TM 5-818-1 / AFM 88-3, Chap. 7
Table 2-1. A Simplified Classification of Natural Soil Deposits-Continued
Specific gravity. The specific gravity of the
U. S. Army Corps of Engineers
solid constituents of a soil is the ratio of the unit weight of
scribed manner. The PL is the water content at which the
the solid constituents to the unit weight of water. For
soil will just begin to crumble when rolled into threads 1/8
routine analyses, the specific gravity of sands and clayey
inch in diameter. Fat clays that have a high content of
soils may be taken as 2. 65 and 2. 70, respectively.
g. Relative density.
colloidal particles have a high LL, while lean clays having
Relative density is
a low content of colloidal parti- cles have a
defined by the following equation:
correspondingly low LL. A decrease in LL and PL after
either oven- or air-drying usually indicates presence of
DR(%) = emax - e X 100
organic matter. The plasticity index (PI) is defined as
emax - emin
the difference between the LL and PL.
index (LI) is defined as the natural water content wn,
emax = void ratio of soil in its loosest state
minus the PL, divided by the PI; i. e. , LI = (wn - PL)/PI.
e = void ratio in its natural state
The LI is a measure of the consistency of the soils. Soft
emin = void ratio in its densest possible state
clays have an LI approaching 100 percent; whereas, stiff
clays have an LI approaching zero.
c. Activity. The activity, A, of a soil is defined
DR(%) = yd - ydmin X
ydmax X 100 (2-2)
as A = PI/(% < 0.002 mm). The activity is a useful
ydmax - ydmin
parameter for correlating engineering properties of soil.
d. Natural water content. The natural water
yd = dry unit weight of soil in its natural
content of a soil is defined as the weight of water in the
soil expressed as a percentage of dry weight of solid
ydmin = dry unit weight of soil in its loosest
matter present in the soil. The water content is based
on the loss of water at an arbitrary drying temperature of
ydmax = dry unit weight of soil in its densest
1050 to 1100C.
e. Density. The mass density of a soil material
Thus, DR = 100 for a very dense soil, and DR = 0 for a
is its weight per unit volume. The dry density of a soil is
very loose soil. Methods for determining emax or cor-
defined as the weight of solids contained in the unit
responding densities have been standardized. Relative
volume of the soil and is usually expressed in pounds per
density is significant only in the case of coarse-grained
Various weight-volume relationships are
presented in figure 2-3.