Bi-Modulus Columns are vertical soil reinforcement elements composed of rigid inclusions topped by a compacted granular material. The upper granular material improves the load transfer and stress distribution from the structure to the rigid inclusions, allowing for an optimum thickness of load transfer platform between the structure and the inclusions.
Bi-Modulus Columns combine the advantages of traditional Stone Columns (i.e. ease of excavation following column installation) without the limitation in very soft soils where a Stone Column solution would not typically be recommended due to the lack of lateral confinement and the risk of column bulging.
The upper granular part of the column is installed before complete setting of the rigid inclusion mortar in order to form a transition zone, composed of a mix between the grout of the inclusion and the stones from the granular tops. In this transition zone, an optimal concentration and transfer of the surface loads to the underlying competent soil layer can be developed.
- A Bi-Modulus Column system generally results in a reduced thickness of load transfer platform and therefore minimizes the quantity of imported granular backfill;
- Bi-Modulus Columns can be used to overcome complex rigid inclusion cut-off problems (i.e. deep cut-off with highly variable elevations) when the surrounding soils are too soft for a more classical stone column design;
- The use of Bi-Modulus Columns can be an efficient alternative to a load transfer mat under shallow footings combined with rigid inclusions for projects with stringent seismic design requirements