Table 2-1. A Simplified Classification of Natural Soil Deposits-Continued

f.

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

(2-1)

organic matter. The plasticity index (PI) is defined as

emax - emin

the difference between the LL and PL.

The liquidity

where

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

Alternatively,

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

yd

parameter for correlating engineering properties of soil.

d. Natural water content. The natural water

where

yd = dry unit weight of soil in its natural

content of a soil is defined as the weight of water in the

state

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

state

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

state

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

cubic foot.

Various weight-volume relationships are

soils.

presented in figure 2-3.

Integrated Publishing, Inc. |