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MindTap Engineering for Das/Sobhan's Principles of Geotechnical Engineering, SI Edition, 9th Edition, [Instant Access], 2 terms (12 months)
9th Edition
ISBN: 9781305971264
Author: Braja M. Das; Khaled Sobhan
Publisher: Cengage Learning US
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Chapter 11, Problem 11.20P
(a)
To determine
Calculate the coefficient of consolidation of the clay for the pressure range.
(b)
To determine
Calculate the time taken for
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A 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 swelling
A 75 mm diameter clay specimen was consolidated in an oedometer under 200 kPa. At the end of consolidation, the void ratio is 0.863 and the specimen thickness is 18.51 mm. When the stress increment of 200 was added to the current vertical stress of 200 kPa, the specimen consolidated to a thickness of 17.56 mm. Assuming that the clay was normally consolidated under the vertical stress of 200 kPa, find the a) coefficient of volume compressibility in (MPa)^-1 and rounded to the 3rd decimal place.b) and the compression index of the clay rounded to the 2nd decimal place.
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.
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- A 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_forwardA standard oedometer test in the laboratory indicated that a 0.02 m thick clay specimen took 0.5 days to undergo 90% primary consolidation. How many days will a 2 m thick layer of identical clay sandwiched between sand layers and subjected to an identical stress increment take to undergo the same?arrow_forwardIn the laboratory test on a clay sample of thickness 25mm, drained at top only, 50% consolidation occurred in 11 minutes. Assume = 0.197, T = 0.405. Find the time required for the corresponding clay layer in the field of 3m thick and drained at top and bottom to undergo 50% consolidation. Also, find the time required to undergo 70% consolidation. TE %3D 70 50arrow_forward
- A site is underlain by a saturated clay layer with thickness = 5m. A sample extracted from the center of the clay layer was recently tested for consolidation parameters. The results indicate that the compression index is 0.33, the recompression index is 0.09, and the void ratio is 1.2. The results also indicate that the layer is normally consolidated. Calculate the preconsolidation stress of the clay. Express your answer in kPa. Note: this is a short problem; read the problem statement carefully. Use unit water weight = 10 kN/m3.arrow_forward2. A layer of compressible clay 6m thick overlies an impervious bedrock and carries an overburden of pervious sand. A large structure founded in the sand causes the stress on every horizontal section of the clay to increase to the same value. In a standard laboratory oedometer consolidation test performed on a 19 mm thick clay specimen, the void ratio changed from 0.765 to 0.750 under a corresponding increase in stress. Consolidation was 70% complete after 30 min. In the field, a) Estimate the settlement of the structure. b) Determine the time taken for one half of the consolidation settlement to take place (Remember the lab test is for a doubly drained specimen.). c) Determine how long it takes for 50% of the settlement to take place at a depth of 0, 2, 3, 5 and 6 m of the clay stratum. d) If the clay were underlain by pervious sand, determine how long it takes for 50% of the settlement to take place at a depth of 0, 2, 3, 5 and 6 m of the clay stratum.arrow_forwardA saturated clay sample in an oedometer is under vertical pressure of 120 kPa and is at a normally consolidated state. The void ratio and the sample height at this stage are 1.21 and 18.40 mm respectively. When the vertical stress was increased to 240 kPa at the end of the consolidation, the thickness of the sample was reduced to 16.80 mm. When the vertical pressure was reduced to the original value of 120 kPa, the sample heaved to a thickness of 16.95 mm. Estimate both the compression index and recompression index of the clay. What would be the reduction in thickness from now if the vertical pressure was increased by 200 kPa? What is the average coefficient volume compressibility during this pressure increment?arrow_forward
- The time for 65% consolidation of a 19-mm clay specimen (drained at top and bottom) in the laboratory is 10 minutes. How long will it take for a 4-m-thick clay layer in the field to undergo 40% consolidation under the same pressure increment? In the field, there is a rock layer at the bottom of the clay.arrow_forwardIn a triaxial test, a specimen of saturated [normally consolidated] clay was consolidated under a chamber confining pressure of 80 kPa. The axial stress on the specimen was then increased through the allowing the drainage from the specimen. The specimen fails when 120 kPa. The pore water pressure at the time was 50 kPa. What is the consolidated undrained friction angle [phi]?arrow_forwardA 10 ft thick clay layer of saturated clay (two-way drainage) under a loading underwent 90% primary consolidation in 400 days. The laboratory test’s specimen will have two-way drainage. Find the coefficient of consolidation of clay for the pressure range. For a 1 inch thick undisturbed clay specimen, how long will it take to undergo 80% consolidation in the laboratory for a similar pressure range?arrow_forward
- 1. The pressure versus void ratio data determined from a consolidation test on an undisturbed clay specimen are as follows: Applied Pressure (kPa) 20 40 80 160 320 640 1280 320 80 20 0 Void Ratio 0.953 0.948 0.938 0.920 0.878 0.789 0.691 0.719 0.754 0.791 0.890 (a) Plot this pressure versus void ratio data on a semi-logarithmic graph. (b) Determine the equations for the virgin compression curve and for the rebound curve for unloading starting at 1,280 kPa. (c) What are the corresponding compression and recompression indices for this soil? (d) Estimate the stress to which this clay has been preconsolidated. (After A. Casagrande.)arrow_forwardThe 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_forwardA specimen of normally consolidated clay was consolidated under a chamber confining pressure of 280kpa for a drained test by how much does the axial stress have to be reduced to cause failure by axial extension?arrow_forward
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