The twice-a-week Twin Falls times. (Twin Falls, Idaho) 1916-1918, 1917-09-04


rant a highly improved surface, the
maximum grade usually is fixed with
reference to this feature about as fol-
lows:
Per cent
Coastal plain and prairie regions....2 to 3
Average rolling country ..............4 to 8 |
Hilly or mountainous regions........6 to s |
The question of minimum grade is |
of importance only as regards the side
bitches. These should have adequate
fall to empty the water that collects
in them at a sufficiently rapid rate to
prevent damage to the road Ordinar-
fly it Is desirable to give the side |
bitches fall of about one foot per 100 |
feet of length, though a somewhat less
fall has proved satisfactory some
times.
Wherever changes in grade occur
the change should be made by means
of a vertical curve, and not by an
abrupt angle.
Slopes.
The slope at which earth will stand
when faced up in a cut or placed in an
embankment depends (1) on the char
acter of the earth and (2) on the eli
mate. In cuts, good quality of nom
shaking clay usually will stand on a
slope of about 45 degrees, or, as slope
is expressed usually, one horizontal to
one vertical, even where fairly deep
freezing occurs, and in some of the
Southern states such material has been
known to stand for many years on
slope of less than one-half to one. On
the other hand, clay that Stakes very
easily, may require a slope of three to
one, or even four to one, under the most
favorable condition of climate, but
this latter extreme is very unusual.
The usual slope for clay in cuts is one
to one in warm climates and one and
one-half to one in cold climates.
While in the case of entertainments
clay usually can be deposited on an
initial slope of about one to one, this
steep slope seldom can be maintained
unless the material is of an exceptional
quality and the climate very favorable.
Ordinarily clay embankments should
have a slope of about two to one in
cold climates and at least one and one
half to one in warm climates; and If
the clay be of questionable quality
these values should be increased. EN-
bankment slopes require more care In
construction than excavation slopes,
because any flattening of an embank-
ment slope by the action Of weather
after the road is completed Is very
likely to damage the road surface /;
while the sliding in of excavation
slopes usually does no further damage
than to Ohstruct the side bitches,
which can be reopened readily.
Sand of average quality usually re-
quires a slope of about two to one in
cuts and three to one in embankments,
regardless of climate. Moderately
coarse sand mixed with gravel will
stand on a sleeper slope than fine
sand, because the former is not moved
so readily by the action of storm wa
ter
Solid rock excavation usually can be
done on an average slope of about one
fourth to one, except where the rock
occurs in sloping strata separated by
slippery clay seams. In the latter case
the average slope may be as much as
One-half to one or three-fourths to one.
The faces of rock cuts usually are not
dressed down to even an approximate
ly smooth slope, as Is done in earth
cuts. In excavating solid rock only
such material is moved as is actually
necessary to obtain the desired width
at the bottom of the cut or as has been
loosened in blasting. The faces should,
of course, be cleared of all material
which is loose, or which might be
loosened subsequently by frost and
slide down upon the road. Stone en-
bankments usually will stand on q
slope of about one to one.
In order to prevent damage by wash
ing all earth slopes in either excava-
ton or embankment should be protect.
ed by a growth of grass as soon as
practicable after they are formed.
In many localities where the soil is
fertile and n good quality Of grass is
native no seeding of the slopes is nee
essary. In other cases the soil may not
possess sufficient fertility to grow
grass, even when the slopes are seed
ed. and in which event it may be very
desirable to cover the slopes with cut
sod. This latter process usually is
very expensive, and should be EN-
ployed only where It is known thai
thorough seeding and fertilizing would
fail to secure a covering of sod.
Another precaution frequently neces
sary in order to prevent the washing
away of excavation slopes is to inter
cept water from the natural grount
} surface which otherwise would flow
, down over the excavation slope. Thi:
is done by means of "berm" ditcl
, constructed well back from the top o
the slope. Figure illustrates a con
, dition which makes a 'berm" ditcl
desirable and also shows how such |
l.