A system of prefabricated vertical drains with surcharge preloading is an effective method for promoting radial drainage and accelerated soil consolidation. A piecewise technique is employed to analyse the radial consolidation in a multilayer soil system to include (i) the effect of soil downdrag and (ii) a smear zone having linearly varying soil permeability. The effect of soil dragged down from the upper soil layer into the lower layer has been analysed in terms of the time required for consolidation. It can be seen that the consolidation of the multilayer soil depends on smear zone characteristics, the permeability ratio between upper and lower soil layers, penetration depth, and drain spacing. Design procedures are described with the help of an example.
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