Principles of Geotechnical Engineering-149-151
Principles of Geotechnical Engineering-149-151
Principles of Geotechnical Engineering-149-151
Problems
4.1 During Atterberg limit tests in the soil mechanics laboratory, the students
obtained the following results from a clayey soil.
Liquid limit tests:
Number of Moisture
blows, N content (%)
14 38.4
16 36.5
20 33.1
28 27.0
Plastic limit tests: Students conducted two trials and found that PL 5 17.2%
for the first trial and PL 5 17.8% for the second trial.
a. Draw the flow curve and obtain the liquid limit.
b. What is the plasticity index of the soil? Use an average value of PL from
the two plastic limit trails.
4.2 Refer to the soil in Problem 4.1. A second group of students conducted only
one test and found that the groove on the soil sample closed 12.5 mm when
N 5 21 and w 5 30.4%. Estimate the liquid limit by the one-point method.
4.3 Refer to the soil in Problem 4.1.
a. Determine the flow index.
b. Determine the liquidity index of the soil if the in situ moisture content is 21%.
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Problems 125
4.4 Results from a liquid limit test conducted on a soil are given below.
Number of Moisture
blows, N content (%)
12 35.2
19 29.5
27 25.4
37 21
Number of Moisture
blows, N content (%)
15 39.5
21 37.9
29 36.4
38 35.1
Cone Moisture
penetration, d content
(mm) (%)
13 26.3
19 31.9
26 39.3
31 42.6
4.8 Refer to the same soil in Problem 4.7. A single test was conducted with
the fall cone device and the following results were obtained: d 5 17 mm and
w 5 28.5%. Using Eqs. (4.5), (4.6), and (4.7), estimate the liquid limit by the
one-point method.
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126 Chapter 4 | Plasticity and Structure of Soil
4.9 Refer to the liquid limit determined in Problem 4.5 using the percussion cup
method (ASTM 4318). Estimate the liquid limit for the same soil if the fall
cone method (BS 1377) were used. Use Eq. (4.8).
4.10 During a shrinkage limit test, a 19.3 cm3 saturated clay sample with a mass
of 37 g was placed in a porcelain dish and dried in the oven. The oven-dried
sample had a mass of 28 g with a final volume of 16 cm3. Determine the shrink-
age limit and the shrinkage ratio.
4.11 The following data were recorded during a shrinkage limit test on a clay soil
pat: Vi 5 20.6, Vf 5 13.8 cm3, M1 5 47.5 g, and mass of dry soil, M2 5 34.6 g.
Determine the shrinkage limit and the shrinkage ratio.
4.12 In a shrinkage limit test, a sample of saturated clay was dried in the oven.
The dry mass of the soil was 22.5 g. As shown in Figure 4.13, when the
moisture content is at the shrinkage limit, the soil reaches a constant total
volume, Vf . If Vf = 10.3 cm3, calculate the shrinkage limit of the soil. Given:
Gs 5 2.72
4.C.2 Liquidity index, LI, defined by Eq. (4.26), can indicate probable engineering
behavior depending on the natural or current state of moisture content. For
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