Crossville chronicle. [volume] (Crossville, Tenn.) 1894-current, 1917-10-03
GOOD EARTH ROADS
Much Depends on Soil, ConStruc-
ton and Maintenance.
LEADING QUALITIES OF SOILS
From Standpoint of Read Suildina
They Depend on Texture and
q Structure, Permeability and
Capillary Power.

prepared by the United States Depart
ment of Agriculture)
Roads constructed by grading the
natural soil to the required shape,
grade and alignment, without special
surfacing of any kind, usually are des-
ignated as earth, or dirt, roads. The
efficiency of such roads depends (1) on
the quality of the soil composing the
rOadbed, (2) on proper construction,
and 81 on adequate maintenance.
Soils.
The principal qualities of soils from
the standpoint of road construction de-
pend upon texture and structure, per-
meability and capillary power. Soils
usually are classified as clay, sand,
loan, gravel, mari or gumbo, according
to the material predominating in their
composition. Soils composed of two
different materials mixed In such pro-
portions that the character Of the mix
ture Is decidedly intermediate may be
designated conveniently by naming
both components, as sand-clay, sand
gumbo, gravelly clay, etc.
Clay.
Clay Is soil of very fine texture
which results from the complete de-
composition of rocks or minerals. Pure
clay is very retentive of moisture, and
usually becomes plastic and unstable
when wet, but when mixed with other
materials, such as sand or. gravel, it's
stability may be increased greatly. In
general, clay road, to be passable,
must be kept dry, and since clay is very
difficult to drain, 1t happens seldom
that roads composed entirely Of clay
can be kept in good condition at all
seasons of the year. No matter how
well such road may be graded and
crowned, the surface absorbs water In
wet seasons and subsequent traffic will
produce mud. But when the road is
shaped and drained properly 1t will dry
out quickly when the weather becomes
favorable and may soon be restored
to its original shape On the other
hand, clay roads, when very dry, usu-
ally produce considerable dust under
traffic, and for this reason may become
very insanitary in extended dry sea-
sons.
The extent to which clay roads are
subject to the objections mentioned
above usually varies according to the
so-called shaking" qualities of the clay.
Some varieties of clay, when COM
pressed into ball and placed in water,
will continue in the original shape for
a considerable time, even If thorough
ly saturated and softened, while COM
pressed balls from other varieties will
slake or break down almost immedi-
ately upon being placed in water. Clays
of the aforementioned variety are called
"nonslaking clays," and Of the latter,
shaking clays." 1t has been observed
that shaking clays produce more mud
in wet weather and more dust in dry
weather than those Of the nonslaking
variety. This characteristic Of clays is
further considered in the discussion Of
sand-clay roads appearing in another
part Of this bulletin, where methods
for testing clay are suggested.
Most clays, as they occur in nature,
contain more or less sand or gravel,
which, as pointed out above, usually
has a stabilizlng effect by making the
clay more easily drained and increasing
its bearing power when wet.
Sand.
Sand is composed Of granular par
ticles Of mineral or stone which occur
In nature and which will pass a one
fourth-inch-mesh screen. The one
fourth-inch-mesh screen is fixed arbi-