Page 251 - Civil Engineering Formulas

CHAPTER 8
SOIL AND

EARTHWORK

FORMULAS

PHYSICAL PROPERTIES OF SOILS

Basic soil properties and parameters can be subdivided into physical, index, and
engineering categories. Physical soil properties include density, particle size and
distribution, specific gravity, and water content.
The water content w of a soil sample represents the weight of free water
contained in the sample expressed as a percentage of its dry weight.
The degree of saturation S of the sample is the ratio, expressed as percent-
age, of the volume of free water contained in a sample to its total volume of
voids V .
v
Porosity n, which is a measure of the relative amount of voids, is the ratio of
void volume to the total volume V of soil:
V v
n (8.1)
V
The ratio of V to the volume occupied by the soil particles V defines the void
v s
ratio e. Given e, the degree of saturation may be computed from
S wG s (8.2)
e
where G represents the specific gravity of the soil particles. For most inorganic
s
soils, G is usually in the range of 2.67 0.05.
s
The dry unit weight of a soil specimen with any degree of saturation may
d
be calculated from
w G s S
d (8.3)
1 wG s
3
3
where is the unit weight of water and is usually taken as 62.4 lb/ft (1001 kg/m )
w
3
3
for freshwater and 64.0 lb/ft (1026.7 kg/m ) for seawater.
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