11.C.1 Foundation engineers are often challenged by the existence of soft compress- sand (y 17 kN/m: Yat 19.2 kN/m) underlain by high plasticity clay ible soils at the construction site. Figure 11.49 shows a soil profile with a silty (Yat 18.8 kN/m) and a peat layer (Ya 15 kN/m), followed by dense sand. To expedite consolidation and minimize future settlement, an additional 1.75-m thick fill material, compacted to a unit weight of 20.1 kN/m, will be placed on top of the silty sand layer. The plan area of the fill is 8 m x 8 m. The fill load will be left in place for 18 months, after which construction will begin with the fill becoming part of the permanent foundation. Undisturbed samples col- lected from the clay and organic layers had the following properties: Layer Clay Peat C 0.31 C 0.048 c, (cm/sec) e 7.2 0.273 0.006 0.029 1.08 6.4 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 up to end of 18 months. d. What will be the total settlement after 18 months? e. What is the remaining excess pore water pressure at point A two months after the application of the fill load? Fill load (kN/m) f. Determine the effective stress at point A two months after the applica- tion of the fill load. g. A piezometer was installed at point A to monitor the pore water pres- sure. What should be the piezometer reading (piezometer) two months after the fill load was applied? 1.5 m 1.5 m Silty sand 3.2 m 4 m Clay A Piezometer 1.8 m Peat Figure 11.49 Dense sand GWT