The Columbian. [volume] (Bloomsburg, Pa.) 1866-1910, 1893-03-24
MAKING A TeLFoRp ROAD.
Important Points to TO Observed In Sub
pavement and Top Course.

Important Points to 10 Observed In Sub.
pavement and Top Course.
The system of Thomas Telford, whose
name has been used to designate the kind
Of road which he advocates, differs from
the Macadam system in many particu.
lars, tho most important Of which pre-.
scribes the use of a subpavemont of large
stones set in courses upon the earth
foundation. In the interstices between
the larger stones should be carefully and
thoroughly wedged and packed with
smaller stones, AZ it insures the solidity
of the subpavement and serves TO pre-.
vent the dropping or settling of the ma.
terials that are subsequently put on.
When finished, the subpavement should
present general uniformity of outline
with n rough surface caused by the I'M.
even edges of the pavement stones-a
roughness which serves to prevent the
shifting and sloping of the smaller stones
above and to insure the compact binding
together of the entire structure.
In the making Of telford road it l.,
important to remember that the stones
used in the subpavement need not be Sc.
lected with regard to their hardness, and
that stones may be used in this part of
the work which would DO wholly un.
suited to situations where they might be
exposed TO direct contact with heavy We
hicles. Another practical point to be
remembered in the laying OF the sub.
pavement is that the driving and wedg-
ing OF chips and smaller stones into the
interstices Of tho subpavement must not
be permitted near the face Of the unfin.
ished work, as this practice would result
in the looseniny and forcing apart of the
larger stones OF the subpavement.
After the completion Of the subpave-
ment at least two separate layers Of
broken stone are generally put on to form
tho upper and finishing course Of the
roadway. Tho intermediate course next
to the subpavement is made of broken
stones somewhat after the. manner Of
macadam material, although these nee.
not be, and in practical work generally
are not, Of the same uniform size and
quality as are required for the finishing
layer. The stones used in the intermedi-
ate course may vary in size from inch
to 3 inches in their largest diameter, and
this course should be at least 4 inches
thick, free from dirt, and laid in bed
Of uniform thickness to preserve the
regular contour of the roadway.
In putting down this course the heavy
roller should again be employed to COM
pact and consolidate the stones, so that
the repeated passing Of the roller over
its surface will produce no settling. hol-
lows or uneven places. Before complet-
ing the rolling quantity of clean, sharp
sand should be laid on the surface Of the
intermediate course, evenly and in suffi-
eient amount, and over this the roller
should be passed repeatedly, after hav-
ing first sprinkled the sand with sriffi-
cient quantity of water to prevent its
sticking to the surface of the roller.
The top or surface course is the finish
ing work in the building of terford
road, and in the making Of this cou &C
great care must be had both in selecting
the material to be used and in the method
of laying it down. All the stones of this
course should be of uniform size, AID all
stones should be rejected from this ma
terial which are too large to pass through
ring having an inner diameter Of two
inches If trap rock can be obtained for
this course, it can be used with the as
surance that better material is scarcely
obtainable, buy il trap rock cannot he
had there are several varieties of hard
granite and limestone which make ex.
cellent substitutes and which are fre
quently used with success.
The top or surface course should be
laid with q uniform depth of not les.
| than 3 inches, and after being compactly
rolled it should show a thickness of al
| least inches above the intermediate
| course. After the loose stones for the
top course have been evenly laid ovei
| the surface of the intermediate course
80 as to show the form Of the completed
| roadway, the roller should be run ovel
| the new surface just enough to render il
moderately compact, and for this pur
pose light roller will be sufficient
| Then O light coat Of clean, sharp sand
should be put on and sprinkled rs in the
| case of the intermediate course, after
| Whcn, Dy tne use Oh Spliut orooiis, tnt
sand may be worked in between the
stones of the surface, while the heavy
| roller is made to follow, pressing the
small stones firmly into compact mass
The rolling should proceed backward
and forward in line with the direction OF
the road, beginning at the side or guttel
| OF the roadway and working toward the
center. The process Of rolling and add
| ing moist sand should continue until
| each stone becomes 30 firmly bedded and
the finished surface so hard that more
sand cannot be pressed into the surface
| after which all loose material remaining
on top Of the road may be removed, SC
as to leave the surface smooth and com
| plete.-Century.