Stability of column-supported embankments

Column-supported embankments have a great potential for application in the coastal regions of Virginia, where highway embankments are often constructed on soft ground. The columns can be driven piles, vibro-concrete columns, deep-mixing-method columns, stone columns, or other suitable types. Column-supported embankments are used to accelerate construction by eliminating consolidation times that are needed for preloading and surcharging operations associated with conventional prefabricated vertical drains. This study has resulted in a development of new numerical stress-strain analyses to evaluate the stability of embankments supported on columns installed by deep mixing method. Such analyses reflect the multiple realistic failure mechanisms that can occur when strong columns are installed in weak soil. Detailed recommendations for performing numerical analyses are presented. The findings are also expected to apply to vibro-concrete columns, because they, like deep-mixing-method columns, are strong in compression but weak in bending and tension. The study also recommends the use of reliability analyses in conjunction with the stability analysis. Reliability analyses are necessary, because deep-mixed materials can be highly variable and because typical variations in the strength of the surrounding clay can induce abrupt tensile failure in columns. Additional benefit of the reliability-based design is that it permits rational development of statistically-based specifications for constructing deep-mixed materials.