For drained reclamation, what is the significance of smear zone induced by installation of band drains?

During installation of band drains, smear zones are created in which a zone of soil surrounding the band drains are disturbed. The compressibility of surrounding soils is increased and it results in the reduction of their permeability.

In fact, the surrounding soils are remoulded during the installation process and the effectiveness of band drains is reduced. In essence, for the reduced permeability of soils around band drains, it takes longer time to complete the consolidation process.