appropriately calibrated. In particular, the phenomenon of a worst case SOF can be captured, both qualitatively and quantitatively.