Prefabricated vertical drains are often used to accelerate the consolidation and to gain strength in soft clayey soils. The consolidation process depends on several uncertain parameters including the coefficients of consolidation and coefficients of permeability in vertical and horizontal directions and the discharge capacity of the vertical drains. A sensitivity analysis of the degree of consolidation to these uncertain parameters is presented for clayey deposits. Results of the analysis suggest that the most important uncertain parameter that affects the consolidation process is the horizontal coefficient of consolidation. The implication of this uncertain parameter in the design of prefabricated vertical drains for soil improvement is discussed. Two approaches are proposed for selecting drain spacing employing a design value of the horizontal coefficient of consolidation. One of the approaches is probability based and the other is minimum expected cost based. [References: 20]
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