The Union times. [volume] (Union, S.C.) 1894-1918, 1900-07-27
ROAD DISRUPTERS.
FORCES WHICH OPERATE TO DE-
STROT HIGHWAYS.

Frost Action a Potent Fnctor In tho
DiSinscErntion OF the FouEGatioE,.
Wear and Tear OF Natcr--Thc Linz
1T OK Grade.
1t has been the object of the highway
engineer ever since the days OF Mac
adam to construct roaA in such Il
manner that frost action above sub
grade may be reduced to Il minimum,
says &. l.. Whittle. Macadam contend.
cd strcnuousiy for dry foundation.
The evils resulting from the diSruptiug
effects of water alternately freezing
and thawiDg in the foundation of u
road arc too apparent and too well
known TO warrant rcS;atCment
There is no principle of greater impor
tancc than this, ana today engineers
differ only as to the best means ncccs-
sary to attain such all end. Frost ac-
ton is not only potent factor in dis
rupting Il road rs 4 whole, but its pres
cncc in stones is promotNc of weak
ness and more rapid crumblnS. The
presence Of frost in fragments Of bro
ken stone operates to increase their
brittlCnCSS to n considerable degree and
for this reason gives rise TO Il more
rapid diSiptcgration of the screenings
and the upper portion Of tho road. So
pcrnicious is this agent in causing brit
tlcnCsS that quarrymcn. where blasting
is necessary, SO time their work as to
avoid blasting operations during the
winter.
The ability of water as Il medium of
transportation of material by me-
chanical process depends upon the Spc-
ciiic gravity, the size and the form Of
the fragments and upon the velocity of
the water or, what amounts to the
same thing, the slope Of the roadbed.
The ratio of rise to horizontal distance
is largely 4 matter of custom, but )
per cent grade is now considered about
the limit of StCCpncss. 1t is not al
ways possible to obtain without great
expense Il grade of five feet in 100 in
some parts Of our country. but the
necessities OF sleeper grades are not
frequent in the eastern half of the
United States, although the old custom
in New England of building over rath,
cr than around the hills often makes
tic roads of this region excessively
steep.
The outlying OF roadbcdS during
heavy rains or melting SHOWS is the
most conspicuous work done by flow
ing water on our highways, yet we
should not pass by the sorting process
1t exercises even on gentle slopes,
where the grains of the least weight
ana specific gravity and of Tie most
tabular form are made to occupy the
surface of the road, thus, after drying,
falling an easy prey to the power OF the
wind. This sorting action arises from
the fact that, other things being equal,
the sand grains will arrange them
selves in water in the order of their
specific gravitics, the heaviest at the
bottom. An exception to this rule is
found when minerals even of high
specific gravity are charactcriSticall
Of tabular form, since the resistance
they offer to descent owing to their
relatively large surfaces, causes them
to arrange themselves at the top with
minerals Of tie lowest density.
The SLOW working water during Or
dinary rains;orms as it flows toward
the CUTTERS carries in its grasp the finer
grains Of quartz ana fcldSpar resulting
from the wear and tear Of Il roadway
of granite Eacadam. The mica usual
Is present il GRANTEES is very easily
transported both hy wind and water
action. owing; 10 its tabular character,
AMI tbs E:iHCval under all circum-
stances IS undesirable in road metals.
WlVa TIE necessities Of the case force
thr I:%r Cf granite rocks. it Is we'll to
select these. such as sycnitcs or gran
ties. continuing rs small q percentage