CIVIL ENGINEERING FORMULAS

CHAPTER 8

185

SOIL AND

EARTHWORK

FORMULAS

PHYSICAL PROPERTIES OF SOILS

Basic soil properties and parameters can be subdivided into physical, index, and
engineering categories. Physical soil propertiesinclude density, particle size and
distribution, specificgravity, and water content.
Thewater content wof a soil sample represents the weight of free water
contained in the sample expressed as a percentage of its dry weight.
Thedegree of saturation Sof the sample is the ratio, expressed as percent-
age, of the volume of free water contained in a sample to its total volume of
voidsVv.
Porosity n,which is a measure of the relative amount of voids, is the ratio of
void volume to the total volume Vof soil:

(8.1)

The ratio of Vvto the volume occupied by the soil particles Vsdefines the void
ratio e. Given e,the degree of saturation may be computed from

(8.2)

whereGsrepresents the specific gravity of the soil particles. For most inorganic
soils,Gsis usually in the range of 2.670.05.
The dry unit weight dof a soil specimen with any degree of saturation may
be calculated from

(8.3)

wherewis the unit weight of water and is usually taken as 62.4 lb/ft^3 (1001 kg/m^3 )
for freshwater and 64.0 lb/ft^3 (1026.7 kg/m^3 ) for seawater.

d

wGsS

1 wGs

S

wGs

e

n

Vv

V