Significance of spatial variability of deep cement mixed columns on reliability of column-supported embankments

The spatial variability of mechanical properties of deep cement mixed (DCM) soil leads to uncertainty in performance of DCM column-supported embankments. While adequate safety levels can be achieved using a large factor of safety in a deterministic design, a reliability assessment helps to find an optimum safety level for the design by managing variability parameters. However, only few studies have been conducted on the performance of DCM column-supported embankments considering the variability of mechanical properties of columns. None of these studies have considered the strain-softening behavior of DCM columns along with the strength variability. This study investigates the reliability of a DCM column-supported embankment considering the spatial variability of mechanical properties and strain-softening behavior. Compressive strength, elastic modulus, and cohesion of DCM soil were considered as stochastic parameters in this study. The analysis was carried out using Monte Carlo method assuming three different cases of spatial variability. The reliability response of the embankment to changing coefficient of variation (COV), mean compressive strength, and the spatial correlation length are discussed. Results demonstrate that the reliability performance level of the embankment can be conservatively predicted by considering the variability of mean DCM column strength without considering the spatial variability. Based on the results of this study, a method is proposed to determine the overdesign factor required to achieve a target reliability for the embankment.