Principles of Foundation Engineering (MindTap Course List)
9th Edition
ISBN: 9781337705028
Author: Braja M. Das, Nagaratnam Sivakugan
Publisher: Cengage Learning
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Chapter 15, Problem 15.2P
To determine
Check whether the in situ soil is normally consolidated or over consolidated.
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3.
A stratum of normally consolidated clay is 25 feet thick and the water content is
measured as 50% (Gs=2.7). Consolidation tests on undisturbed samples of the clay indicate Ce
= 0.68. On top of the clay is 5 feet of sand with a total unit weight of 120 pcf. To build a
parking lot, 8 feet of fill is now placed on top of the sand. Tests on the fill indicate that the
average water content is 10% and the average dry unit weight is 115 pef. The water table is
located 2 ft below the ground surface. Calculate the settlement of the clay due to the added
weight of the fill. Treat the clay as one layer and compute the stresses and change in void ratio
at mid-depth in the clay.
A 7 ft layer of clay is buried beneath a 10 ft layer of compact granular soil. Compact sand underlies the clay. The layer of granular soil is composed of material having a unit weight of 130 pcf. The clay unit weight is 105 pcf. A lab consolidation test on a sample of the clay indicates a compression index of 0.40 and a natural void ratio of 1.30. A planned building loading will cause a 550 psf stress increase at the middle of the clay layer.
What amount of primary consolidation occurs in the clay layer for the indicated conditions?
How much primary consolidation of the clay layer would result if the groundwater table was at the ground surface and all other conditions are the same?
How much primary consolidation would occur if the clay was an overconsolidated material, the past maximum pressure was 2,000 psf, and the swell index Cs is 0.10 and the water table is deep.
Chapter 15 Solutions
Principles of Foundation Engineering (MindTap Course List)
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- The water content of a sample of saturated soil at a mean effective stress of 10 kPa is 85%. The sample was isotropically consolidated with a mean effective stress of 150 kPa. At the end of the consolidation, the water content was 50%. The sample was then isotropically unloaded to a mean effective stress of 100 kPa, and the water content increased by 1%. Given: Gs = 2.7, o'cs = 25°. a) Calculate and K. 10 b) Determine the failure stresses (p'f and gf) under CU test and CD test for the conditions.arrow_forwardThe consolidation test of a clay sample taken from a 2 m thick normally consolidated clay soil layer has been conducted and the results are shown in the table below. The average overburden stress of the clay soil layer is 50 kPa, What would the total settlement (mm) be if an additional 100 kPa loading is applied over a large area on the top of the clay layer? (Hint: void ratio is related to the sample volume) P(kPa) 0 50 100 200 400 e 0.850 0.760 0.710 0.650 0.640arrow_forwardAn oedometer test on a saturated clay soil gave the following results: Cc = 0.2 and Cs = 0.04. The in-situ vertical effective stress in the field is 130 kPa. A building foundation will increase the vertical stress in the center of the clay by 150 kPa. The thickness of the clay layer is 2 m and its water content is 28%. Calculate the primary consolidation settlement of the clay layer in the field if: a). OCR = 4.5; b). OCR = 1.5.arrow_forward
- A CU triaxial test was carried out on a silty clay that was isotopically consolidated using a cell pressure of 125 kPa. The following data were obtained: Axial load (kPa) 0 5.5 11.0 24.5 28.5 35.0 50.5 85.0 105.0 120.8 Axial strain, E₁ (%) 0 0.05 0.12 0.29 0.38 0.56 1.08 2.43 4.02 9.15 Au (kPa) 0 4.0 8.6 19.1 29.3 34.8 41.0 49.7 55.8 59.0 (a) Plot the deviatoric stress vs. axial strain and excess porewater pressure vs. axial strain, respectively. (b) Determine the undrained shear strength (su). (Note: we assume that the sample reaches failure). (c) Determine the total principal stresses (0₁,03) and the effective principal stresses (0₁, 03') at the failure, respectively.arrow_forwardQuestion attachedarrow_forwardConsolidation problemarrow_forward
- Thanksarrow_forwardThe initial void ratio of the clay layer isarrow_forwardA consolidated undrained triaxial test was performed on a normally consolidated clay with a critical state friction angle of 230. After an initial isotropic consolidation at a cell pressure of 50 kPa, drainage was turned off, the cell pressure was increased to 85 kPa, and the sample was loaded to ultimate conditions. A pore pressure of 55 kPa was measured at ultimate state. What value of major principal total stress was measured at the ultimate state?arrow_forward
- During a consolidation test, an increment pressure of 153 kN/m2 was applied to a sample of saturated clay initially 20 mm thick. When equilibrium was reached the thickness of the sample was reduced to 18.3 mm. The pressure was then removed and the sample was allowed to expand. The final thickness was recorded as 19.3 mm and the final moisture content was 30.1%. If the specific gravity of the particles is 2.65 and the sample was saturated throughout the test, determine the following: 8.1 Voids ratio before and after consolidation. 8.2 The average coefficient of volume change over the range of pressure appliedarrow_forwardA clay sample underwent a consolidation test in the lab. The clay specimen has drainage on both sides and a height of 25.4 mm. Assume that the clay sample's preconsolidation pressure was less than 150 kPa prior to the consolidation test. The void ratio was 0.96 when the applied effective vertical pressure was 150 kPa. When the vertical effective pressure increased from 150 to 220 kPa, the void ratio at the end of consolidation and compression was 0.88. It was discovered that the sample needed 3 minutes to consolidate by 30%. Following the consolidation test, a swelling/unloading test was conducted, in which the vertical effective stress was lowered from 220 to 150 kPa and the end-of-swelling void ratio was determined to be 0.9. Required a. The compression index of the clay b. The swelling index of the clay C. The height of the clay sample at the end of compression d. The coefficient of consolidation of the clay e. The final height of the clay sample at the end of swellingarrow_forwardBelow are results from three unconsolidated undrained triaxial tests performed on a fully saturated clay specimen: Test No. 1 2 Minor principal stress (psi) Major principal stress at failure (psi) 10 25 33 22 37 45 Moisture content = 21 % Determine: a) Void ratio (e) of the soil. You may use eS = wG_ (assume Gs = 2.70) %3D b) Deviatory stress at failure for each test trial c) Shear strength parameters (cu and ø). Hint: Sketch the Mohr's circles for the three trials. 3.arrow_forward
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