
Three groups of students from the
(a)
(b)
Figure 2.35 (a) Soil-aggregate stockpile; (b) sieve analysis (Courtesy of Khaled Sobhan, Florida Atlantic University, Boca Raton, Florida)
a. Determine the coefficient of uniformity and the coefficient of gradation for Soils A, B, and C.
b. Which one is coarser: Soil A or Soil C? Justify your answer.
c. Although the soils are obtained from the same stockpile, why are the curves so different? (Hint: Comment on particle segregation and representative field sampling.)
d. Determine the percentages of gravel, sand and fines according to Unified Soil Classification System.
(a)

Calculate the coefficient of uniformity
Answer to Problem 2.1CTP
The uniformity coefficient of soil A is
The coefficient of gradation of soil A is
The uniformity coefficient of soil B is
The coefficient of gradation of soil B is
The uniformity coefficient of soil C is
The coefficient of gradation of soil C is
Explanation of Solution
Sketch the grain size distribution curve for soils A, B, and C as shown in Figure 1.
Refer to Figure 1.
For soil A:
The diameter of the particle corresponding to
The diameter of the particle corresponding to
The diameter of the particle corresponding to
For soil B:
The diameter of the particle corresponding to
The diameter of the particle corresponding to
The diameter of the particle corresponding to
For soil C:
The diameter of the particle corresponding to
The diameter of the particle corresponding to
The diameter of the particle corresponding to
Calculate the uniformity coefficient
For soil A:
Substitute
Hence, the uniformity coefficient for soil A is
For soil B:
Substitute
Hence, the uniformity coefficient for soil B is
For soil C:
Substitute
Hence, the uniformity coefficient for soil C is
Calculate the coefficient of gradation
For soil A:
Substitute
Hence, the coefficient of gradation for soil A is
For soil B:
Substitute
Hence, the coefficient of gradation for soil B is
For soil C:
Substitute
Therefore, the coefficient of gradation for soil C is
(b)

State which of the soil is coarser from soil A and C.
Answer to Problem 2.1CTP
Soil A is coarser than soil C.
Explanation of Solution
Refer to part (a).
The uniformity coefficient of soil A is
The uniformity coefficient of soil C is
The percent of soil finer than
The percent of soil finer than
Hence, a higher percentage of soil C is finer than soil A.
Hence, soil A is coarser than soil C.
(c)

Explain the reason for curve different of soil A, B and C if it is obtained from same stockpile.
Explanation of Solution
The particle-size distribution curve shows the range of particle sizes present in a soil and the type of distribution of various-size particles.
Refer to Figure 1.
Particle separation of coarser and finer particles may take place in aggregate stockpiles. This makes representative sampling difficult.
Therefore, the particle-size distribution curve is different for soils A, B, and C.
(d)

Calculate the percentages of gravel, sand, and fines according to the Unified Soil Classification System.
Answer to Problem 2.1CTP
The percentage of gravel for soil A is
The percentage of sand for soil A is
The percentage of fines for soil A is
The percentage of gravel for soil B is
The percentage of sand for soil B is
The percentage of fines for soil B is
The percentage of gravel for soil C is
The percentage of sand for soil C is
The percentage of fines for soil C is
Explanation of Solution
Refer to Figure 1.
For soil A.
The percent passing through
The percent passing through
Calculate the percentage of gravel as shown below.
Hence, the percentage of gravel is
Calculate the percentage of sand as shown below.
Hence, the percentage of sand is
Calculate the percentage of fines as shown below.
Hence, the percentage of fines is
Refer to Figure 1.
For soil B.
The percent passing through
The percent passing through
Calculate the percentage of gravel as shown below.
Hence, the percentage of gravel is
Calculate the percentage of sand as shown below.
Hence, the percentage of sand is
Calculate the percentage of fines as shown below.
Hence, the percentage of fines is
Refer to Figure 1.
For soil C.
The percent passing through
The percent passing through
Calculate the percentage of gravel as shown below.
Hence, the percentage of gravel is
Calculate the percentage of sand as shown below.
Hence, the percentage of sand is
Calculate the percentage of fines as shown below.
Hence, the percentage of fines is
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