Page 90 - Buried Pipe Design

66 Chapter Three

The USCS is based on the textural characteristics for those soils
with a small amount of fines such that the fines have little or no influ-
ence on behavior. For those soils where fines affect the behavior, clas-
sification is based on plasticity-compressibility characteristics. The
plasticity-compressibility characteristics are evaluated by plotting the
plasticity chart. The position of the plotted points yields classification
information. The following properties form the basis of soil classifica-
tion and identification:
1. Percentages of gravel, sand, and fines [fraction passing 0.75-mm
(no. 200) sieve]
2. Shape of grain-size distribution curve (see Fig. 3.1)
3. Plasticity and compressibility characteristics (see Fig. 3.2)

Sieve Analysis

Percent Passing Percent Retained

Partical Size in Millimeters
Figure 3.1 Grain-size distribution curve for a particular soil. (Reprinted, by permission,
from ASTM D 2487, Fig. 4.)