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 11.15P
(a)
To determine
Calculate the degree of consolidation in the middle of the clay layer.
(b)
To determine
Calculate the excess pore water pressure in the middle of the clay layer.
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Redo Problem 11.6 using the weighted average method [Eq. (11.68)] to calculate the stress increase in the clay layer.
Problem 11.6
Refer to Figure 11.43. Considering the soil to be a uniform clay layer, estimate the primary consolidation settlement due to
the foundation load. Given:
P = 150 kN; B = 3 m; L = 3 m; D, = 1.5 m; H = 8 m; e = 0.7; G, = 2.72; and
LL = 42. Assume that the clay is normally consolidated, and the groundwater
P
table is at the foundation level. Use Ao =
BL
Figure 11.43
Foundation
BxL
Ao
Soil
H, = Poisson's ratio
E, = modulus of elasticity H
%3D
Rock
Figure 11.43
©Cengage Leam ing 2014
Solve the following problems using the figure.
1. Calculate the ultimate settlement of the clay layer.
2. Calculate the excess pore pressure (ue) and the
effective stress at the midpoint of the clay layer
after 3 years.
10'
Fill, y = 118b/³
Sand, y 109 lb/ft³
Sand, Ysat 114 lb/ft³
eo = 1.1
Cc = 0.25
C₁ = 7 ft²/yr
C₁ = 0.06
clay
14'
N.C
Ysat = 122 lb/ft³
sand
8.
For the previous problem, report the predicted settlement after 365 days.
3. Create a plot (or plots) in a spreadsheet showing
the hydrostatic pressure in the clay with depth and the excess pore pressure (ue) with
depth after 3 years and the combined pore pressure after 3 years. (This is similar to an
example worked in class)
4.
Calculate the average percentage of consolidation (U%) for the clay layer after 3 years.
5. How long will it take for 80% of the ultimate settlement of the clay layer to take place?
6. Assume thin layers of drainable sand are present every two feet within the clay so it is
actually five clay layers that…
9.18 Fig. P9.18 shows the soil profile at a site for a proposed office building. It
is expected that the vertical stress at the top of the clay will increase by 150
kPa and at the bottom by 90 kPa. Assuming a linear stress distribution
within the clay, calculate the consolidation settlement. [ Hint: You should
divide the clay into five equal layers, compute the settlement for each layer,
and then find the total settlement.] Groundwater level is at the top of the
clay layer. An oedometer test on a sample of the clay revealed that the time
for 90% consolidation on a 20 mm thick sample occurred in 40 minutes.
The sample was drained on the upper and lower boundaries. How long will
it take for 50% consolidation to occur in the field?
w = 23%
5 m
S = 90%
Sand
w = 40%
10 m C=0.3
OCR = 1
Clay
Impervious rock
FIGURE P9.18
Chapter 11 Solutions
Principles of Geotechnical Engineering (MindTap Course List)
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- 8.15 Estimate the consolidation settlement of the clay layer shown in Figure P8.13 using the results of Problem 8.13.arrow_forwardIn a normally consolidated clay specimen, the following data are given from the laboratory consolidation test. e₁ = 1.10 σ= 65.0 kN/m² €₂ = 0.85 o₂ = 240.0 kN/m² a. Find the compression index C. b. What will be the void ratio when the next pressure incre- ment raises the pressure to 460.0 kN/m²?arrow_forwardRefer to the soil profile shown in Figure P2.12. The clay is normally consolidated. A laboratory consolidation test on the clay gave the results: If the average effective stress on the clay layer increase by 50 kN/m2.a. What would be the total consolidation settlement?b. If Cv = 9.36 x 10-4 cm2/sec, how long will it take for half the consolidation settlement to take place?arrow_forward
- 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.arrow_forward4. In a consolidated-drained triaxial test on a clay that is normally consolidated, the results are as follows: O3 = 15 lb/in 2 (Aoa)f = 11 lb/in? (Aua)f = 7.2 lb/in? a) Determine the consolidated-undrained friction angle. %3D b) Calculate the drained friction angle.arrow_forwardRefer to Figure 11.41. Given that B =1 m, L = 3 m, and Q = 110 kN, the soil characteristics given in the figure are Cs = 1/5 Cc, Ꝺ’c= 40 kN/m2. Field monitoring indicated that the foundation settlement was 19 mm during the first 12 months. a. Estimate the average stress increase in the clay layer due to the applied load. b. Estimate the primary consolidation settlement. c. What is the degree of consolidation after 12 months? d. Estimate the coefficient of consolidation for the pressure range. e. Estimate the settlement in 24 months. Answer must be: A. 6.33 B. 32.82 C. 57.89 D. 0.0013 E. 25.66arrow_forward
- The following are the results of a consolidation test on a sample of a clayey soil. • Plot the e-log o curve. • Determine the pre-consolidation pressure. • Calculate the compression index, Ce and the ratio of C; /Ce. Pressure, o' (kN/m?) 1.113 25 1.106 50 1.066 100 0.982 200 0.855 400 0.735 800 0.63 1600 0.66 800 0.675 400 0.685 200arrow_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_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
- 7.2 A specimen of normally consolidated clay (= 28°) was consolidated under a chamber-confining pressure of 280 kN/m². For a drained test, by how much docs the axial stress have to be reduced to cause failure by axial extension? 1 7.3 A normally consolidated clay specimen (= 31°) was consolidated under a chamber-confining pressure of 132 kN/m². Failure of the specimen was caused by an added axial stress of 158.1 kN/m in an undrained condition. Determine &u, Af and the pore water pressure in the specimen at failure. >arrow_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_forwardQ#3: For a normally consolidated clay layer in the field, the following values are given. Thickness of clay layer = 2.6 m Compression index = 0.28 Average effective pressure on clay layer 127 KN/m² Secondary compression index = 0.02 Δσ’ = 46.5 KN/m² Void ratio = 0.8 Time of Primary settlement = 1.5 years What is the total consolidation of the clay layer five years after the primary consolidation settlement?arrow_forward
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