Principles of Geotechnical Engineering (MindTap Course List)
9th Edition
ISBN: 9781305970939
Author: Braja M. Das, Khaled Sobhan
Publisher: Cengage Learning
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Chapter 11, Problem 11.16P
(a)
To determine
Calculate the coefficient of volume compressibility for the pressure range.
(b)
To determine
Calculate the hydraulic conductivity in
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2- An undisturbed clay has a preconsolidation pressure of 200 lb/ft. A laboratory consolidation tests yield the
following data:
o' (lb/ft')
e
0.92
3,130
6,270
0.77
a) Determine the void ratio that corresponds to a pressure of 5,800 (Ib/ft).
b) Determine the coefficient of volume compressibility for the pressure range stated.
c) If C, = 1 x 10* in?/sec, determine hydraulic conductivity, k in in/sec corresponding to the average void ratio
within the pressure range.
The laboratory consolidation data for an undisturbed clay specimen are as follows:
e1 = 1.12 P₁ = 90 kPa
e2 = 0.90 P2 = 450 kPa
1. Compute the value of the compression index.
2. Compute the value of the swell index assuming it is equal to 1/6 the value of the compression index.
3. Compute the void ratio for a pressure of 600 kPa.
4. Compute the coefficient of compressibility.
5. Compute the value of the coefficient of volume compressibility.
b. If c, = 2.05 × 10-3 in./sec, determine k in ft/sec corresponding to the
average void ratio within the pressure range.
11.17 The time for 75% consolidation of a 25-mm clay specimen (drained at top
and bottom) in the laboratory is 22 minutes. How long will it take for a
6-m thick clay layer in the field to undergo 55% consolidation under the
same pressure increment? In the field, there is a rock layer at the bottom
of the clay.
Chapter 11 Solutions
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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 swellingarrow_forwardSample of clay isotropically normally compressed to an all round effective pressure of 100 kPa and then allowed to swell back to an effective isotropic pressure of 50 kPa. The sample is then subjected to a standard drained compression test. What is the deviator stress at failure and what is the volumetric strain experienced by the sample at failure? The second sample is subjected to a standard undrained compression test. What are the deviator stress and pore pressure at failure, if there is initially back pressure of 50kPa? Assume that the soil has the following critical state properties: M = 0.95, λ = 0.093, K = 0.035, I = 2.06 and N= 2.118arrow_forwardThe following consolidation test data were obtained from an undisturbed clay specimen. Pressure (kPa) Void ratio 20 0.958 40 0.948 80 0.938 160 0.92 320 0.878 640 0.789 1280 0.691 320 0.719 80 0.754 20 0.791 1 0.89 (a) Plot the void ratio vs. the consolidation pressure curve on semilogarithmic graph paper, and estimate the pre-consolidation pressure o. (b) Determine the compression index C, for the virgin compression and the rebound index C, for the unloading starting at 1280 kPa. (c) Calculate the coefficient of volume compressibility m, for the virgin compression.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_forwardA 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_forward11.11 An undisturbed clay has a preconsolidation pressure of 100 kN/m. A laboratory consolidation tests yield the following data: o' (kN/m?) e 0.92 0.77 150 300 Determine the void ratio that corresponds to a pressure of 450 kN/m?. DCengage Learing 2014arrow_forward
- Subject: Soil Mechanics Please provide a solution and a diagram For a laboratory consolidation test on a clay specimen (drained on both sides) the following results were obtained: Thickness of clay soil= 25 mm; P_1 = 50 kPa; P_2 = 120 kPa; e_1 = 0.92; e_2 = 0.78; Time for 50% consolidation= 2.5 min. Tv = 0.197. Determine the hydraulic conductivity of the clay for the loading range in m/min. a. 1.081 x 10^-3 b. 2.56 x 10^-2 c. 1.31 x 10^-7 d. 1.23 x10 ^-5arrow_forwardRefer to the soil profile shown in figure below. A laboratory consolidation test on the clay gave the results: o'c = 100 kPa Cc = 0.4 Cs = 0.2Cc If the average effective stress on the clay layer increases by 60 kN/m², what would be the total consolidation settlement in cm. Dry sand; e = 0.55 G,= 2.66: Sand G₂ = 2.66 e = 0.48. Clay w 34.78% G₂ = 2.74 Rock 1.5 m. 5 m Water table;arrow_forwardFor a laboratory consolidation test on a clay specimen (drained on both sides) the following results were obtained: Thickness of clay soil= 25 mm; P_1 = 50 kPa; P_2 = 120 kPa; e_1 = 0.92; e_2 = 0.78; Time for 50% consolidation= 2.5 min. Tv = 0.197. Determine the coefficient of consolidation in m2/m. Show free body diagram a.1.081 x 10^-3 b.1.23 x10 ^-5 c.1.31 x 10^-7 d.2.56 x 10^-2arrow_forward
- The coefficient of permeability of a sand at a void ratio of 0.62 is 0.03 cm/s. Estimate the coefficient of permeability at a void ratio of 0.48 using Casagrande equation.arrow_forwardA clay sample was consolidated in a triaxial cell under a backpressure of 50 kPa and cell pressure of 150 kPa. The drainage valve was then closed and the cell pressure was increased to 200 kPa when the pore pressure increased to 98 kPa. What is Skepton’s B-parameter? The above sample was then subjected to a vertical deviator stress, which was increased from zero under undrained conditions. The sample failed when the pore water pressure was 160 kPa and the deviator stress was 70 kPa. What is Skempton’s A-parameter at failure? Assuming the clay is normally consolidated, find the friction angle in terms of effective stresses.arrow_forwardA saturated clay specimen is subjected to a pressure of 240 kN/m2. After the lapse of a time, it is determined that the pore pressure in the specimen is 72 kN/m2. What is the degree of consolidation? Show free body diagram. a.75% b.60% c.70% d.65%arrow_forward
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