When an embankment is to be constructed over ground that is too soft or compressible to adequately support the embankment, columns of strong material can be placed in the soft ground to provide the necessary support by transferring the embankment load to a firm stratum. There are numerous types of columns that may be used for this technology (e.g., stone columns, rammed aggregate piers, vibro-concrete columns, deep mixing method columns, continuous flight auger piles, driven piles with or without pile caps, or other types of columns). A load transfer platform or bridging layer may be constructed immediately above the columns to help transfer the load from the embankment to the columns, and thereby permit larger spacing between columns than would be possible otherwise. Load transfer platforms generally consist of compacted soil, and they may include geosynthetic reinforcement. The important details of soil type and geosynthetic reinforcement used in the load transfer platform depend on the design procedure employed. Load transfer platforms are used more often when the spacing between columns is relatively large, which requires higher load carrying capacity from the columns (e.g., vibro-concrete columns, continuous flight auger piles). Load transfer platforms are also used to minimize differential settlement when the embankment height is low. Stone columns and rammed aggregate piers, because of their lower vertical load capacity, are often spaced close enough together that a load transfer platform is not required.
The Collin Group designed one of the first column supported embankment (CSE) projects in the United States in 1994 for a storage tank outside of Philadelphia, PA. Since that first project The Collin Group has been the design engineer of record for over 20 CSE projects and have developed a design methodology for the design of the load transfer platform that is taught to the state departments of transporation as part of the National Highway Institute’s course on Ground improvement.