Foundation engineers are often challenged by the existence of soft compressible soils at the construction site. Figure 11.46 shows a soil profile with a silty sand (γ = 15 kN/m3; γ sat = 17 kN/m3) underlain by high-plasticity clay (γ sat = 17 kN/m3) and a peat layer (γ sat = 16 kN/m3), followed by dense sand. To expedite consolidation and minimize future settlement, an additional 2-m-thick fill material, compacted to a unit weight of 19 kN/m3, will be placed on top of the silty sand layer. The plan area of the fill is 10 m x 10 m. The fill load will be left in place for 2 years, after which construction will begin with the fill becoming part of the permanent foundation. Undisturbed samples collected from the clay and organic layers had the following properties:

a. Estimate the total consolidation settlement under the action of the fill load. Consider both the clay and peat layers to be normally consolidated.
b. Estimate the time for 99% primary consolidation in each layer. Are the layers singly or doubly drained? Explain.
c. Estimate the secondary compression in each layer.
d. What will be the total settlement after 2 years?
e. Determine the effective stress at point A three months after the application of the fill load.

C c, (cm2/sec) eo 1.1 0.025 5.9 Layer Ce Clay Peat 0.36 6.6 0.03 0.263 0.003 Fill load (kN/m2) 2 m Silty sand Dense sand