What are the potential problems of smear around vertical drains?

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Smear zones are generated during the installation of vertical drains in which the zone of soils surrounding the band drains are disturbed. Soils in the smear zones are remoulded during the installation process and the effectiveness of band drains is reduced. For instance, the compressibility of surrounding soils is increased and this brings about the reduction of their permeability. In essence, with the reduced permeability of soils around band drains, it takes longer time to complete the consolidation process.

To prevent the formation of smear zones, the raising and lowering of mandrel during drain installation should be minimized. Moreover, soil disturbance can be controlled by avoiding the use of vibratory hammers which serve to drive the drains into the ground.

Smear zones in band drain


This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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