Lesson 2/Learning Event 6
Learning Event 6
IDENTIFY THE PHYSICAL PROPERTIES OF SOIL AND THEIR EFFECTS ON
ENGINEERING
The physical properties which form the basis for the Unified Soil Classification System are the
percentages of gravel, sand, and fines; shape of the grain-size distribution curve; and plasticity. These
same properties are the primary ones to be considered in field identification, but other characteristics
observed should be included in describing the soil, whether the identification is made by field or
laboratory methods.
PHYSICAL PROPERTIES
The following is a list of the properties which the military engineer would include in a soil description:
Color
Grain size
-- estimated maximum grain size
-- estimated percent by weight of fines (material passing the #200 sieve)
Grain shape
Predominant soil type
Secondary components of soil
Classification symbol
Other remarks such as-organic, chemical, or metallic content
Compactness
Consistency
Cohesiveness near plastic limit
Dry strength
Source-residual or transported (aeolian, waterborne, glacial, deposit, etc.)
As stated before, these physical properties affect the engineering characteristics of the soil.
For
example, coarse-grained soils are better as a base in construction because they tend to drain better.
Table 5 illustrates the value of each soil type to construction based on its physical properties. The chart
is organized into coarse-grained and fine-gained soils. Each soil type is identified by both its common
name and its USCS symbol. By referring to this chart you will be able to describe any known soil's
engineering characteristics.
NOTE: The compressibility and expansion of a soil is usually an undesirable construction quality
(Table 5, Column 10). Thus, if a soil classified has a high to medium frost susceptible potential, then it
may disqualify that soil from being used in construction. Of course, it may be of little concern in a
project whether a soil expands, compresses, or has frost susceptibility. An
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