Classification of Soils for Engineering Purposes - Soil Properties: Testing, Measurement, and Evaluation - page 157

coarse fraction that passed the No. 4 sieve is 72.3%. Because 72.3%
is greater than 50%, go to the block labeled “Sands” in Table 11-3.
The soil is evidently a sand. Because the sample contains 15.2%
passing the No. 200 sieve, which is greater than 12% fines, go to the
block labeled “Sands with Fines—More than 12% fines.” Refer next
to the plasticity chart (Figure 11-3). With a liquid limit of 30.0%
and plasticity index of 18.0% (recall that the plasticity index is the
difference between the liquid and plastic limits, or 30.0 - 12.0 ), the
sample is located above the A-line, and the fines are classified as
CL. Return to Table 11-3, and go to the block labeled “SC.” Thus,
this soil is classified SC, according to the Unified Soil Classification
System.

Example 11-3
Given:
A sample of soil was tested in the laboratory with the following
results:
1. Liquid limit NP (nonplastic)
2. Plastic limit NP (nonplastic)
3. Sieve analysis data:

U.S. Sieve Size Percentage Passing

1 in. 100

⁄ 4 in. 85

3

⁄ 2 in. 70

1

⁄ 8 in. 60

3

No. 4 48

No. 10 30

No. 40 16

No. 100 10

No. 200 2

Required:
Classify the soil by the Unified Soil Classification System.
Solution:
Because the percentage retained on the No. 200 sieve (100 - 2, or
98%) is more than 50%, go to the block labeled “Coarse Grained
Soils” in Table 11-3. The sample consists of 100 - 2, or 98%, coarse-
grained sizes, and 100 - 48, or 52%, was retained on the No. 4 sieve.
Thus the percentage of coarse fraction retained on the No. 4 sieve
is 52/98, or 53.1%. Because 53.1% is greater than 50%, go to the
block labeled “Gravels” in Table 11-3. The soil is evidently a gravel.
Because the sample contains 2% passing the No. 200 sieve, which
is less than 5% fines, go to the block labeled “Clean Gravels—Less
than 5% fines.” The next block indicates that examination of the