Tensas gazette. [volume] (St. Joseph, La.) 1886-current, 1917-08-24
GOOD EARTH ROADS.
Much Depends on Soil, Construc-
ton and Maintenance.
LEADING QUALITIES OF SOILS
From Standpoint Of Road Building
They Depend on Texture and
Structure, PermeabIIity 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 Cd on
the quality of the soil composing the
roadbed. ca on proper construction
and (3) 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, its
stability may be increased greatly. In
general, a clay road, to be passable,
must be kept dry. and since clay Is very
difficult to drain, it happens seldom
that roads composed entirely of clay
can be kept in good condition at all
seasons of the year. No matter how
we'll such a 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 it 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
considerable time, even If thorough
ly saturated and sOftened, while COM
pressed balls from other varieties win
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 stabilizing effect by making the
clay more easily drained and increasing
Its bearing power when wet. In fact,
good quality Of clay mixed with
coarse sand in such proportions that
the clay fills the voids in the sand and
cements the individual particles to-
gether produces a soil which possesses
the good qualities Of both materials
and which overcomes, to a great extent,
the objections to each.
Sand.
SAM as composed "a granular par
ucles of mineral or stone v.hich occur
In nature and which will pass a one
fOurth-inch-mesh screen. The one
fourth-inch-mesh screen is fixed arbi-
trarily as the dividing line between
sand and gravel and is generally,
though not universally, accepted as
such. Nearly all sand consists essen
TALLY of quartz grains that are very
hard and durable. But there Is no Co
herence between the different grains
and therefore soils composed princi.
pally Of sand are unstable, except when
confined in some way. II properly con-
fined and protected from undermining
sand foundations may, under favorable
climatic conditions. prove entirely sat.
isfactory for almost any type of road
crust, but IL is practically impossible
| under any circumstances to make sat.
isfactory road surface of sand alone
Dry sand offers almost as great resist
ance to traffic as mud, and except in
very wet seasons sandy roads are likely
to dry out to a considerable depth. The
reason for this is that the capillary
power of sand is comparatively low
and the ground water elevation NAV be
lowered practically to the prevailing
level Of surface streams in extended
dry seasons.
Sand roads are at their best when
| they are kept moist, and for this rea
son they should be designed with q
view to retaining moisture In the sand
rather than to effective drainage, as Is
the case with clay roads. Such roads
sometimes are improved temporarily by
mixing sawdust, straw. pine leaves OF
other similar material into the surface
but, In general, the sand-clay crust 1.
the most satisfactory improvement fol
roads Of this character. This is true
especially where clay may be obtained
readily and only limited funds are
available for the improvement.