Safety margin from characteristic values in settlement calculations of embankments on clay

Settlement calculations in serviceability limit state (SLS) design of embankments require the estimation of characteristic values of soil properties to account for different sources of uncertainty. The upcoming revised version of EN 1997-1:2004 (Eurocode 7) presents a statistically based equation to determine characteristic values of soil properties with the aim of providing a more consistent safety margin. The aim of this study is to quantify the safety margin in settlement calculations using this equation and performing probabilistic analyses. Four different cases of embankments on soft soil with different soil conditions were considered, including significant non-linear stress-strain behaviour. This allowed evaluation of the consistency of the safety margin from statistically derived characteristic values for different soil conditions. Probabilistic analyses were performed using Monte Carlo simulations to determine the statistics of total settlements. The safety margin was then defined based on the distance between the settlement from characteristic values and the mean settlement value of the simulations. The quantified safety margin was not consistent among the cases, which may be related to varying levels of non-linear compressibility and degree of consolidation. Moreover, for some cases, the safety margin might be too conservative for SLS design of embankments.