A surcharge and wick drain installation is planned as part of a surcharge program for a highway project undertaken to accelerate the consolidation of a fine-grained soil deposit underlying the...

A surcharge and wick drain installation is planned as part of a surcharge program for a highway project undertaken to accelerate the consolidation of a fine-grained soil deposit underlying the construction area. The wick drains will be approximately 10 mm by 15 mm in cross section. Wicks will be installed in a hexagonal pattern so that each drains an area having an equivalent diameter of 1.25 m (ref. Figure 26); assume an equivalent n ratio to be about 20 for the conditions described. Laboratory tests indicate that the coefficient of consolidation for horizontal drainage is 2.5 m²/month. Calculations indicate that the surcharge loading will cause an eventual total consolidation settlement of 1 m. How long a period will be required for 90 percent of this settlement to occur?