A silty sand fill 4.5 meters thick and an estimated density of 20 kN/m³ is to be placed over 4.0 m of compressible silty clay. Underlying the clay layer is sandy gravel. The groundwater table is at the surface of the clay layer. Assume, that the compressibility of the fill and sandy gravel are negligible compared to the compressibility of the clay layer. The properties of the normally consolidated silty clay layer are the following: 1.) Initial void ratio e = 1.255; 2.) Compression index C = 0.29; 3.) Re-Compression index C₁ = 0.035; 4.) Saturated density of the silty clay of 17.2 kN/m³; and 5.) Coefficient of consolidation C = 0.79 m²/year; It is desired to perform the following tasks: a.) Subdivide the clay layer into two sub-layers 2.0 m thick each to calculate the surface settlement that the placing of the fill will cause at the end of the consolidation process; b.) Compute the time that it will take to reach 50% and 90% consolidation of the clay layer as well as the settlements that would have occurred at those times; c.) What would be the excess pore water pressure at the mid- point of the first sub-layer (that is, 1.0 meter below the top of the clay layer) two years after the placement of the fill (assume that the fill is placed instantaneously);
A silty sand fill 4.5 meters thick and an estimated density of 20 kN/m³ is to be placed over 4.0 m of compressible silty clay. Underlying the clay layer is sandy gravel. The groundwater table is at the surface of the clay layer. Assume, that the compressibility of the fill and sandy gravel are negligible compared to the compressibility of the clay layer. The properties of the normally consolidated silty clay layer are the following: 1.) Initial void ratio e = 1.255; 2.) Compression index C = 0.29; 3.) Re-Compression index C₁ = 0.035; 4.) Saturated density of the silty clay of 17.2 kN/m³; and 5.) Coefficient of consolidation C = 0.79 m²/year; It is desired to perform the following tasks: a.) Subdivide the clay layer into two sub-layers 2.0 m thick each to calculate the surface settlement that the placing of the fill will cause at the end of the consolidation process; b.) Compute the time that it will take to reach 50% and 90% consolidation of the clay layer as well as the settlements that would have occurred at those times; c.) What would be the excess pore water pressure at the mid- point of the first sub-layer (that is, 1.0 meter below the top of the clay layer) two years after the placement of the fill (assume that the fill is placed instantaneously);
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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Transcribed Image Text:A silty sand fill 4.5 meters thick and an estimated density of 20 kN/m³ is to be placed over 4.0 m of compressible silty clay. Underlying the clay layer is sandy gravel. The groundwater table is at the surface of the clay layer. Assume that the compressibility of the fill and sandy gravel are negligible compared to the compressibility of the clay layer. The properties of the normally consolidated silty clay layer are the following:
1. Initial void ratio \( e_o = 1.255 \);
2. Compression index \( C_c = 0.29 \);
3. Re-compression index \( C_r = 0.035 \);
4. Saturated density of the silty clay of 17.2 kN/m³; and
5. Coefficient of consolidation \( C_v = 0.79 \, \text{m}^2/\text{year} \);
It is desired to perform the following tasks:
a. Subdivide the clay layer into two sub-layers 2.0 m thick each to calculate the surface settlement that the placing of the fill will cause at the end of the consolidation process;
b. Compute the time that it will take to reach 50% and 90% consolidation of the clay layer as well as the settlements that would have occurred at those times;
c. What would be the excess pore water pressure at the midpoint of the first sub-layer (that is, 1.0 meter below the top of the clay layer) two years after the placement of the fill (assume that the fill is placed instantaneously);
d. What would be the vertical effective stress at the midpoint of the second sub-layer (that is, 3.0 meters below the top of the clay layer) after three years of consolidation (same assumptions as in c.); and
e. At one year and six months after placing the fill, the settlement observed in the field is 0.275 m, what would be the value of \( C_v \) that this field measurement would indicate?
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