7.

USCS Symbol: SP-SM.

2

Fines equal 7 percent. The soil is coarse-grained and, since

sand is the predominant fraction, S is the primary letter. With 7

percent fines we know that we will have a dual classification and

that we have to consider both gradation and type of fines. The soil

does not meet the gradation criteria for sand, Cu = 3.8, which is not

greater than 6. Therefore, the second letter will be a P. By plotting

the LL and PI on the plasticity chart, we see that the fines are silty.

Therefore, the fourth letter is M. With the first and third letters of our

classification being the primary letter S, the whole symbol is SP-SM.

8.

USCS Symbol: OL.

2

The LL is below 50 percent so the secondary letter is L. The LL

and PI plot below the A-line on the plasticity chart indicating either a

silt or organic material. The description of the soil gives you the clue

that the material is organic, O. The primary letter is O and the

complete symbol is OL.

9.

c.

grain size distribution.

3

10.

c.

organic.

3

11.

d.

all of the above.

4 and 5

12.

d.

clay.

4

13.

a.

plasticity.

4

14.

ML is not suitable for airstrip construction because it has very

2, 4, and

high frost potential and fair to poor drainage.

6

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