An investigation of progressive failure of geosynthetic reinforced deep cement mixed column supported embankments

Deep cement mixed columns are widely used to support highway embankments constructed on soft compressible ground. In current design practice, it is assumed that the performance of Geosynthetic Reinforced Column Supported (GRCS) embankments is similar to that of pile supported embankments and the constitutive behavior of DCM columns is simulated assuming elastic perfectly plastic behavior. However, cement admixed soils exhibit strain softening behavior due to progressive failure of cementation bonds beyond yielding and classical constitutive models such as Modified Cam Clay and Mohr-Coulomb are inadequate to describe this behavior. Therefore, during the design process, settlements may be underestimated and the ability of the embankment to resist deformations is overestimated, leading to unsafe designs. This paper investigates the behavior of DCM column supported embankments, when the progressive failure of the DCM columns is incorporated in the analysis. Results show that the maximum settlements of columns and the clay layer, and the maximum strain and tension in the geosynthetic layer obtained including the progressive failure, are significantly higher than those obtained without allowance for progressive failure of cement admixed soils. The finite element analysis results clearly illustrate the bending failure mode due to progressive softening of the cement admixed soils, including the plastic hinge development at the locations of the maximum bending moment within columns. Consequently this study establishes the main differences between DCM-column supported and pile-supported embankments.