A long highway embankment, having the cross-section shown in Figure 2, is to be rapidly constructed at a site. The unit weight of the embankment material is 18.85 kN/m³. The soil profile at the site consists of a 3 m thick layer of coarse sand underlain by an 8 m thick layer of overconsolidated soft silty clay. 2.5 4.0m 4 4.0 m Coarse sand 2.0 m piezometer 2.0 m Soft silty clay 3.0 m 2.5 10.0 m Impermeable layer 3.0 m 8.0 m Figure 2: Cross-section of a long embankment instrumented with three piezometers. From the results of laboratory tests, the saturated unit weight of the coarse sand is 16.5 kN/m³. Based on the results of tests performed on a sample from the mid-depth of the soft silty clay layer, the saturated unit weight of the coarse sand is 17.0 kN/m³, the initial void ratio (eo) is equal to 2.30, the swell/re-compression index (Cr) is equal to 0.055, the compression index (C) is equal to 0.245, and the coefficient of consolidation (c) is 20 m²/yr. Finally, it is estimated that the overconsolidation ratio (OCR) is 2.50. a) Compute the vertical effective stress at the mid-depth of the soft silty clay layer prior to the placement of the embankment. b) Estimate the preconsolidation stress (σp) for a sample from the mid-depth of the soft silty clay layer. c) Compute the increment in vertical total stress (Aσ,) at the mid-depth of the soft silty clay layer along the centerline of the embankment due to its construction. Consult Section 7.8 in the textbook (also see Figure 7.13) or use the equations presented in lecture. d) Compute the ultimate primary consolidation settlement (sc) of the mid-depth of the silty clay layer along the centerline of the embankment. e) What is the time required to reach 50% of the ultimate primary consolidation settlement. f) Compute the amount of primary consolidation settlement after 120 days. g) After one year, what would be the excess pore pressure measured by the three electric piezometers that were installed in the soft silty clay layer?

A long highway embankment, having the cross-section shown in Figure 2, is to be rapidly constructed at a site. The unit weight of the embankment material is 18.85 kN/m³. The soil profile at the site consists of a 3 m thick layer of coarse sand underlain by an 8 m thick layer of overconsolidated soft silty clay. 2.5 4.0m 4 4.0 m Coarse sand 2.0 m piezometer 2.0 m Soft silty clay 3.0 m 2.5 10.0 m Impermeable layer 3.0 m 8.0 m Figure 2: Cross-section of a long embankment instrumented with three piezometers. From the results of laboratory tests, the saturated unit weight of the coarse sand is 16.5 kN/m³. Based on the results of tests performed on a sample from the mid-depth of the soft silty clay layer, the saturated unit weight of the coarse sand is 17.0 kN/m³, the initial void ratio (eo) is equal to 2.30, the swell/re-compression index (Cr) is equal to 0.055, the compression index (C) is equal to 0.245, and the coefficient of consolidation (c) is 20 m²/yr. Finally, it is estimated that the overconsolidation ratio (OCR) is 2.50. a) Compute the vertical effective stress at the mid-depth of the soft silty clay layer prior to the placement of the embankment. b) Estimate the preconsolidation stress (σp) for a sample from the mid-depth of the soft silty clay layer. c) Compute the increment in vertical total stress (Aσ,) at the mid-depth of the soft silty clay layer along the centerline of the embankment due to its construction. Consult Section 7.8 in the textbook (also see Figure 7.13) or use the equations presented in lecture. d) Compute the ultimate primary consolidation settlement (sc) of the mid-depth of the silty clay layer along the centerline of the embankment. e) What is the time required to reach 50% of the ultimate primary consolidation settlement. f) Compute the amount of primary consolidation settlement after 120 days. g) After one year, what would be the excess pore pressure measured by the three electric piezometers that were installed in the soft silty clay layer?

Principles of Foundation Engineering (MindTap Course List)

9th Edition

ISBN:9781337705028

Author:Braja M. Das, Nagaratnam Sivakugan

Publisher:Braja M. Das, Nagaratnam Sivakugan

Chapter2: Geotechnical Properties Of Soil

Section: Chapter Questions

Problem 2.8P

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Transcribed Image Text:A long highway embankment, having the cross-section shown in Figure 2, is to be rapidly constructed at a site. The unit weight of the embankment material is 18.85 kN/m³. The soil profile at the site consists of a 3 m thick layer of coarse sand underlain by an 8 m thick layer of overconsolidated soft silty clay. 2.5 4.0m 4 4.0 m Coarse sand 2.0 m piezometer 2.0 m Soft silty clay 3.0 m 2.5 10.0 m Impermeable layer 3.0 m 8.0 m Figure 2: Cross-section of a long embankment instrumented with three piezometers. From the results of laboratory tests, the saturated unit weight of the coarse sand is 16.5 kN/m³. Based on the results of tests performed on a sample from the mid-depth of the soft silty clay layer, the saturated unit weight of the coarse sand is 17.0 kN/m³, the initial void ratio (eo) is equal to 2.30, the swell/re-compression index (Cr) is equal to 0.055, the compression index (C) is equal to 0.245, and the coefficient of consolidation (c) is 20 m²/yr. Finally, it is estimated that the overconsolidation ratio (OCR) is 2.50. a) Compute the vertical effective stress at the mid-depth of the soft silty clay layer prior to the placement of the embankment. b) Estimate the preconsolidation stress (σp) for a sample from the mid-depth of the soft silty clay layer.

c) Compute the increment in vertical total stress (Aσ,) at the mid-depth of the soft silty clay
layer along the centerline of the embankment due to its construction. Consult Section 7.8 in
the textbook (also see Figure 7.13) or use the equations presented in lecture.
d) Compute the ultimate primary consolidation settlement (sc) of the mid-depth of the silty
clay layer along the centerline of the embankment.
e) What is the time required to reach 50% of the ultimate primary consolidation settlement.
f) Compute the amount of primary consolidation settlement after 120 days.
g) After one year, what would be the excess pore pressure measured by the three electric
piezometers that were installed in the soft silty clay layer?

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